The effects of ionic strength and multivalent metal ions on the flocculation performance in Escherichia coli cell disintegrates using the polycationic chitosan as a flocculant were investigated. The study showed that ionic strength could be used to optimize the selectivity in flocculation. The best selectivity was obtained at 0.5 M sodium chloride where 95% of the cell debris and 88% of the nucleic acids could be removed from the disintegrate by sedimentation, leaving 99% of proteins and 86% of -galactosidase enzyme activity in clarified solution. We will also discuss the mechanisms for interaction between chitosan and different groups of components in the disintegrate: cell debris particles, nucleic acid polymers and proteins.

Surfaces coated with poly(ethylene oxide) containing nonionic polymers are of interest in medical applications due to, among other things, the low adsorption of proteins on such surfaces. In this paper we have studied the interfacial properties of surfaces coated with PEO by measuring the forces acting between two such surfaces in water and across a protein solution as well as between one such surface and a surface carrying adsorbed proteins. One type of surface coating was a graft copolymer of poly(ethylene imine) and poly(ethylene oxide) where the cationic poly(ethylene imine) group anchored the polymer to negatively charged mica surfaces. Three different ways to prepare this coating was used and compared. It was found that this coating was not stable in the presence of lysozyme, a small positively charged protein, when the PEO graft density was low. The other type of coating was obtained by adsorbing ethyl(hydroxyethyl)-cellulose onto hydrophobised mica surfaces. The driving force for adsorption is in this case the hydrophobic interaction between nonpolar segments of the polymer and the surface. The EHEC coating was stable in the presence of lysozyme and the interactions between adsorbed layers of lysozyme and EHEC coated surfaces are purely repulsive due to long-range steric forces.

The interactions between human serum albumin (HSA) layers adsorbed from solution onto muscovite mica have been investigated by means of surface force measurements. The effects of varying the ionic strength and the serum albumin concentration have been studied at pH=5.5. The negatively charged protein cannot be desorbed from the negatively charged mica surface by dilution with water. The thickness of the (compressed) adsorbed layer is small compared to the dimension of HSA, except at the highest concentration used (1mg/ml). Hence, under a compressive load at low packing densities the protein conformation on the surface is different from that in bulk solution. No adhesion was observed when the amount adsorbed was large. However, an attractive

In order to obtain a microemulsion that is stable at skin tempeature, the regions of existance of microemulsions of water and isoproptyl myristate were studied as a function of hydrophilelipophile balance (HLB) of nonionic surfactant mixtures. The microemulsion dissolves large amount of the local anaesthetic lidocaine. The amount of dissolved lidocaine in the microemulsion was proportional to the isopropyl myristate content and limited to its solubility in this solvent. The addition of lidocaine lowered the phase inversion temperature (PIT) of the system and increased the temperature range for microemulsion stability. The structure of the microemulsion, as investigated by proton Fourier transform pulsed-gradient spin-echo NMR spectroscopy, was found to be bicontinous. The physico-chemical properties of the microemulsion as well as the low toxicity of its components result in formulation intendend for topical administation.

Several methods of preparing surfaces suitable for interparticle surface forces measurements are presented. Treatment of muscovite mica surfaces with a water vapour plasma introduces surface hydroxyl groups. These groups can react with chlorosilanes to form organo functionalized surfaces. The forces between water vapour plasma treated mica surfaces in aqueous solutions are well described by DLVO theory except for the presence of a short-range (D < 10 Å) additional repulsion. After reaction with a fluorocarbon containing silane the surfaces become hydrophobic and a long-range attraction acts between the surfaces in water. Smooth glass spheres can be obtained by melting a glass rod in a gas burner. These surfaces are ideal substrates for a new type of surface force apparatus that uses a bimorph force sensor for measuring surface forces. The chemistry of the glass surfaces is readily modified by reactions with chlorosilanes. The similarities and the differences between the forces acting between glass and water vapour plasma treated mica surfaces before and after silanation are discussed. We also report on the use of a cold plasma process to produce thin, smooth organic films that can be investigated with the surface force technique.

