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  • 1. Alexandrova, L
    et al.
    Hanumantha Rao, K
    Forsberg, KSE
    Grigorov, L
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Three-phase contact parameters measurements for silica-mixed cationic-anionic surfactant systems2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 348, no 1-3, p. 228-233Article in journal (Refereed)
    Abstract [en]

    The stability and interactions in thin wetting films between the silica surface and air bubble containing (a) straight chain C10 amine and (b) cationic/anionic surfactant mixture of a straight chain C10 amine with sodium C8, C10 and (straight chain) C12 sulfonates, were studied using the microscopic thin wetting film method developed by Platikanov [D. Platikanov, J. Phys. Chem. 68 (1964) 3619]. Film lifetimes, three-phase contact (TPC) expansion rate, receding contact angles and surface tension were measured. The presence of the mixed cationic/anionic surfactants was found to lessen contact angles and suppresses the thin aqueous film rupture, thus inducing longer film lifetime, as compared to the pure amine system. In the case of mixed surfactants heterocoagulation could arise through the formation of positively charged interfacial complexes. Mixed solution of cationic and anionic surfactants shows synergistic lowering in surface tension. The formation of the interfacial complex at the air/solution interface was confirmed by surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants system controls the strength of the interfacial complex. The observed phenomena were discussed in terms of the electrostatic heterocoagulation theory, where the interactions can be attractive or repulsive depending on the different surface activity and charge of the respective surfactants at the two interfaces.

  • 2. Alexandrova, L
    et al.
    Hanumantha, Rao K
    Forsberg, KSE
    Grigorov, L
    Pugh, Robert J
    YKI – Ytkemiska institutet.
    The influence of mixed cationic-anionic surfactants on the three-phase contact parameters in silica-solution systems2011In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 373, p. 145-151Article in journal (Refereed)
    Abstract [en]

    The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C14TAB) and (b) surfactant mixture of the cationic C14TAB with the anionic sodium alkyl- (straight chain C12-, C14- and C16-) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C14TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.

  • 3.
    Andersson, I. M.
    et al.
    Lund University, Sweden.
    Millqvist-Fureby, Anna
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Sommertune, Jens
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Alexander, M.
    Arla Foods Ingredients Group P/S, Denmark.
    Hellström, N.
    Lund University, Sweden.
    Glantz, Maria
    Lund University, Sweden.
    Paulsson, M.
    Lund University, Sweden.
    Bergenståhl, Björn
    Lund University, Sweden.
    Impact of protein surface coverage and layer thickness on rehydration characteristics of milk serum protein/lactose powder particles2019In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 561, p. 395-404Article in journal (Refereed)
    Abstract [en]

    Spray-dried powders were produced from milk serum protein concentrate and lactose in varying ratios, and the rehydration characteristics of the powders were evaluated. The dissolution rate was estimated with a flow-cell based technique, and the external and internal distribution of the powder components were evaluated with X-ray photoelectron spectroscopy and confocal Raman microscopy, respectively. The surface of the powder particles is more or less covered by a thin protein layer. A phase segregation between protein and lactose is observed in the interior of the particle resulting in a protein rich layer in the vicinity of the surface. However, the protein layer in the vicinity of the particle surface tends to become thinner as the bulk protein concentration increases in the powders (from 10 to 60% w/w). The time for the spontaneous imbibition to occur show a linear correlation with the protein surface coverage. The dissolution rate of powders containing 0.1% w/w protein is around 60 times faster than for a powder containing 1% w/w protein but the dissolution rate of powders containing 1% and 100% w/w differ only by a factor of 2. Thus, it is suggested that the outer protein layer becomes denser at the interface as the protein content increases in the powders, thereby causing poorer rehydration characteristics of the powders (especially for low protein concentrations 0.1–1% w/w). This insight has relevance for the formulation of whey protein powders with improved rehydration characteristics. © 2018 Elsevier B.V.

  • 4. Andersson, K
    et al.
    Kizling, J
    YKI – Ytkemiska institutet.
    Holmberg, K
    YKI – Ytkemiska institutet.
    Byström, S
    A ring-opening reaction performed in a microemulsion1998In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 144, p. 259-266Article in journal (Refereed)
  • 5. Arnold, Celine
    et al.
    Klein, Guillaume
    Maaloum, Mounir
    Ernstsson, Marie
    Larsson, Anders
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, YKI – Ytkemiska institutet.
    Marie, Pascal
    Surfactant distribution in waterborne acrylic films. 2 Surface Investigation2011In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 374, no 1-3, p. 58-68Article in journal (Refereed)
    Abstract [en]

    This paper presents results on sodium dodecyl sulfate (SDS) enrichment at the surface of pure acrylic or acrylic/laponite composite latex films. Surface concentrations were measured by Confocal Raman Spectroscopy leading to higher values than the nominal concentration of 6 wt%. X-ray Photoelectron Spectroscopy (XPS) analyses showed uppermost surface layers saturated with SDS in most cases. High resolution Atomic Force Microscopy (AFM) revealed a variety of morphologies for these surfactant top layers, highlighting the occurrence of SDS bilayers in different configurations. In an attempt to check for a correlation between the surface concentration of the surfactant in dry films and the concentration of free surfactant in water in the initial latex, this latter concentration was determined from the level of the plateau in adsorption isotherms. Adsorption studies by conductimetry showed an unexpected increase of the amount of adsorbed SDS with pH. The proposed interpretation is that, upon acrylic acid neutralization, the chains at the surface become more hydrophilic and spread out in water, revealing more sites for SDS to adsorb on. No correlation between free surfactant and surface enrichment could be established, indicating that the enrichment process is more complex than expected.

  • 6.
    Bergström, L
    YKI – Ytkemiska institutet.
    Shear thinning and shear thickening of concentrated ceramic suspensions1998In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 133, p. 151-155Article in journal (Refereed)
    Abstract [en]

    The steady shear properties of two important ceramic systems; Si3N4 powder and the composite system SiC whiskers and A1203 particles, has been investigated. The concentrated, colloidally stable powder suspensions displayed a shear thinning behaviour with an approach to a plateau at high shear rates. The concentrated aqueous SiCw and composite suspensions showed a strong, sometimes discontinuous, shear thickening at some critical shear rate which was attributed to a possible order-disorder transition of the suspension structure. It was possible to fit the volume fraction dependence of the colloidally stable ceramic suspensions to a modified Krieger-Dougherty model which yields values of the maximum volume fraction; Φm. Large differences in Φm could be correlated to the differences in shape between the whiskers and powders. The viscosity of the composite suspensions were sucessfully predicted from the Farris theory using the rheological data for the separate components.

  • 7.
    Blomberg, E
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Wärnheim, T
    Surface interactions in emulsion and liposome solutions1999In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 159, p. 149-157Article in journal (Refereed)
    Abstract [en]

    We have used two surface force techniques to investigate the interactions between hydrophilic and negatively charged mica and glass surfaces across concentrated and dilute oil-in-water emulsions, as well as across aqueous liposome solutions. It was observed with both the interferometric surface force apparatus, using mica surfaces, and with the non-interferometric MASIF technique, employing glass surfaces, that emulsion droplets adsorbed onto the surfaces. Under a high compressive force the adsorbed emulsion droplets were disintegrated and this resulted in a phase separation in the gap between the surfaces. The forces measured in the presence of the capillary condensate compared favourably with theoretical expectations. In contrast, no adsorption of large aggregates could be detected in the liposome solution. Instead it appears that upon adsorption the liposomes disintegrate and the surfaces become covered by a disordered layer of phospholipids. Measurements with the interferometric surface force apparatus, that allows absolute distances to be determined, allow us to draw the conclusion that some bilayer aggregates are adsorbed and that the inner layer consists of an intercalated monolayer.

