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  • 2051.
    Bergström, Jenny
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    This is the air we breathe ...2007Conference paper (Refereed)
    Abstract [en]

    'This is the air we breathe ... ' are posters designed for raising awareness. They present continuous feedback on our urban environment and the effects of traffic. Using flock printing, a dirt-absorbing text or pattern is printed on a less dirt-absorbing surface in order to create a slow but direct response to pollution. Drivers are reminded of their impact on the city, which is also visible to others passing by. This project embraces complexity, making a problematic and abstract issue local and tangible.

  • 2052.
    Bergström, Jenny
    et al.
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Clark, Brendon
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Frigo, Alberto
    SWITCH!.
    Mazé, Ramia
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Redström, Johan
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Vallgårda, Anna
    SWITCH!.
    Becoming materials: Material forms and forms of practice2010In: Digital Creativity, ISSN 1462-6268, E-ISSN 1744-3806, Vol. 21, p. 155-172Article in journal (Refereed)
    Abstract [en]

    As a result of development toward ‘smart’ materials, materials now enable an expanding range of aesthetic expressions and user experiences. These materials are fundamentally temporal in their capacity to assume multiple, discrete states of expression that can be repeatedly and minutely controlled. These materials come to be, or become, only over time and in context—they are becoming materials. Thus, in the development and application of such materials, we must engage more extensively with the experience of materials in practices of design and of use. This paper introduces and discusses the concept of becoming materials—as well as the implications for practice—through a series of examples from our own practice-led research within art, design and architecture. Coming to terms with the implications for material practices of design and of use, we suggest, requires the development of new concepts and methods for doing and studying the design of becoming materials.

  • 2053.
    Bergström, Jenny
    et al.
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Clark, Brendon
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Frigo, Alberto
    SWITCH!.
    Mazé, Ramia
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Redström, Johan
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Vallgårda, Anna
    SWITCH!.
    Telltale2013In: SWITCH! Design and everyday energy ecologies, Stockholm, Sweden: Interactive Institute Swedish ICT , 2013, 15, p. 101-132Chapter in book (Other academic)
    Abstract [en]

    'Telltale' is a piece of furniture that collects traces of energy (mis)use. Connected remotely to a household’s electricity meter, it responds to increases or decreases in energy consumption. Increases cause its internal structure to become less robust and, when used in weakened states, its textile surface becomes prone to flaking, crackling and wrinkling. Telltale decomposes more or less quickly — users participate in the (de)formation of an object that tells them about themselves, others and the cumulative effect of local actions. A prototype has been built and studied within two households — alterations in household actions as well as family interactions were prompted by Telltale, evolving as the object changed over time in use.

  • 2054.
    Bergström, Jenny
    et al.
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Mazé, Ramia
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Redström, Johan
    RISE, Swedish ICT, Interactive Institute. Design Research Unit.
    Vallgårda, Anna
    SWITCH!.
    Jeczmyk, Olivia
    SWITCH!.
    Bildinstitutet,
    SWITCH!.
    Symbiots2013In: SWITCH! Design and everyday energy ecologies, Stockholm: Interactive Institute Swedish ICT , 2013, 17, p. 159-200Chapter in book (Other academic)
    Abstract [en]

    ‘Symbiots’ imagines forms in the urban landscape that operate parasitically — emerging and thriving when households or neighborhoods reduce energy consumption. For people, the provision of these as public functions acts as a reward. For Symbiots, it lures people away from their private habitats and energy-consuming habits, thus leaving more power for others in the electricity grid. The project queries increasing competition for natural resources and current human- (versus eco-) centered design paradigms. Symbiots takes the form of a photo series in the genre of contemporary hyperreal art photography. Produced as posters, these have been the basis for raising awareness and discussions with neighborhood residents.