With this letter, we report how friction can be controlled by inducing physical bonds solely within a polyelectrolyte brush layer, while keeping repulsive interactions between the brush layer and the bare surface that slides above. Our results imply that the nature of the bare surface is of minor importance as long as the repulsive surface interaction is maintained.

With this letter, we report how friction can be controlled by inducing physical bonds solely within a polyelectrolyte brush layer, while keeping repulsive interactions between the brush layer and the bare surface that slides above. Our results imply that the nature of the bare surface is of minor importance as long as the repulsive surface interaction is maintained.

Hydrophobized silica nanoparticles of different sizes, from 16 to 500 nm, were used to impart roughness to a hydrophobic polydimethylsiloxane (PDMS) coating with the aim of obtaining superhydrophobic properties. The particle silanization process and the curing process of the PDMS coating were optimized to increase the contact angle (CA) of the particle containing coating. The evaluation of the coatings, by means of water CA measurements and scanning electron microscopy imaging, shows that superhydrophobicity in the adhesive rose state was achieved using combinations of two differently sized particles, with an excess of the small 16 nm ones. Superhydrophobicity in the lotus state was obtained when the filler concentration of 16 nm particles was 40 wt%, but under such conditions the coating was found to partially crack, which is detrimental in barrier applications. The preference for the rose wetting state can be explained by the round shape of the particles, which promotes the superhydrophobic rose wetting state over that of the superhydrophobic lotus state.

The action of hydrotropes is reviewed emphasizing their influence in the formation of microemulsions, vesicle solutions and other products involving surfactant association structures. It is demonstrated that the hydrotropes, the association structures of which, realistically, can only be described as trivial, actually, are powerful and sophisticated performance chemicals playing an essential role in complex applied formulations utilizing more composite amphiphilic association structures

Nanocomposite coatings are of great interest as barrier coatings since synergy effects between matrix and additive properties can be achieved. This, however, requires favorable additive-matrix interactions to provide a strong interphase (interface region). In this work we elucidate the properties of two environmentally benign nanocomposite coatings based on a waterborne acrylate formulation with additives from renewable sources, i.e. either cellulose nanocrystals, CNC; or, alternatively, cellulose nanofibrils, CNF. We focus on the corrosion protective properties of these coatings and discuss the reason why the nanocomposite with CNC displays favorable corrosion protection properties whereas that with CNF does not. To this end we utilized scanning electron microscopy, water contact angle measurement, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy techniques to investigate the microstructure, surface wetting, interactions between cellulosic materials and matrix as well as corrosion protective properties of both composite coatings.

INTRODUCTION; The Institute for Surface Chemistry - YKI - celebrates its 25th anniversary this year. The Institute, located in Stockholm, Sweden, has played an active part in the development of surface chemistry for various technological applications. The development in this field has been rapid. In the end of the 60's, surface chemistry was a relatively unknown discipline both in academia and in industry; today it is seen as one of the most dynamic areas in chemistry and as a technology of vital importance in industrial branches ranging from pharmaceuticals to paper making. Already in 1962 a laboratory for surface chemistry was founded in Stockholm. The laboratory, headed by Professor Per Ekwall from Finland, grew in size. In 1968, it got the status of an institute. Stig Friberg became the first Director and held the position until 1977. During this period, YKI industrial support was established through the Foundation for Surface Chemistry with members from all Scandinavian countries. The research heritage from Per Ekwall proved fruitful both from a scientific and an applied point of view with active industrial interaction through technical sections in a number of branches. During these years the Institute acquired a solid international reputation. Friberg was succeeded by Ekwall's former student Per Stenius who stayed as Director until 1991. During these years YKI strengthened its positions in several important fields of applied surface chemistry, such as paper making, mineral ore flotation and surface and colloid chemistry related to coatings. An important step on the more fundamental side was the establishment of a research group in the field of surface force measurements. Research in this area has been rewarding and the activity has expanded. The Stockholm group which through the years has maintained close contact with the Canberra group is one of the leading in this field today. YKI today is an institute with a large scientific network all over the world. Active collaboration is maintained with research groups in many countries and the Institute receives a large number of guest scientists each year. What started as a Swedish Institute developing into a Scandinavian organization has now become a truly international operation. Each year YKI arranges an international symposium on applied surface chemistry. This special issue of the lournal of Dispersion Science and Technology contains contributions by invited speakers of this year's meeting, held in Copenhagen, Denmark, in November 1993 and hosted by Novo Nordisk A/S.