  • 8. Blute, I
    et al.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    van de Pas, J
    Callaghan, I
    Industrial manufactured silica nanoparticle sols. 2: Surface tension, particle concentration, foam generation and stability2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 337, no 1-3, p. 127-135Article in journal (Refereed)
    Abstract [en]

    Several earlier papers have revealed that several key parameters, such as hydrophobicity (contact angle), size, shape and degree of agglomeration, have an important influence on the behavior of particles at the air/water interface. However, the origin of foaming with particles is still not clear. In this article, we have tentatively related surface tension measurements and particle concentrations to the generation and stability of foam produced fromindustrial manufactured silica nanoparticle sols. Surprisingly, only slight reductions in surface tensionwere observed and the differences between the hydrophophilic and partially modified hydrophobic sols were small. However, in the case of the partially modified hydrophobic sol, the surface tension/concentration gradient was found to be pH and concentration responsive. Also, the greatest reduction in surface tension was found to occur at low pH (in the region of the pHpzc) and could be related to the highest foamability (foam generation) as determined in our earlier publication [I. Blute, R.J. Pugh, J. van de Pas, I. Callaghan, Silica nanoparticle sols. 1. Surface chemical characterization and evaluation of the foam generation (foamability), J. Colloid Interface Sci. 313 (2007) 645–655]. Also, after centrifugation of the moderately hydrophobic modified concentrated sols, foaming tests carried out on the supernatant indicated that the particle concentration had a dominant influence on foamability and foam stability. Since only transient foams, with relatively short lifetimes, could be produced with thesemodified silica nanoparticles then (a) further surface modification or the reduction of pH to increase the surface activity or (b) the addition of a cosurfactant would be needed to increase the foamability and achieve foams with extended lifetimes.

  • 9. Blute, I
    et al.
    Svensson, M
    Holmberg, K
    YKI – Ytkemiska institutet.
    Bergh, M
    Karlberg, A-T
    Solution behavior of a surfactant aldehyde – the oxidation product of an alcohol ethoxylate1999In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 150, p. 105-113Article in journal (Refereed)
    Abstract [en]

    It has previously been shown that alcohol ethoxylates readily undergo autoxidation and that one of the major oxidation products is the surfactant aldehyde, i.e. an ethoxylate carrying a –CH2CHO group at the terminal end of the polyoxyethylene chain. In this work the cloud point, phase behavior and aggregation characteristics of the surfactant aldehyde produced by oxidation of C12H25(OCH2CH2)50H(CI2E5) are determined and compared with the values obtained with the parent surfactant. It was found that the physico-chemical behavior of the two species was very similar, which indicates that a considerable portion of the aldehyde group is in hydrated state, i.e. the surfactant aldehyde consists of a mixture of aldehyde in carbonyl form and the corresponding geminal diol. The cloud point of the surfactant aldehyde decreased rapidly with time, even when it was stored at low temperature. Also the parent surfactant and its homologue C12E6 exhibited a decrease in cloud point during storage. For instance, a 1% aqueous solution of C12E6 showed a cloud point decrease from 62 to 32°C after 4 months storage at 40°C. Such a change in solution behavior can have important practical implications.

  • 10. Blute, I
    et al.
    Svensson, M
    Holmberg, K
    YKI – Ytkemiska institutet.
    Bergh, M
    Karlberg, A-T
    Solution behaviour of a formate capped surfactant - the oxidation product of an alcohol ethoxylate.1999In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 160, p. 229-236Article in journal (Refereed)
    Abstract [en]

    The solution behaviour has been investigated for an alcohol ethoxylate terminated with a formic acid ester. This compound has previously been reported to be an important degradation product in the auto-oxidation of alcohol ethoxylates. In this work we have investigated the solution behaviour of the formic acid ester surfactant C12H25(OCH2CH2)4OCHO (C12E4-OCHO). The pure formate was found to be sparsely soluble in water with no clear point at 0.1%. The critical micelle concentration was found to be 129 µM at 35°C, compared to 50 µM for the parent surfactant C12H25(OCH2CH2)5OH (C12E5). To mimic the behaviour of the oxidised surfactant, the formate was mixed in different ratios with C12E5 and the cloud point, surface tension and critical micelle concentration of these mixtures were studied. The gradual increase of formate was found to shift the cloud point and isotropic regions to lower temperatures. The cmc of the mixture was found to be lower than for the pure surfactant. The favourable interaction was analysed according to the non-ideal model by Rubingh and the interaction parameter, b, was determined to be -4, which is unusually large for a mixture of two nonionic surfactants. These results indicate that the reduction of cloud point observed during oxidation of nonionic surfactants can in part be attributed to the formation of formate esters.

  • 11. Bodvik, Rasmus
    et al.
    Dédinaité, Andra
    YKI – Ytkemiska institutet.
    Karlson, Leif
    Bergström, Magnus
    Bäverbäck, Petra
    Skov Pedersen, Jan
    Aggregation and network formation of aqueous methylcellulose and hydroxypropylmethylcellulose solutions2010In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 354, no 1-3, p. 162-171Article in journal (Refereed)
    Abstract [en]

    Solution properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) have been investigated as a function of temperature and concentration using a broad range of experimental techniques. Novelties include the extensive comparison between MC and HPMC solutions as well as the combination of techniques, and the use of Cryo transmission electron microscopy (Cryo-TEM). The correlation between rheology and light scattering results clearly demonstrates the relation between viscosity change and aggregation. Cryo-TEM images show the network structures formed. Viscosity measurements show that for both MC and HPMC solutions sudden changes in viscosity occur as the temperature is increased. The onset temperature for these changes depends on polymer concentration and heating rate. For both MC and HPMC solutions the viscosity on cooling is very different compared to on heating, demonstrating the slow equilibration time. The viscosity changes in MC and HPMC solutions are dramatically different; for MC solutions the viscosity increases by several orders of magnitude when a critical temperature is reached, whereas forHPMCsolutions the viscosity decreases abruptly at a given temperature, followed by an increase upon further heating. Light and (SAXS) small-angle X-ray scattering shows that the increase in viscosity, for MC as well as for HPMC solutions, is due to extensive aggregation of the polymers. Light scattering also provides information on aggregation kinetics. The SAXS measurements allow us to correlate aggregation hysteresis to the viscosity hysteresis, as well as to extract some structural information. Cryo-TEM images give novel information that a fibrillar network is formed inMCsolutions, and the strong viscosity increase occurs when this network spans the whole solution volume. For HPMC solutions the behaviour is more complex. The decrease in viscosity can be related to the formation of compact objects, and the subsequent increase to formation of fibrillar structures, which are more linear and less entangled than for MC.

  • 12. Boschkova, K
    et al.
    Elvesjö, J
    Kronberg, B
    YKI – Ytkemiska institutet.
    Frictional properties of lyotropic liquid crystalline mesophases at surfaces2000In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 166, p. 67-77Article in journal (Refereed)
    Abstract [en]

    The lubricating effect of assemblies of amphiphiles at surfaces has been studied. Liquid crystalline mesophases were investigated in terms of frictional and wear properties in a pin on disc rig. It is shown that systems forming lamellar liquid crystals indeed serve as lubricating liquids, indicating that the lamellar liquid crystalline phase adsorb on the steel surface forming a lubricating tribofilm. Poor performance is obtained when the lubricating system is in a single phase, i.e. in this case a lamellar liquid crystalline region. However, good lubrication is found when the lamellar liquid crystalline phase is dispersed in the water. This is attributed to a low viscosity of the system rendering a fast relaxation of the system in order to form a new film after the disturbing action of the two sliding surfaces. The lamellar packing is altered by the addition of non-charged amphiphiles, such as short chain alcohols. Using different alcohols it was shown that aromatic short chain alcohols are detrimental to the wear. This was attributed to the Rebinder effect, i.e. a strong adsorption of the alcohol, which in turn facilitates crack formation and thus the wear. In systems with mixtures of cat- and anionic amphiphiles it was, not surprisingly found that the best lubrication is obtained with a slight excess of either surfactant.

  • 13.
    Claesson, P
    YKI – Ytkemiska institutet.
    Poly(ethylene oxide) surface coatings: Relations between intermolecular forces, layer structure and protein repellency1993In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 77, p. 109-118Article in journal (Refereed)
    Abstract [en]

    The adsorption of some ethylene oxide-containing surfactants and polymers has been studied using the surface force technique. The forces acting between surfaces coated with such surfactants and polymers have been investigated as a function of temperature. For all ethylene oxide-containing molecules studied, the general trends of the temperature dependence of the surface forces and the structure of the adsorbed layer can be rationalised by considering the temperature dependence of the interaction between the ethylene oxide group and water. The different polymers and surfactants differ however in terms of surface affinity and in terms of the range of the surface forces. Knowledge of the surface forces acting between poly(ethylene oxide) layers can be used to establish why such coatings show a low protein adsorption, particularly at low temperatures.