  • 2055.
    Bergström, K
    et al.
    Berol Nobel, Sweden.
    Holmberg, K
    YKI – Ytkemiska institutet. Berol Nobel, Sweden.
    Microemulsions as reaction media for immobilization proteins to hydrophilized surfaces1992In: Colloids and Surfaces, ISSN 0166-6622, E-ISSN 1873-4340, Vol. 63, p. 273-280Article in journal (Refereed)
    Abstract [en]

    The effect of microemulsion as reaction medium for immobilization of proteins to polystyrene hydrophilized with poly(ethylene glycol) or polysaccharide has been investigated. The amount of albumin, immunoglobulin G (IgG) and collagen immobilized from microemulsion was increased 10-100 times, compared with immobilization from an aqueous buffer system. The stability of anti-IgG and interleukin-2 was studied in different microemulsion systems. Anti-IgG was found to be stable in microemulsions based on sodium bis(2-ethylhexyl)sulphosuccinate (AOT) and C12EO5, whereas the non-ionic surfactant di-C9EO9 almost instantly destroyed the antigen-binding properties. Interleukin-2 completely lost its biological activity in an AOT-based microemulsion. We have also found that the choice of microemulsion influences coupling efficiency of the protein. An AOT-based system is preferred for immobilization of mycoplasma antibody, while a microemulsion based on C12EO5 is preferred for borrelia antigen.

  • 2056.
    Bergström, Karl
    et al.
    RISE, Swedish ICT, Interactive Institute. GAME.
    Björk, Staffan
    RISE, Swedish ICT, Interactive Institute. GAME.
    Lundgren, Sus
    Exploring Aesthetic Gameplay Design Patterns – Camaraderie in Four Games2012Conference paper (Refereed)
    Abstract [en]

    This paper explores how a vocabulary supporting design-related discussions of gameplay preferences can be developed. Using the preference of experiencing camaraderie as an example, we have analyzed four games: the board games Space Alert and Battlestar Galactica, the massively multiplayer online game World of Warcraft, and the cooperative FPS series Left for Dead. Through a combination of the MDA model on how game mechanics give rise to game aesthetics via game dynamics, and the concept of aesthetic ideals in gameplay, we present gameplay design patterns related to achieving camaraderie. We argue that some of these patterns can be seen as aesthetic gameplay design patterns in that they are closely related to aesthetic ideals. Further, as a consequence, gameplay design pattern collections which include patterns related to all levels of the MDA model can be used as design tools when aiming for certain gameplay aesthetics.

  • 2057.
    Bergström, Karl
    et al.
    RISE, Swedish ICT, Interactive Institute. GAME.
    Jonsson, Staffan
    RISE, Swedish ICT, Interactive Institute. GAME.
    Björk, Staffan
    RISE, Swedish ICT, Interactive Institute. GAME.
    Undercurrents – A Computer-Based Gameplay Tool to Support Tabletop Roleplaying2010Conference paper (Refereed)
    Abstract [en]

    This paper introduces Undercurrents, a computer-based gameplay tool for providing additional communication and media streams during tabletop roleplaying sessions. Based upon a client-server architecture, the system is intended to unobtrusively support secret communication, timing of audio and visual presentations to game events, and real-time documentation of the game session. Potential end users have been involved in the development and the paper provides details on the full design process.

  • 2058.
    Bergström, L
    YKI – Ytkemiska institutet.
    Characterization of the surface chemistry of silicon nitride powders1994In: Ceramic Transactions: Materials Processing and Design: Grain Boundary Controlled Properties of Fine Ceramics II, American Ceramic Society, 1994, p. 77-87Chapter in book (Refereed)
    Abstract [en]

    Introduction: Silicon nitride is a ceramic material with a potential for high strength at room as well as elevated temperatures, good thermal shock resistance and relatively good oxidation resistance. However, optimal properties can only be realized when the microstructure and the grain boundary composition of the sintered body is controlled. Several studies have shown that the surface properties of the starting powder, together with the choice and addition of sintering aids, play a decisive role in determining the final properties [1-3]. However, the final properties of the sintered material depend on many different parameters. These parameters include the green-body characteristics, the physical and bulk chemical powder properties and the sintering conditions together with the powder surface chemical properties. Hence, it has been difficult to define the relationship between only the surface chemical properties and materials properties more precisely. Also, it is not clear how the relevant surface properties of silicon nitride should be characterized and quantified. This paper is a part of a review on the surface chemistry of silicon nitride [4]. The focus will be on an overview of the methods that are available to characterize relevant surface properties of ceramic powders, together with a summary on the present understanding of the surface chemistry of silicon nitride.