The hydrophobic effect is the common expression for processes where nonpolar groups in molecules are spontaneously removed from water. Thermodynamic analysis of hydrocarbon solubility in water, micellization and adsorption of surfactants show that the hydrophobic effect can be understood in terms of two contributions. The first contribution is attributed to the structuring, or rearrangement, of water molecules in the vicinity of a hydrophobe. This contribution is favorable, and hence increases the solubility of hydrocarbons in water, increases the cmc, and decreases the adsorption of surfactants. The second contribution is attributed to the formation of a cavity in the water in order to accommodate the hydrophobe. This contribution dominates over the first one and is unfavorable, i.e. it decreases the solubility of hydrocarbons in water, decreases the cmc, and increases the adsorption of surfactants. Thus, the cause of the hydrophobic effect is to be found in the large energy required to form a cavity in the water. On the other hand the temperature dependence of the hydrophobic effect is entirely determined by the water structuring, or rearrangement, in the vicinity of a hydrophobe.

The interaction between a phospholipid stabilized triglyceride emulsion and a hydrophilic silica surface has been studied at varying pH and electrolyte content using ellipsometry. The adsorbed amount decreases with pH and increases with increasing electrolyte content in the emulsion, and this can be rationalized on the basis of the electrostatic interaction between the emulsion droplet and the surface. The layer thickness, however, is essentially independent of these parameters. In addition, the emulsion has been studied during turbulent shear conditions (applied mechanical stress), with the same variation of pH and electrolyte as in the adsorption experiments. A decrease in pH and an increase in electrolyte content, decreasing the repulsive interaction between the droplets, leads to a deterioration in emulsion stability with time.

The association between a weak cationic linear polyelectrolyte, poly(vinylamine), and the anionic surfactant sodium dodecyl sulfate (SDS) has been investigated in dilute solutions, containing 20 ppm of poly(vinylamine) and surfactant up to a concentration of 8mM. We particularly focus on the importance of the order of addition of the components and of stirring after mixing. Two mixing protocols were used, denoted “PTS” and “STP.” In the PTS method the polyelectrolyte is added to the surfactant solution, and in the STP method the surfactant is added into the polyelectrolyte solution. The results obtained demonstrate the presence of long-lived trapped nonequilibrium states. In addition, we also address the effect of the blending procedure on association. We studied two blending methods, denoted “Blending” and “Vigorous Blending.” In the Blending method equal volumes of the polyelectrolyte and surfactant were added simultaneously to the sample tube, after which the ingredients were mixed together by turning the sample tube upside down a few times; in the Vigorous Blending method the mixing was provided by a magnetic stirrer. The results, obtained using turbidity, electrophoretic mobility, and light scattering measurements, demonstrate that Vigorous Blending facilitates flocculation at low SDS concentrations, close to the charge neutralization concentration of the system. This is interpreted as being due to additional surfactant incorporation in initially positively charged complexes during collision events. Vigorous mixing in excess surfactant produces stable dispersions consisting of small negatively charged complexes containing one polyelectrolyte and surfactant in excess of what is needed to neutralize the polyelectrolyte charges. The same results are obtained with the Blending protocol, which gives comparable particle size and polydispersity in excess surfactant and polyelectrolyte.