  • 14.
    Claesson, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Surface forces and friction between non-polar surfaces coated by temperature-responsive methylcellulose2014In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 441, no Jan, p. 701-708Article in journal (Refereed)
  • 15.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Measurements of surface interactions1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 123, p. 339-340Article in journal (Refereed)
  • 16.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Paulson, O
    Malmsten, M
    Adsorption and interaction of a graft copolymer of poly(ethylene imine) and poly(ethylene oxide)1996In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 112, p. 131-139Article in journal (Refereed)
    Abstract [en]

    The adsorption of proteins and particles onto surfaces carrying firmly adsorbed or covalently bound chains of poly(ethylene oxide) (PEO) is generally very low. This makes it of fundamental and practical interest to learn about the structure of PEO-coatings and how PEO-coated surfaces interact with each other and e.g. proteins. A prerequisite for such studies is, of course, that stable PEO-coated surfaces can be obtained. For this purpose we employed a two-step method to coat negatively charged surfaces, such as mica or silica, with PEO. In the first reaction step, cationic poly(ethylene irnine) is adsorbed onto the negatively charged surface. In the next step, the adsorbed polyelectrolyte is reacted with a functionalized poly(ethylene oxide) chain. Both reaction steps were followed both by ellipsometry and by direct measurement of surface forces. From these measurements we obtained inforrnation of the adsorbed amount, the layer thickness, as well as the range and distance dependence of the interaction between two PEO-coated surfaces.

  • 17.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Dahlgren, MAG
    YKI – Ytkemiska institutet.
    Eriksson, L
    Forces between polyelectrolyte-coated surfaces: relations between surface interaction and floc properties1994In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 93, p. 293-303Article in journal (Refereed)
    Abstract [en]

    The forces acting between negatively charged mica surfaces in the presence of some different cationic polyelectrolytes have been measured using a surface force apparatus. The different polyelectrolytes used have between 10% and 100% of the monomers charged. Particular emphasis has been given to the forces acting between the polyelectrolyte-coated surfaces when the ionic strength of the solution is low, i.e. when electrostatic forces predominate the interaction between the surface and the polyelectrolyte. Under these conditions the most highly charged polyelectrolytes adsorb in a very flat conformation and only a weak recharging is observed even at polyelectrolyte concentrations considerably above that needed to neutralise the mica surface charge. The surface force data are discussed in relation to the floc structures and properties obtained when latex particles are flocculated by polyelectrolytes. These studies are carried out by using a device that is based on three photometric dispersion analysers. The floc structures formed in the presence of various polyelectrolytes can to a large extent be rationalised by considering the interactions measured in the surface force apparatus provided that the difference in charge density of the mica surface and the latex surface is kept in mind.

  • 18.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Paulson, OEH
    Blomberg, E
    YKI – Ytkemiska institutet.
    Burns, NL
    Surface properties of poly(ethylene imine)-coated mica surfaces - salt and pH effects1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 123, p. 341-353Article in journal (Refereed)
    Abstract [en]

    The adsorption of a branched weak polybase, poly(ethylene imine) (PEI), on the basal plane of muscovite mica was investigated using surface force measurements, electro-osmotic measurements, and ESCA. The use of this combination of techniques allows us to obtain information about adsorbed amount, interfacial charges, average structure of adsorbed layers and the most important types of forces acting between PEI-coated surfaces. The system was studied under two different conditions. The adsorbed layer adopts a flat conformation at low ionic strength ant at low pH owing to the predominance of electrostatic forces. The interfacial properties of PEI-coated surfaces are compared with those of strong polyelectrolytes as well as with a linear weak polybase studied previously under similiar conditions. At higher pH-values the adsorbed amount increases owing to a reduction in the polyelectrolyte charge density. This results in a thicker layer and in the increased importance of repulsive steric forces. Finally, the interaction between one polyelectrolyte-coated surface and a bare mica surface was investigated and compared with recent theoretical predictions.

  • 19. Djuve, J
    et al.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Sjöblom, J
    Foaming and dynamic surface tension of aqueous polymer/surfactants solutions 1: ethyl(hydroxyethyl) cellulose and sodium dodecyl sulphate2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 186, p. 189-202Article in journal (Refereed)
    Abstract [en]

    Foaming (in a column) and dynamic surface tension behaviour of aqueous solutions of sodium dodecyl sulphate (SDS), and ethyl (hydroxy ethyl) cellulose/ sodium dodecyl sulphate (EHEC/SDS) mixtures was determined. The results indicated a synergism in foaming and surface activity for the EHEC/SDS mixtures over a specific concentration range. For the SDS solution, the maximum value in Marangoni Elasticity (EM max), as determined from dynamic surface tension data, was reached within a surface age of 0.05s and it could be suggested that in this case EM max was relevant to foam stability. However, for the EHEC (non-foaming solutions), EM max was reached after longer surface ageing periods (0.05-0.1 s). For the EHEC/SDS solutions, EM max occurred over a range of surface ageing periods depending on the polymer/surfactant ratio and no correlation was obtained between EM max and foaming. The EM max time lag for the polymer and polymer/surfactant mixtures was explained by the slower diffusion from solution to the new surface. For the EHEC/SDS, the enhanced the foaming behaviour was explained by the adsorption of surface active polymer/surfactant (clusters) species at the air/solution interface. It was suggested that this could lead to coherent (gelatinous) interfacial layers in the thin film lamella which reduce drainage from the central fluid.

  • 20.
    Eriksson, JC
    et al.
    YKI – Ytkemiska institutet.
    Ljunggren, S
    Kegel, WK
    Lekkerkerker, HNW
    Entropy and droplet size distributions of Winsor I and II microemulsions2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 183-185, p. 347-360Article in journal (Refereed)
    Abstract [en]

    A review is presented of some general notions underlying the current theory of Winsor I and II microemulsions where the exposition is based on a comparison between the droplet kind of approach with the corresponding multiple equilibrium treatment. We show that the droplet size distributions derived earlier, although put in different mathematical forms in the respective treatments, are in effect the same, of the type where the preexponential factor, S(R), is due to the fluctuations in size and shape of the droplets, and the droplet surface tension, s, is curvature-dependent in accordance with the Helfrich expression. Full consistency is demonstrated among the two approaches, at least insofar as surfactant density fluctuations are not explicity taken into account. Moreover, on the basis of the multiple equilibrium model we can actually estimate the length scale parameter l introduced earlier in the droplet kind of treatment to fully account for the entropy of dispersion, to be about 1 nm, in fair agreement with previous estimates

  • 21.
    Eriksson, L
    et al.
    YKI – Ytkemiska institutet.
    Alm, B
    YKI – Ytkemiska institutet.
    Stenius, P
    YKI – Ytkemiska institutet.
    Formation and structure of polystyrene latex aggregates obtained by flocculation with cationic polyelectrolytes. I. Adsorption and optimum flocculation concentrations1993In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 70, p. 47-60Article in journal (Refereed)
    Abstract [en]

    The adsorption of modified polyacrylamide polyelectrolytes and their effect on the flocculation of negatively charged polystyrene latex was investigated. Conditions were chosen so that the adsorbed polymers approached equilibrium configuration before the occurrence of appreciable flocculation. Polymers with very low charge density ( a few % charged monomers) form loops and tails at the latex surface and flocculate the latex by bridging. Polymers with higher charge adsorb in a flat configuration and flocculate the latex by net charge neutralization, possibly leading to long-range attraction between positively and negatively charged domains on different particles. Minima in the ratio of the total polymer charge adsorbed at the plateau level to the total charge on the latex occur at intermediate polymer charge densities. At these densities the mean distance between charge groups on the polymers matches the mean distance between charged groups on the latex. At maximum adsorption of highly charged polymers the latex particles acquire a high positive charge. The reason for this is that the mean distance between positive charges on the polymer is smaller than the distance between charges on the latex, so that ion binding of the polymer to the ionized latex surface groups cannot take place without simultaneous attachment of an excess of positive charge to the latex surface.