  • 2059.
    Bergström, L
    YKI – Ytkemiska institutet.
    Hamaker constants of inorganic materials1997In: Advances in Colloid and Interface Science, ISSN 0001-8686, E-ISSN 1873-3727, Vol. 70, p. 125-169Article in journal (Refereed)
    Abstract [en]

    Calculations of Hamaker constants using Lifshitz theory require the availability of accurate dielectric data, especially in the ultraviolet spectral region, and the use of a convenient and appropriate mathematical representation. In this review, a multiple oscillator model– the so called Ninham-Parsegian (N-P) representation– has been used and spectral parameters for 31 different inorganic materials (including diamond) have been generated from critically evaluated optical data or collected from the literature. For most materials, a two-oscillator model (one UV and one IR term) was used but more detailed representations were included when available. The spectral parameters presented here can be combined with previous data, mainly focused on hydrocarbon and organic systems, to yield an extensive spectral data base for both solids and liquids enabling Lifshitz calculations of Hamaker constants for many materials combinations. Non-retarded Hamaker constants for symmetric material combinations across vacuum (A1v1) and water (A1w1) have been calculated for the different materials; these calculations were performed using the full Lifshitz theory. Asymmetric combinations, A1v3 and A1w3, against four commonly used materials in atomic force microscopy studies: silica, amorphous silicon nitride, sapphire, and muscovite mica, have also been covered. The use of a new dielectric representation for water resulted in significantly lower values of A1w1 compared to previous calculations. Analytical approximations to the full Lifshitz theory were evaluated and found to give surprisingly accurate results (the Tabor-Winterton approximation) for A1v1 when the IR contribution is of minor importance. An attempt to make the TW approximation more general by establishing some scaling relationship between between n0 and wUV was met with little success; only the UV spectral parameters of the covalent oxides, sulphides and nitrides may be fitted to a simple power law relation. The Lifshitz calculations in this study was compared with an alternative method where a more detailed dielectric representation in the visible-ultraviolet spectral range was obtained through Kramers-Kronig (K-K) transformation of reflectivity data over a broad frequency range. Despite the difference in dielectric information, the two methods generally yield non-retarded Hamaker constants which do not differ significantly. This is not true for all materials, e.g. water, where a more detailed representation using either a N-P representations with several oscillators or the K-K representation must be used. It was shown that the omission of the static and low frequency contribution in the latter method may result in a significant underestimation of the value for A1w1 when the dispersive contribution becomes very small.

  • 2060.
    Bergström, L
    YKI – Ytkemiska institutet.
    Lättflytande som mjölk eller trögflytande som tandkräm1997In: Kemisk Tidskrift/Kemivärlden, ISSN 1650-0725, Vol. 7, p. 57-58Article in journal (Refereed)
  • 2061.
    Bergström, L
    YKI – Ytkemiska institutet.
    Rheological properties of concentrated, nonaqueous silicon nitride suspensions1996In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 79, p. 3033-3040Article in journal (Refereed)
    Abstract [en]

    The rheological properties of nonaqueous silicon nitride powder suspensions have been investigated using steady shear and viscoelastic measurements. The polymeric dispersant, Hypermer KD-3 adsorbed strongly on the powder surfaces and colloidally stable, fluid suspensions up to a volume fraction of Φ= 0.50 could be prepared. The concentrated suspensions all displayed a shear thinning behavior which could be modelled using the high shear form of the Cross equation. The viscoelastic response at high concentrations was dominated by particle interactions, probably due to interpenetration of the adsorbed polymer layers, and a thickness of the adsorbed Hypermer KD-3 layer, ∆≈10 nm, was estimated. The volume fraction dependence of the high shear viscosity of three different silicon nitride powders were compared and the differences, analysed by using a modified Krieger-Dougherty model, were related to effective volume effects and the physical characteristics of the powders. The significantly lower maximum volume fraction, Φm= 0.47, of the SN E-10 powder was referred to the narrow particle size distribution and the possibility of an unfavourable particle morphology.