Development of multi-purpose probes for mass transport measurements is of importance to gain knowledge in diffusional behaviour in heterogeneous structures such as food, hygiene or pharamceuticals. By combining different techniques, such as Fluorescence Recovery After Photobleaching (FRAP) and Nuclear Magnetic Resonance Diffusometry (NMR-d), information of both local and global diffusion can be collected and used to gain insights on for example material heterogeneities and probe-material interactions. To obtain a FRAP-responsive probe, fluorescent silica particles were produced using fluorescent preconjugates added in a modified Stöber process. A NMR-d responsive moiety was introduced by derivatizing the fluorescent silica particles with polyethylene glycol. The particle size distributions were determined by dynamic light scattering and transmission electron microscopy and these measurements were compared to value extrapolated from diffusion measurements using FRAP and NMR-d. The good agreement between the FRAP and NMR-d measurements demonstrates the potential of multi-purpose probes for future applications concerning mass transport at local and global scale simultaneously. © 2018, © 2018 The Author(s).

Foam generated by sparging of aqueous solutions of the block copolymers P85 (PEO26-PPO39-PEO26), F88 (PEO103-PPO40-PEO103), F127 (PEO99-PPO65-PEO99) and L64 (PEO13-PPO30-PEO13) has been characterized by foam volume and liquid volume measurements as a function of time. Uniform wet foam formed, which, after drainage of the major part of the liquid, transformed to polyhedral dry foam. Conductance jumps across the foam column indicated that structural changes occur at a certain liquid fraction. The dry foams of P85 were less stable than those of F88 and F127. The latter copolymers showed similar foam stability over a period of 1 hour. The L64 foam was very unstable. It is suggested that the stability of the dry foams is determined by the resistance to rupture of the foam films. The foam stability is discussed in relation to earlier studies on the surface rheology and to the thickness of thin foam films. A general relationship for all PEOx-PPOy-PEOx block copolymers between the dilatational modulus and the foam stability could not be found. However, the capability to form thick adsorption layers, accompanied by steric repulsive forces across foam films, appears to be a general foam-stabilizing factor. Surface diffusion coefficients of a fluorescent probe in single block copolymers foam films are also reported for a brief discussion on Gibbs- Marangoni stabilization.

The effect on .beta.-lactoglobulin foam-ability and foam stability of the poly(ethylene oxide)-poly(propylene oxide) block copolymers F127 (PEO99-PPO65-PEO99), mol. wt. 12500 g/mol, and P85 (PEO26-PPO39-PEO26), mol. wt. 4600 g/mol, has been investigated at const. protein concn., 10 .mu.M (0.2 mg/L), and varying block copolymer concns., ranging from 0.02 to 1600 .mu.M. Foam was generated by means of air sparging and the foam vol. and liq. vol. of the foam were measured for one hour. It was found that foam stabilized by F127 or P85 in the concn. range 20-1600 .mu.M contained a larger liq. vol. initially than pure ss-lactoglobulin foam. Furthermore, ss-lactoglobulin foam-ability was only marginally affected by the presence of F127, while it was reduced in an interval of low P85 concns. The protein foam stability was retained in the presence of the larger polymer F127, whereas P85 largely reduced the stability, indicating that the size of the polymeric surfactant is important. The results are discussed in relation to surface rheol. properties and forces acting across foam films. Steric repulsion generated between the surfaces of foam films is suggested to be the main stabilizing factor in dry foam contg. F127. The instability of the mixed ss-lactoglobulin/P85 system is suggested to be caused by two effects. First, there are incompatible stabilization mechanisms of block copolymer and protein, as supported by previous surface rheol. data. Second, there is a reduced importance of long-range steric repulsion when P85 is added, compared to the case where F127 and ss-lactoglobulin are mixed.