  • 22.
    Ernstsson, M
    et al.
    YKI – Ytkemiska institutet.
    Larsson, A
    YKI – Ytkemiska institutet.
    A multianalytical approach to characterize acidic adsorption sites on a quartz powder2000In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 168, p. 215-230Article in journal (Refereed)
    Abstract [en]

    In this paper three methods are described to estimate the number of adsorption sites and detect adsorption sites of differing nature on mineral surfaces. The methods are solution depletion adsorption isotherms, adsorption microcalorimetry, and desorption by solvent extraction followed by surface analysis using Electron Spectroscopy for Chemical Analysis (ESCA). The number of adsorption sites is obtained from the adsorbed amount of a test molecule on a mineral surface from the ESCA data using equations based on a substrate/overlayer model, and from the adsorption isotherms the number of sites available to accommodate a monolayer of test molecules is used. Information about whether the adsorption sites are of different or similar nature is provided by the desorption method using extraction in solvents of different polarities. More quantitative information concerning interactions between test molecules and adsorption sites, and possible interaction strength distribution due to sites of differing nature, is obtained from the adsorption enthalpies measured by microcalorimetry. The systems studied included strong basic test molecules (either a fatty diamine, octadecyl amine or pyridine) adsorbed on quartz powder from a nonpolar medium, n-octane. For the desorption study, subsequent extraction was carried out in pure n-octane, followed by ethanol. Adsorption/desorption of basic test molecules on quartz is important in applications of asphalt systems where fatty amines are often added to strengthen adhesion between bitumen and stone aggregates. The quartz powder studied here has acidic adsorption sites of differing nature on the surface. The strong interaction sites are consistent with iron oxide and/or oxohydroxide (strongest interactions with the fatty diamine where both nitrogen atoms can interact) and geminal hydroxyl groups. The weaker interaction sites are consistent with hydroxyl (silanol) groups forming hydrogen bonds with the basic test molecules.

  • 23.
    Folmer, BM
    et al.
    YKI – Ytkemiska institutet.
    Holmberg, K
    YKI – Ytkemiska institutet.
    The cross sectional headgroup area of nonionic surfactants; The influence of polydispersity2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 180, p. 187-191Article in journal (Refereed)
    Abstract [en]

    In this work we have measured surface tension as a function of concentration of pure and technical nonionic ethoxylated surfactants. CMC values, surface tension at the CMC and the cross sectional headgroup areas are compared. It is shown that the CMC does not depend significantly on the polydispersity of the polyoxyethylene chain. However, the surfactant headgroup area, as determined from the surface tension plots, are much smaller for polydisperse surfactants than for homologue pure surfactants. This is due to the selective adsorption of the shorter polyoxyethylene species at the surface. For the same reason the surface tension at the CMC is lower for technical surfactants than for homologue pure species.

  • 24. Fäldt, P
    et al.
    Bergenståhl, B
    YKI – Ytkemiska institutet.
    The surface composition of spray-dried protein-lactose powders1994In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 90, p. 183-190Article in journal (Refereed)
    Abstract [en]

    The surface composition of spray-dried mixtures of lactose/protein and lactose/glycine were estimated by means of ESCA. The results show that even with a low concentration of protein (0.01% wt) in the solution to be dried, protein starts to appear on the surface of the powder. At a protein/lactose ratio of 1/99 the protein starts to dominate the powder surface. At a protein/lactose ratio of 20/80, ~70 % of the surface is covered by protein. The results are similar for the proteins sodium caseinate and bovine albumin. The spray-drying of mixtures of lactose/glycine gives a different result. In this case, the surface composition of the powder reflects the composition of the mixture to be dried The surface tensions of the solutions show that the proteins have a higher surface activity than lactose, since even a small amount of protein added to a lactose solution lowers the surface tension considerably. Glycine affects the surface tension to only a minor extent. These results show that the composition of the air-water interface of the drying droplets is reflected in the surface composition of the dried powder. In addition, scanning electron microscopic pictures show that the changes in the powder structure when protein is added to the solution are associated with the presence of protein on the surface. When the surface coverage of protein increases, dents start to appear on the particles. The powders made from lactose/glycine solutions are highly agglomerated regardless of the glycine concentration.

  • 25. Gutfelt, S
    et al.
    Kizling, J
    YKI – Ytkemiska institutet.
    Holmberg, K
    YKI – Ytkemiska institutet.
    Microemulsions as reaction medium for surfactant synthesis1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 128, p. 265-271Article in journal (Refereed)
    Abstract [en]

    Various microemulsion formulations were evaluated as reaction medium for synthesis of a surface active compound, decyl sulfonate, from decyl bromide and sodium sulfite. The reaction rate was fast both in water-in-oil and in bicontinuous microemulsions based on nonionic surfactant. Two-phase systems with added phase transfer agent (quaternary ammonium salt or crown ether) was much less efficient. It is postulated that the low efficiency of the phase transfer agents in catalyzing the reaction is caused by strong ion pair formation between the product formed, decyl sulfonate, and the phase transfer agent. To prove this point decyl bromide was reacted with two other nucleophiles, sodium cyanide and sodium azide. Neither of these give a reaction product that can form ion pair with the phase transfer agent. With these reagents phase transfer catalysis was almost as efficient as synthesis in microemulsion. It was also demonstrated that the rate of decyl sulfonate formation in microemulsion can be increased further by addition of a small amount of cationic surfactant. The choice of surfactant counterion is decisive of the effect on reaction rate, however. Whereas a small non-polarizable ion, such as acetate, gives a considerable reaction rate increase, a large polarizable ion, such as bromide, slows down the reaction. Bromide is believed to interact so strongly with the interface that it prevents the reacting ion, sodium sulfite to reach into the interfacial zone.

  • 26.
    Hamngren Blomqvist, Charlotte
    et al.
    Chalmers University of Technology, Sweden.
    Abrahamsson, Christoffer
    Chalmers University of Technology, Sweden.
    Gebäck, Tobias
    Chalmers University of Technology, Sweden.
    Altskär, Annika
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Food and Bioscience, Structure Design. Chalmers University of Technology, Sweden.
    Hermansson, Anne-Marie
    Chalmers University of Technology, Sweden.
    Nyden, Magnus
    Chalmers University of Technology, Sweden; University of South Australia, Australia.
    Gustafsson, Stefan
    Chalmers University of Technology, Sweden.
    Loren, Niklas
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Food and Bioscience, Structure Design. Chalmers University of Technology, Sweden.
    Olsson, Eva
    Chalmers University of Technology, Sweden.
    Pore size effects on convective flow and diffusion through nanoporous silica gels2015In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 484, p. 288-296Article in journal (Refereed)
    Abstract [en]

    Material structure has great impact on mass transport properties, a relationship that needs to be understood on several length scales. Describing and controlling the properties of flow through soft materials are both challenges concerning the industrial use of gel structures. This paper reports on how the porous structure in nanoporous materials affects the water transport through them. We used three different silica gels with large differences in the pore sizes but of equal silica concentration. Particle morphology and gel structure were studied using high-resolution transmission electron microscopy and image analysis to estimate the pore size distribution and intrinsic surface area of each gel. The mass transport was studied using a flow measurement setup and nuclear magnetic resonance diffusometry. The average pore size ranged from approximately 500 nm down to approximately 40 nm. An acknowledged limit for convective flow to occur is in the pore size range between 100 and 200 nm. The results verified the existence of a non-linear relationship between pore size and liquid flow at length scales below 500 nm, experimentally. A factor of 4.3 in flow speed separated the coarser gel from the other two, which presented almost identical flow speed data despite a factor 3 in pore size difference. In the setup, the mass transport in the gel with the largest pores was flow dominated, while the mass transport in the finer gels was diffusion dominated. Besides providing new insights into mass transport as a function of pore sizes, we conclude that three-dimensional analysis of the structures is needed for a comprehensive understanding of the correlation between structure and mass transport properties.

  • 27. Hellebust, S
    et al.
    Blokhus, AM
    Nilsson, S
    YKI – Ytkemiska institutet.
    Associative and segregative phase behaviour of a mixed aqueous cationic surfactant and anionic hydrophilic polymer system2004In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 243, p. 133-138Article in journal (Refereed)
    Abstract [en]

    The phase behaviour of a mixture of a highly charged hydrophilic polymer, dextran sulphate sodium salt, and a cationic surfactant, tetradecyltrimethylammonium bromide, was investigated in aqueous solution of different ionic strengths. The system has the interesting and novel property that at certain ionic strengths it displays both segregative and associative phase behaviour separated by a single-phase region within the same phase diagram. By increasing the ionic strength further the segregative area increases and the associative area disappears. In addition, the effect of cosolutes n-octane and 1-octanol on the above-mentioned phase behaviour has been studied. The effect of the former was to increase the miscibility and the latter to decrease the miscibility.

  • 28.
    Hermansson, M
    YKI – Ytkemiska institutet.
    The fluidity of hydrocarbon regions in organo-gels, studied by NMR. Basic translational and rotational diffusion measurements1999In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 154, p. 303-309Article in journal (Refereed)
    Abstract [en]

    Organogels composed of 12-hydroxystearic acid (12-HSA) and low-viscosity solvents such as decane, decalin and ethyl acetate have been used as model systems for lubricating greases. The fluidity of perdeuterated probe molecules in the above mentioned model systems was studied using two NMR spectroscopy methods. First translational diffusion was studied for the perdeuterated probes benzene, toluene, decane and dodecane by pulsed-field gradient NMR. The probes were introduced into a commercial lubricating grease and the model systems mentioned above. Secondly, the rotational diffusion tensor for perdeuterated trans-decalin was studied by deuterium spin relaxation measurements. All probed samples contained 5% probe (by total mass). The measurements show that the microviscosity in the gels is quite similar to the bulk viscosity in the corresponding neat solvent. This indicates that no strong interactions occur between 12-HSA and it also indicates that the obstruction effect is responsible for the decrease in the diffusion rate compared to the neat solvents in 12-HSA-thickened systems.

  • 29.
    Holmberg, K
    et al.
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Brink, C
    Grafting with hydrophilic polymer chains to prepare protein-resistant surfaces1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 123-124, p. 297-306Article in journal (Refereed)
    Abstract [en]

    Different ways of grafting poly(ethylene glycol) (PEG) chains to solid polyethylene were compared with respect to grafting density and efficiency in preventing fibrinogen adsorption. Covalent grafting of PEG was performed by attaching a nucleophilic PEG derivative to electrophilic surface groups or by binding electrophilic PEG to nucleophilic groups at the solid surface. Two adsorption procedures were also used. In the first of these an ethylene oxide - propylene oxide (EO-PO) block copolymer was adsorbed at unmodified, hydrophobic polyethylene. In the second procedure the surface was made carboxyl-functional by free radical grafting of tiglic acid and then exposed to a solution of a positively charged copolymer consisting of PEG chains grafted to poly(ethylene imine) (PEI). According to ESCA measurements, all four routes gave proper PEG grafting densities and the difference in the ratio of C–C–O carbon (from PEG) to C-C-C  carbon (from the underlying surface) was relatively small. There was a substantial difference in efficiency in fibrinogen rejection, however. Whereas surface modification with the PEG-PEI graft copolymer gave the lowest, treatment with the EO-PO block copolymer gave the highest amount of protein adsorption. The good effect of the PEG-PEI layer is believed to be related to the large entropy loss associated with protein adsorption on top of this copolymer which is known to be loosely bound in a loops-and-trains configuration. The limited effect of the EO-PO block copolymer may be due to the fact that this polymer is not entirely hydrophilic at the temperature used. Another contributing factor may be that the EO-PO block copolymer, unlike the PEG-PEI graft copolymer, is not irreversibly bound to the surface and may therefore be exchanged by fibrinogen.

  • 30. Holmberg, M
    et al.
    Wigren, R
    Erlandsson, R
    Claesson, PM
    YKI – Ytkemiska institutet.
    Interactions between cellulose and colloidal silica in the presence of polyelectrolytes1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 129-130, p. 175-183Article in journal (Refereed)
    Abstract [en]

    The forces acting between two cellulose surfaces and a cellulose surface and silica have been investigated using the interferometric surface force technique and the scanning force microscopy colloidal-probe technique. A key element in this study is the preparation of very smooth cellulose surfaces using a Langmuir Blodgett technique, which facilitates a detailed characterisation of the forces acting between the surfaces as a function of their separation. The main part of the investigation is concerned with the effect of a highly charged cationic polyelectrolyte, PCMA, on the interaction between negatively charged silica and uncharged cellulose. It is found that the presence of the cationic polyelectrolyte reduces the force barrier against flocculation, but also the attractive pull-off force. The implications of these findings for the function of this polyelectrolyte as a retention aid and a wet strength additive is discussed. The ionic strength of the solution has profound effects on the interactions between cellulose and silica in the presence of PCMA. This is due to a decreased polyelectrolyte-surface affinity at higher ionic strengths.

  • 31.
    Huldén, M
    YKI – Ytkemiska institutet.
    Hydrophobically modified urethane-ethoxylate (HEUR) associative thickeners. 1. Rheology of aqueous solutions and interactions with surfactants1994In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 82, p. 263-277Article in journal (Refereed)
    Abstract [en]

    The rheological properties of aqueous solutions of hydrophobically modified ethylene oxide urethane block copolymers, or HEUR thickeners, of different chemical compositions have been studied. A steep increase in viscosity with increasing thickener concentration is obtained at a concentration that increases with decreasing polymer molecular weight as predicted by a simple network model. However, this model does not predict the efficiency of the thickener, that is greatly effected by the hydrophobicity of the terminal hydrocarbon chains, and decreases in the order octadecyl > pentadecyl > 9-heptadecenyl. The more hydrophobic the end groups, the stronger are the crosslink points in the network, and as a consequence the more elastic is the solution. In HEUR solutions adjusted to the low shear viscosity 10 Pa s, 6-12 % of the thickener molecules are elastically effective in the network and the upper limit of the aggregation number is 40-60. The addition of surfactant increases the viscosity of the HEUR solutions, until, for most systems, a maximum is reached after which the viscosity decreases. The magnitude of the variation in viscosity is dependent on the chemical structures of both the polymer and the surfactant. The observed differences can be explained qualitatively by stoichiometric considerations of the mixed aggregates that are assumed to be formed between the hydrophobic chains of the polymer and the surfactant. Additional informa-tion relating to the HEUR-surfactant interaction was obtained from surface tension measurements. A nonionic surfactant is bound by a noncooperative process only to the hydrophobic aggregates of the HEUR. Sodium dodecyl sulphate is bound both to the hydrophobic domains and to the ethylene oxide blocks of the HEUR polymers.