The influence of storage conditions on the sizing degree of AKD and ASA sized pilot papers was evaluated. A number of pilot papers sized with AKD or ASA were prepared from ECF bleached pulp fibers, unfilled and filled with 20% PCC, respectively and investigated in terms of sizing degree over a period of several months. The papers were stored at 23 C and 50% RH either wrapped in aluminium foil or as separate sheets exposed to open atmosphere. The unfilled papers stored protected from ambient atmosphere after papermaking showed only a marginal reduction in sizing during prolonged storage. Only the paper having the lowest AKD-dosage suffered from reduced water-resistance, the Cobb60-value changed from 34 to 79 g/m2. The PCC filled papers stored in the same conditions lost some of their sizing, to a higher extent in the case of AKD than for ASA sized papers. This was attributed to the further hydrolysis of the size catalyzed by PCC. In comparison, the sizing of the papers stored as separate sheets dropped significantly even after a few weeks in storage. In the end of the storage the AKD papers, particularly the unfilled ones had lost their sizing efficiency to a clearly higher extent than the ASA papers. The reduction in the sizing level occurred mainly during the first five weeks for the unfilled ASA and AKD papers, after which the process continued at a slower rate. The ToF-SIMS analysis revealed that both AKD and hydrolyzed AKD, the latter being the major portion, were present at the outermost surface of the unfilled AKD sized papers, but in significantly lower levels than in the case of the corresponding protected papers. In other words, a significant loss of AKD mass had occurred for the papers exposed to an open atmosphere. This was attributed to migration of AKD. The results demonstrated that ASA sized papers also suffered from size loss. The ToF-SIMS results showed no signal for active, nonbonded ASA and instead clear signals were observed for hydrolyzed ASA and for calcium and aluminium. As in the papers wrapped in aluminium foil, ASA was mainly in its hydrolyzed form. Although to a markedly lower extent, the reason for sizing loss in the case of ASA was the same as for AKD.

Sterically stabilized polyelectrolyte complexes with stoichiometric composition between oppositely charged synthetic polyelectrolytes carrying strong ionic groups and significantly different molecular weights have been prepared. Poly(sodium styrenesulfonate) (NaPSS) was used as polyanion and a range of brush copolymers with various molar ratio (X = 1, 0.75, 0.5, 0.25) of the poly-methacryloxyethyl trimethylammonium chloride poly(METAC) and the nonionic poly (ethylene oxide) methyl ether methacrylate poly(PEO45MEMA) were used as polycations. Formation and stability of PECs have been investigated by dynamic and static light scattering (LS), turbidity and electrophoretic mobility measurements as a function of polyelectrolyte solution concentration and charge density of the cationic polyelectrolyte. The data obtained suggest that the PEO45- rich systems, NaPSS/PEO45MEMA:METAC-25 and NaPSS/PEO45MEMA: METAC-50, form small, water-soluble, molecular complexes having nonspherical shape. The PEO45-poor NaPSS/PEG45MEMA:METAC-75 form turbid colloidal dispersions, whereas insoluble PECs were revealed for the PEO45-free NaPSS/METAC system. The aggregation level of the PEO45-poor systems is mainly controlled by the concentration of the component solutions used for the preparation of PECs, whereas the aggregation of PEO45-rich nanoparticles is prevented by means of steric stabilization. Electrophoretic mobility data indicate a close to charge neutral state of the generated polyelectrolyte complexes.

Submicron organic particles are produced by precipitation in an emulsion. The poorly water soluble organic substance is dissolved in a non-polar solvent. This solution is dispersed in an aqueous phase in the presence of emulsifier. When the non-polar solvent is removed by evaporation, the organic substance precipitates and one particle is formed in each emulsion droplet. Experimental work are here reported on the rate and the influence of the evaporation rate on the formation of cholesteryl acetate particles. An introductory theoretical analysis of the conditions experienced by each droplet during the evaporation is given. The experimental results suggest that the evaporation of the solvent is a rapid process mainly determined by the transport of the droplets to the vicinity of the air water interface. However, the results also show that the size of the particles formed by precipitation in the emulsion, is insensitive to the evaporation conditions, for instance if the evaporation is artificially slow. The particle size is mainly governed by the size of the emulsion droplets. The analysis discuss the possibility that during the evaporation of the emulsion, each individual droplet is emptied of its content of the non-polar solvent very rapidly. The hypothesis that each solid particle is formed during a very short period of time without obtaining a concentration equilibrium within the droplet is tested. However, the order-of-magnitude estimations do not support a kinetic explanation for the fact that the particles obtain the size of the emulsion droplets.