  • 32.
    Huldén, M
    YKI – Ytkemiska institutet.
    Hydrophobically modified urethane-ethoxylate (HEUR) associative thickeners. 2. Interaction with latex1994In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 88, p. 207-221Article in journal (Refereed)
    Abstract [en]

    The rheological behaviour of model latexes thickened with hydrophobically modified ethylene oxide urethane block copolymers, i.e. HEUR type associative thickeners, is described. The latex particle size, as well as the type and level of surfactant used, greatly effect the thickening efficiency of the HEUR. Measurements of the electrophoretic mobility of the latex particles at different HEUR concentrations indicate adsorption of the thickener in the absence of surfactant and in the presence of nonylphenol ethoxylate, NPE1o. However, the HEUR thickeners do not adsorb to the latex particles in the presence of sodium dodecyl sulphate, SDS, at levels above the cmc of the surfactant. This can be explained by SDS-HEUR interactions in the solution. Both adsorption and rheological measurements support a latex-HEUR association mechanism, according to which the particles are incorporated through adsorption of their hydrophobic endgroups into a three dimensional transient thickener network. At a given volume fraction, latexes with a small particle size present a larger number of potential crosslink points at shorter distances from each other. This leads to a synergistic increase in viscosity on addition of HEUR to the latex. A HEUR-thickened latex that exhibits such a synergistic viscosity increase is more shear thinning and elastic than an aqueous HEUR solution of comparable low-shear-rate viscosity. This may be explained by the assumption that the latex particles introduce stronger crosslink points in the network in addition to the micelle-like hydrophobic aggregates which act as crosslink points in aqueous solutions of HEUR. Variations in the chemistry of the HEUR affect both the level of the low-shear-rate viscosity and the shear thinning behaviour of the thickened latex. Octadecylterminated HEUR's produce latex systems that are more shear thinning and elastic than HEUR's with shorter hydrophobic modifications (i.e. with pentadecyl or 9-heptadecenyl terminations). However, the latter are less efficient in increasing the viscosity at low an medium shear rates. The effect of the molecular weight of the HEUR is mainly to increase the length of the network junctions between the crosslink points. As a result the greatest thickener efficiency is obtained with medium molecular weights. The effects on the rheology of thickened latex obtained by varying the HEUR composition parallel the effects seen in aqueous solution. This does not mean that the solution properties dominate in the rheological behaviour, but rather that both types of crosslinks present in the HEUR-latex network are affected in similar ways by variations in the HEUR chemistry. This is reasonable, as both crosslinks are a product of hydrophobic interactions.

  • 33. Hunter, TN
    et al.
    Wanless, EJ
    Jameson, GJ
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Non-ionic surfactant interactions with hydrophobic nanoparticles: Impact on foam stability2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 347, no 1-3, p. 81-89Article in journal (Refereed)
    Abstract [en]

    The interactive behaviour of particles and surfactant at an air–water interface has been investigated, with particular reference to the effect of the interactions on the stability of air–water foams. For a system combining octyl grafted silica particles and Triton X-100, the effects of both individual particles and surfactants with the interface have been considered, along with particle–surfactant interactions. Because of the complexity of the system, the change in aqueous foam stability was inferred from a number of key parameters: namely, the bulk adsorption of surfactant onto the particles, the combined influence on system interfacial tension, the role of surfactant on particle aggregation and the role of interfacial elasticity. It was found that adsorption on the particles occurred in a two-stage process, with an initial Langmuir monolayer being augmented as interactions between surfactant aromatic moieties produced a perpendicular arrangement with head-groups facing into the solution, rendering the particles completely hydrophilic at high concentrations. At low-to-moderate concentrations of surfactant, the foam stability was increased by ∼20% in comparison to pure particle systems. The reasons for the improved stability were two-fold. Firstly, in low concentrations, surfactant caused bridging flocculation of the particles at the interface, producing enlarged sterically strong interfacial barriers. Secondly, at moderate concentrations, the surface elasticity was increased by the presence of the surfactant. The maximum interfacial elasticity was higher in composite systems, in comparison to pure surfactant solutions, probably a result of reduction in available interfacial area for adsorption of free surfactant to the air–water interface.

  • 34. Häger, M
    et al.
    Holmberg, K
    YKI – Ytkemiska institutet.
    d'A Rocha Gonsalves, AMA
    Serra, AC
    Oxidation of azo dyes in oil-in-water microemulsions catalyzed by metalloporphyrins in presence of lipophilic acids2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 183-185, p. 247-257Article in journal (Refereed)
    Abstract [en]

    Hydrogen peroxide oxidation of two aqueous azo dyes, methyl orange and amaranth, catalyzed by manganese porphyrins, have been performed in an oil-in-water microemulsion based on a nonionic surfactant, C12E8. A lipophilic acid was used as cocatalyst in a variable amount. The oxidation was followed by UV spectroscopy. It was shown that the reactions performed in the microemulsion were rapid for both dyes and the reaction rate increased strongly with increasing amount of lipophilic acid added to the reaction mixture. As reference, the same reactions were performed in a two-phase system without surfactant. The reaction profiles in the two-phase system were similar to those in the microemulsion, but the rate was considerably lower. The effect of addition of small amounts of ionic surfactant was also investigated. Addition of anionic surfactant gave a pronounced decrease in reaction rate, whereas a cationic surfactant gave a small reduction in rate. We propose that the rate-limiting step is formation of a metallo-acylperoxy complex at the boundary between oil and water domains. The metallo-acylperoxy complex oxidizes the azo dye in a subsequent step.

  • 35. Häger, M
    et al.
    Holmberg, K
    YKI – Ytkemiska institutet.
    Olsson, U
    Synthesis of an amphiphilic polymer performed in an oil-in-water microemulsion and in a liquid lamellar crystalline phase2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 189, p. 9-19Article in journal (Refereed)
    Abstract [en]

    A nucleophilic addition reaction between a hydrophilic hydrazide, the hydrazide of polyethylene glycol with a molecular weight of 3400, and a hydrophobic aldehyde, has been performed in a microemulsion and a lamellar liquid crystalline phase of a ternary non-ionic surfactant-water-oil system. As a reference the same reaction was performed in a two-phase (water-oil) system, without any surfactant. The phase behavior of the microemulsion system in the presence and in the absence of the reactants, and the temperature effects on the phase behavior were investigated. Addition of the hydrophilic reactant, the PEG dihydrazide, to the aqueous component, as well as addition of the hydrophobic aldehyde to the oil, resulted in a reduction of the temperature range of the microemulsion which was interpreted as being due to a change of the spontaneous curvature of the surfactant monolayer in the direction of increased bending towards water. The reaction kinetics were investigated by 1H-NMR. It was shown that the reactions performed in the oil-in-water microemulsion and the liquid crystalline phase were very rapid with almost all of the starting materials being consumed after a 20-min reaction time. The reaction performed in the two-phase system was very slow and after 6 h only 10% of the starting material had reacted.

  • 36.
    Johansson, B
    et al.
    YKI – Ytkemiska institutet.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Alexandrova, L
    Flotation de-inking studies using model hydrophobic particles and non-ionic dispersants2000In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 170, p. 217-229Article in journal (Refereed)
    Abstract [en]

    A series of non-ionic surfactants (alcohol ethoxylates, C10-14E6-8) with HLB within the range of 11.1 to 13.1 were used as dispersants during flotation of mondisperse hydrophobized silica particles (representing ink particles) in deinking formulations. Laboratory scale flotation experiments, contact angle, dynamic surface tension and thin film drainage experiments were carried out. These results indicated that the non-ionic surfactant with the highest CMC (C10E6) gave (a) the highest rate of adsorption at the air/solution interface (b) the lowest reduction in contact angle and (c) the lowest flotation efficiency at concentrations above the CMC. However, below the CMC for C10E6 the flotation efficiency was very high probably due to a low amount of adsorbed material at the particle/solution interface. It was also observed that flotation occurred, in spite of the fact that thin-film measurements indicated that the adsorption of non-ionic surfactants at the air/solution and silica/solution interfaces reduced the hydrophobicity of the particles, as indicated by an increase in stability of the aqueous thin film between the particle and air bubble. This result suggests that the bubble/ink particle capture mechanism (occurring through rupture of the thin aqueous film separating the interfaces) is not the only mechanism controlling the flotation efficiency and that other parameters (such as the kinetics of surfactant adsorption, foaming characteristics and bubble size) need to be taken into account. The kinetics is important with respect to the rate of adsorption of surfactant to both interfaces. Under equilibrium conditions, this may give rise to repulsive steric forces between the air bubble and the particles (stable aqueous thin film). However, at lower adsorption levels (caused by slow adsorption rates) the lower steric repulsion will allow effective collection of particles by the bubble. Also, it was suggested that the influence of alcohol ethoxylates on bubble size could effect the particle capture rate and mechanical entrainment of particles in the froth will also play a role in the flotation recovery.