Lipase catalyzed hydrolysis of a triglyceride, palm oil, was performed in L2 type microemulsions based on different surfactants. Isooctane was used as hydrocarbon and the composition of the microemulsions was the same in all experiments. NMR self-diffusion measurements indicated that all microemulsions consisted of closed water droplets and that the structure did not change much during the course of the reaction. The hydrolysis was fast in the microemulsions based on branched-chain anionic or nonionic surfactant but very slow when a branched cationic or a linear nonionic surfactant was used. The cationic surfactant was found to form aggregates with the enzyme. No such interactions were detected with the other surfactants.

Polyelectrolyte multilayers are receiving much attention due to their insolubility and due to structural responses induced in them by changes in solution properties such as, for example, temperature, pH or ionic strength. These characteristics make polyelectrolyte multilayers highly interesting in encapsulation technology and controlled delivery applications. However, producing dry, biocompatible formulations for storage of low molecular weight substances poses a challenge. One possibility is to make use of a well-defined mesoporous inorganic carrier material as host for the model substance (in our case ibuprofen). Control over release properties are enabled by polyelectrolyte encapsulation of the inorganic carrier. We built such multilayers through consecutive deposition of PAH and PSS on top of a first layer ofr PEI. These layers were adsorbed either in presence or absent of ibuprofen. The influence of long time storage, 2 years, of the samples was also investigated. The polyelectrolyte multilayer structure was investigated in detail by Dual Polarization Interferometry (DPI), and we use these data to interpret the measured release profiles.

The interactions at the air/liquid and the liquid/solid interface have been studied for octyl ß glucoside. With the thin film balance the thickness of the equilibrium liquid films is determined as a function of surfactant concentration, inert salt concentration and pH. At high surfactant concentration and/or at low. pH black films, about 4.6 nm thick, are formed. The stabilizing forces in the black films are related to the interactions within and between the layers. The forces acting between octyl-ß-glucoside surfactant layers adsorbed on hydrophobized mica were investigated with the interferometric type surface force apparatus. The forces measured between the sugar head-groups were similar to those acting between other small nonionic groups like dimethylamine oxide and monoglycerides. However, considerably more long-range repulsions are observed between surfactants with oligoethylene oxide head-groups.

In the present paper, magnetic contribution on the aggregation of some magnetic mineral particle ultrafines were studied. There are two different magnetic properties that may enhance particle aggregation: a) field-induced magnetic moment; and b) magnetic moment due to the remanent magnetisation. The magnetic field-induced aggregation of the oxide mineral particle ultrafines (hematite and chromite) in aqueous suspension at moderate ionic strenght was investigated using a labortory scale electromagnetic solenoid. The experimental results relate the aggregation process (as determined by magneto-sedimentation analysis) to particle size and the external magnetic field in the antural pH value of the dispersions by using a modified form of the DLVO theory. In cases where the electrostratic repulsion was not suppressed, then the long range magnetic forces enabled aggregation to occur in the "secondary minimum" potential energy sink. This caused the formation of chains/rings, which appeared to be relatively stable at enhanced rates of settling. It is indicated in this paper that hematite ultrafines in a well-dispersed slurry are selectively aggregated with sized magnetite in the absence of aggregating reagents, high shear rates or an external magnetic field. The formation of aggregates is attributed to the presence of the remanent magnetisation in these oxide iron minerals, aminly in the magnetite.