  • 37.
    Kapilashrami, A
    et al.
    YKI – Ytkemiska institutet.
    Eskilsson, K
    YKI – Ytkemiska institutet.
    Bergström, L
    YKI – Ytkemiska institutet.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Drying of oil-in-water emulsions on hydrophobic and hydrophilic substrates2004In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 233, p. 155-161Article in journal (Refereed)
    Abstract [en]

    We have investigated the effect of the hydrophobic/hydrophilic character of the substrates on the drying behaviour of dilute silicone oil-in-water (o/w) emulsions by light microscopy and ellipsometry. The poly(dimethylsiloxane) (PDMS) emulsion droplets, which are stabilised by a triblock PEO/PPO/PEO copolymer, form a close-packed structure containing domains of hexagonally packed droplets on the hydrophilic substrate. We find that the hydrophilic substrate does not destabilise the emulsion droplets; the close-packed structures are very stable and coalesce very slowly only when most of the water has evaporated. This is supported by ellipsometry measurements, which showed that the emulsion droplets do not adsorb to the hydrophilic substrate. The hydrophobic substrate, on the other hand, destabilises the emulsion and we observed a significant increase in the coalescence rate. Ellipsometry measurements suggest that destabilisation is promoted by the strong interaction between the emulsion droplets and the hydrophobic substrate. We also find that the emulsion undergoes dewetting followed by a release of oil and rewetting of the substrate when the o/w emulsion film reaches a critical thickness on the hydrophobic substrate

  • 38. Kapilashrami, A
    et al.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Eskilsson, K
    YKI – Ytkemiska institutet.
    Benjamins, J-W
    YKI – Ytkemiska institutet.
    Nylander, T
    Ellipsometric studies of nonionic copolymers adsorbed at the solid/water and oil/water interfaces2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 225, p. 181-192Article in journal (Refereed)
    Abstract [en]

    We report on the interfacial behaviour of a series of nonionic diblock copolymers at solid hydrophobic and hydrophilic surfaces/water and silicone oil/water interfaces, studied by ellipsometry. The polymers consist of a hydrophobic C18 chain linked to a hydrophilic poly(ethylene oxide) (PEO), block varying from 50 to 250 U. The adsorption of these copolymers at low bulk concentrations was found to be dominated by the PEO block at all interfaces. At higher concentration the copolymer forms surface aggregates at the silica surface whereas we observe a gradual increase in the adsorbed layer thickness with increased surface excess at the solid hydrophobic surface, indicating a transition from a flat conformation to brush-like layer structure. The results indicate a similar evolution in adsorbed amount with concentration at the silicone oil/water interface as at the hydrophobic silica surface. The influence of the rheological properties of the interface on the adsorption of the diblock copolymer was investigated by comparing results from two silicon oils with different viscosities. The copolymers were found to have stronger affinity to a low viscosity (990 mPa s) silicone oil than to a higher viscosity (12800 mPa s) silicone oil and the hydrophobised silica surface. At the silicone oil/water interface the adsorption of a commercial nonionic triblock copolymer was furthermore investigated and compared with the diblock copolymers

  • 39. Koivula, H.
    et al.
    Kamal Alm, H.
    RISE, Innventia.
    Toivakka, M.
    Temperature and moisture effects on wetting of calcite surfaces by offset ink constituents2011In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, no 3, p. 105-111Article in journal (Refereed)
  • 40.
    Kugge, C
    et al.
    YKI – Ytkemiska institutet.
    Craig, VSJ
    Daicic, J
    YKI – Ytkemiska institutet.
    A scanning electron microscope study of the surface structure of model paper coatings2004In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 238, p. 1-11Article in journal (Refereed)
    Abstract [en]

    We investigate the structure of model paper coating layers, composed of mineral pigments, latex binders and polymeric thickeners and dispersants, using Scanning Electron Microscopy (SEM). The main aim of the study is to identify how systematic variations in the composition of the coating, including pigment type (calcium carbonate, clay), the glass transition temperature of the binder, type (CMC, EHEC) and molecular weight of the polymeric thickener affect the surface features of the coating layer, including surface roughness and porosity and, consequently, gloss. The samples are investigated mainly in conventional high-vacuum SEM mode; however some studies are also performed with the environmental feature (ESEM mode) at higher pressures and humidities, in order to track dynamic changes drying and rewetting. The results are compared to those of recent measurements on the same systems obtained with Atomic Force Microscopy (AFM), where the local latex film formation process has been carefully studied

  • 41.
    Larsson, A
    et al.
    Max-Planck-Institute for Colloids and Interfaces, Germany; 874882.
    Kuckling, D
    Institute for Macromolecular and Textile Chemistry, Germany.
    Schönhoff, M
    Max-Planck-Institute for Colloids and Interfaces, Germany.
    1H NMR of thermoreversible polymers in solution and at interfaces: The influence of charged groups on the phase transition2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 190, p. 185-192Article in journal (Refereed)
    Abstract [en]

    The phase transition of thermoreversible polymers occurring at the lower critical solution temperature (LCST) is investigated by 1H NMR. Poly-N-isopropylacrylamide (PNIPAM) shows such a coil to globule transition at 32°C in aqueous solution. To study the effect of charged polymer segments on the phase transition, the temperature dependent properties of PNIPAM and of a charged PNIPAM-copolymer, containing 10% carboxylic groups, are investigated in solution. Experiments are performed by 1H spectra and PFG-NMR diffusion measurements at different polymer concentrations. The 1H liquid signal is sharply decreasing at the phase transition temperature. The transition is found to be equally sharp for the copolymer as for the homopolymer at concentrations below and around the overlap concentration, whereas the transition is broadened at higher concentrations. Diffusion measurements prove that the conformation of the polymer coils is maintained with increasing temperature until close to the phase transition, apart from a minor decrease of the hydrodynamic radius at about 2°C below the LCST. All data indicate identical phase transition properties of the copolymer as compared with the homopolymer. The introduction of charged groups (3% of monomers dissociated) has thus not altered the transition. Therefore, the copolymer is a suitable candidate for exhibiting a phase transition under electrostatic coupling conditions in layers. Both polymers are adsorbed to colloidal silica (Cab-O-Sil) and investigated by 1H NMR in order to monitor the phase transition in the restricted geometry of an adsorption layer. The liquid 1H intensities of both polymers are decreasing with temperature, this is interpreted as a phase transition of the loops and tails. The transition is substantially broader than in solution, especially at low surface coverage. Significant differences between the copolymer and the homopolymer are observed, since above the transition temperature a liquid signal from loops and tails of the copolymer is still observed. This is interpreted as a comparatively mobile arrangement of the copolymer layer, arising from electrostatic repulsion from the surface and between polymer segments, which is partly hindering globule formation.

  • 42. Lif, A
    et al.
    Holmberg, K
    YKI – Ytkemiska institutet.
    Chemical and enzymatic ester hydrolysis in a Winsor I system1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 130, p. 273-277Article in journal (Refereed)
    Abstract [en]

    Alkaline and lipase catalyzed hydrolysis of 4-nitrophenyldecanoate have been performed in a Winsor I type microemulsion. The reaction occurred in the lower phase oil-in-water microemulsion. After completed reaction a Winsor I ---> III transition was induced by raise in temperature. The products formed, 4-nitrophenol and decanoic acid, partitioned into the upper oil phase and could easily be obtained by separation of this phase and evaporation of the solvent. Surfactant and enzyme (in the case of lipase catalyzed reaction) resided in the middle phase microemulsion and could be reused.

  • 43.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Studies of serum protein adsorption at phospholipid surfaces in relation to intravenous drug delivery1999In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 159, p. 77-87Article in journal (Refereed)
    Abstract [en]

    The adsorption of serum proteins at phospholipid surfaces was investigated in relation to uptake of intravenously administered colloidal drug carriers. In particular, an approach based on the use of surface-modified flat substrates for investigations of the adsorption pattern by in situ ellipsometry and surface plasmon resonance is discussed. Similar results regarding protein adsorption were obtained for phosphiolipid layers prepared through spin-coating, Langmuir-Blodgett deposition, and liposome adsorption. Furthermore, a good agreement was found between the adsorption at the model surfaces, on one hand, and at oil-in-water emulsion droplets, on the other, suggesting that curvature effects on the adsorption are minor. By the use of this approach, the adsorption of a number of proteins at a range of surfaces was investigated. Also mixed (phospho)lipid layers were studied, as was the adsorption from diluted serum and plasma. The results obtained are discussed in relation to the effects of the surface properties on the performance of colloidal drug carriers.

  • 44. Malmsten, M
    et al.
    Tiberg,
    YKI – Ytkemiska institutet.
    Lindman, B
    Holmberg, K
    YKI – Ytkemiska institutet.
    Effects of solvency on the interfacial behaviour in aqueous non-ionic polymer systems1993In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 77, p. 91-100Article in journal (Refereed)
    Abstract [en]

    The effects of solvency on the interfacial behaviour of non-ionic ethylene oxide-containing polymers have been investigated. In particular, ethyl(hydroxyethyl)cellulose (EHEC) and poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) copolymers were considered. Both these types of polymers adsorb at a variety of interfaces. On worsening the solvency, e.g. by increasing the temperature or adding cosolutes which lower the cloud point of the polymer solution, there is a concomitant tendency to increase the adsorbed amount and decrease the adsorbed layer thickness. The outcome of the competition, however, depends on for example, the relative increase in the adsorbed amount. Thus, if the adsorbed amount increases strongly on worsening the solvency, the contraction of the adsorbed layer may be masked, and the adsorbed layer thickness may increase with increasing temperature. If the adsorbed amount is kept constant, however, the only effect of worsening the solvency is a contraction of the adsorbed layer. The forces between polymer-coated surfaces also display a strong solvency dependence. Thus, under good solvency conditions, the interaction force is monotonically repulsive, whereas in poor solvents, an attractive region appears in the force-distance curve. Finally, the solvency-dependent adsorption and interaction properties of these polymers strongly affect their performance, for example, as steric stabilizers or surface modifiers.

  • 45. Manev, E
    et al.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Frother/collector interactions in thin froth films and flotation1993In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 70, p. 289-295Article in journal (Refereed)
    Abstract [en]

    Thin aqueous equilibrium film studies and surface tension measurements on a mixed surfactant system consisting of polyethylene oxide (a model frother) and potassium ethyl xanthate (a model collector) enable the interaction between the two surfactants at the air/solution interface to be elucidated. For the film containing the non-ionic frother, the interface was charged and addition of low concentrations of xanthate acted as a common electrolyte and reduced the thickness of the film inducing rupture. However, at high xanthate collector concentrations, the negative charge xanthate was found to interact with the non-ionic and caused a buildup of negative charge at the air/solution. Higher frother concentrations were necessary to produce non-rupturing thin films upon increasing the xanthate concentration.

  • 46. Mohlin, K.
    et al.
    Loren, Niklas
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
    Nyden, M.
    Water pores in alkyl ketene dimer (AKD) dispersions studied by NMR diffusometry and optical microscopy2007In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 297, no 42007, p. 114-121Article in journal (Refereed)
    Abstract [en]

    Water borne alkyl ketene dimer (AKD) dispersions have been investigated by means of optical microscopy and NMR diffusometry (NMR-D). In two different formulations, different amounts of entrapped water in pores with different sizes are obtained, which can be compared to a water-in-oil-in-water (w/o/w) dispersion. It is shown that the amount of entrapped water inside the AKD particles can conveniently be measured with the NMR-D technique. The pore size is however not obtained correctly from the NMR-D experiment. Due to the small size of the water pores, the pore size is underestimated when measured with NMR-D. This effect is investigated in more detail by Brownian dynamic simulations from which a correction factor is obtained that allows a more correct value of the pore size from NMR-D measurements. When the pore size is too small to be observed by optical microscopy, typically below 0.5 ?m, NMR diffusometry combined with Brownian dynamic simulations are shown to be a rapid and reliable tool for quantifying the porosity in these types of systems. © 2006 Elsevier B.V. All rights reserved.

  • 47.
    Mok, Alberta
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Controlled release of microencapsulated 2-n-octyl-4-isothiazolin-3-one from coatings: Effect of microscopic and macroscopic pores2014In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 458, no 1, p. 155-167Article in journal (Refereed)
  • 48. Naderi, A
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Bergström, M
    Dèdinaitè, A
    YKI – Ytkemiska institutet.
    Trapped non-equilibrium states in aqueous solutions of oppositely charged polyelectrolytes and surfactants: effects of mixing protocol and salt concentration2005In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 253, p. 83-93Article in journal (Refereed)
    Abstract [en]

    The very slow equilibration time in oppositely charged systems makes it necessary to control not only the concentration of the species but also the details of the mixing process. This has been demonstrated for processes occurring at interfaces where order of addition effects can be of great importance. In this investigation we set out to study the bulk properties of aqueous mixtures of a highly charged cationic polyelectrolyte mixed with an anionic surfactant with the aim to learn if long-lived non-equilibrium states were formed also in this case, and thus if the details of the mixing procedure would affect the structure of the aggregates formed. For simplicity we chose two mixing protocols, denoted “PTS” and “STP”. In the PTS-method the polyelectrolyte is added to the surfactant solution whereas in the STP-method the surfactant is added into the polyelectrolyte solution. The properties of the mixtures in aqueous solutions, with different NaCl concentrations and as a function of time, were followed by conducting turbidity, electrophoretic mobility and dynamic light scattering measurements. The results demonstrate that the mixing protocol indeed has a great impact on the size of the aggregates initially formed and that this size difference persists for long times. Hence, trapped non-equilibrium states do play an important role also in the bulk solution. We found that in excess surfactant solutions the smaller aggregates formed by the STP-method are more resistant than the larger ones formed by the PTS-method to colloidal instability induced by electrolytes (NaCl). Based on our results we suggest that for producing small and stable polyelectrolyte–surfactant aggregates in systems with excess surfactant, the surfactant should be added last, while the opposite should be applied for systems with excess polyelectrolyte.

  • 49.
    Nuzzo, Marine
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor. Lund University, Sweden.
    Sloth, Jakob
    GEA Process Engineering A/S, Denmark.
    Brandner, Birgit
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Bergenstahl, Björn
    Lund University, Sweden.
    Millqvist-Fureby, Anna
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor.
    Confocal Raman microscopy for mapping phase segregation in individually dried particles composed of lactose and macromolecules2015In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 481, p. 229-236Article in journal (Refereed)
    Abstract [en]

    The quality of powder is determined by its functionality such as dissolution, encapsulation and flowability. The functionality of powder is in turn determined by their primary properties such as morphology and composition which need to be studied. Hence morphology and surface composition has been largely investigated in spray dried powders and individually dried particles. On the contrary, there is only scarce information regarding the internal structure. With the aim of acquiring a better understanding of the localization of different ingredients in spray dried powders we have used confocal Raman microscopy to investigate the internal microstructure of individually dried particles. In this study three different macromolecules have been investigated: bovine serum albumin, hydroxypropyl methyl cellulose, and triblock co-polymer poloxamer in a lactose matrix are compared at various macromolecule to lactose ratios. The surface and internal component distribution in response to the macromolecule concentration has been established. For the first time phase segregation in particles during a short drying time range is shown. Macromolecules were enriched at the surface of the dried particles and a macromolecule depleted layer was observed below the surface. Macromolecule enriched domains were found segregated from the amorphous lactose matrix in the internal part of the particles. Confocal Raman microscopy was found to be a powerful tool for internal mapping in individually dried particles.

  • 50. Oh, S-G
    et al.
    Kizling, J
    YKI – Ytkemiska institutet.
    Holmberg, K
    YKI – Ytkemiska institutet.
    Microemulsions as reaction media for synthesis of sodium decyl sulfonate II: Role of ionic surfactants1995In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 104, p. 217-222Article in journal (Refereed)
    Abstract [en]

    Synthesis of sodium decyl sulfonate in various types of microemulsions based on nonionic surfactants have been reported in our previous paper. As a continuation of this study the effect of ionic surfactants with different counterions on the reaction profile was investigated. As expected, the electrical potential of microemulsion droplets significantly influenced the degree of conversion probably by affecting the diffusion of ionic species into the interfacial region where the reaction occurs. The reaction yield was also highly dependent on the type of counterions. Tetradecyl trimethyl ammonium acetate increased the yield, but sodium dodecyl sulfate and tetradecyl trimethyl ammonium bromide gave decreased conversion. The counterion effect was explained by the competitive association of ions with the surfactant monolayer at the oil/water interface.

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