  • 2062.
    Bergström, L
    YKI – Ytkemiska institutet.
    Rheology of concentrated suspensions1994In: Surface and Colloid Chemistry in Advanced Ceramics Processing / [ed] Pugh, R.J. & Bergström, L., Marcel Dekker, 1994, p. 193-244Chapter in book (Refereed)
    Abstract [en]

    Various aspects of alkyd emulsion technology have been investigated. Firstly, the influence of alkyd oil length, acid value and hydroxyl number, as well as the type of surfactant used as emulsifier, on shear stability of alkyds emulsions have been studied. It was found that the acid value was the most important alkyd parameter, the stability increasing with increasing oil length. It is also shown that anionic surfactants give emulsions with small droplet sizes down at lower concentrations than nonionics. Secondly, polymerizable nonionic surfactants have been tested as emulsifiers and compared with conventional surfactants of the same HLB. It was found that surfactants capable of participating in the autoxidative curing process give faster drying and improved film hardness compared with non-reactive surfactants. Thirdly, the distribution of driers between the alkyd phase and the water phase has been investigated. It was found that low pH and the use of hydrophilic anionic surfactants, such as SDS, favour partitioning of cobalt into the aqueous phase which is unfavourable with respect to drying properties.

  • 2063.
    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.

  • 2064.
    Bergström, L
    YKI – Ytkemiska institutet.
    Surface chemical characterization of ceramic powders1994In: Surface and Colloid Chemistry in Advanced Ceramics Processing / [ed] Pugh, R.J. & Bergström, L., Marcel Dekker, 1994, p. 71-125Chapter in book (Refereed)
  • 2065.
    Bergström, L
    YKI – Ytkemiska institutet.
    Surface chemistry of silicon nitride powders: adsorption from non-aqueous solutions1992In: Colloids and Surfaces, ISSN 0166-6622, E-ISSN 1873-4340, Vol. 69, p. 53-64Article in journal (Refereed)
    Abstract [en]

    The adsorption behaviour in cyclohexane of different silicon nitride powders have been studied. Adsorption isotherms of organic probe molecules covering a wide spectra of Lewis acidity/basicity showed large variation in adsorption behaviour between the different probes. Mathematical analysis showed that the adsorption data could be described by a Langmuir-Freundlich type of isotherm. Using a previously presented model of the silicon nitride surface, it was possible to relate the variation of isoelectric point in water between the three powders to a difference in the relative site density of silanol and amino groups on the surface. It was found that the maximum concentration (M) of benzoic acid increased linearly while M of pyridine decreased with an increase in the relative amount of amino groups on the surface.

  • 2066.
    Bergström, L
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, Trätek..
    Träanvändning inom ROT-sektorn examensarbete i byggnadsteknik1988Report (Other academic)
    Abstract [sv]

    I ett examensarbete visas hur trä används vid förbättring av flerbostadshus. Arbetet presenteras så att tidigare erfarenheter av byggteknik inte ska vara nödvändiga för förståelsen. Väggar, bjälklag, fasader, yttertak, vindar, fönster, snickerier och gårdsmiljö tas upp.

  • 2067.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Probing polymeric stabilization in nonaqueous media by direct measurements2000In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 83, p. 217-219Article in journal (Refereed)
    Abstract [en]

    The steric repulsion induced by adsorbed layers of the commercial dispersant Hypermer KD3 has been probed by direct measurements in decalin. The forces are long range (commencing at 30-40 nm) and repulsive, and the distance dependence can be modeled with a simple scaling theory expression valid for polymer brushes. We obtain layer thicknesses on the order of L~9-15 nm for the compressed layers depending on KD3 concentration while the undisturbed layers have a thickness L~23-24 nm, independent of polymer concentration. Comparision of the measured interaction lengths of compressed and undisturbed polymer layers with previous layer thickness estimates based on rheological studies shows that the polymer layers are compressed in dense suspensions.

  • 2068.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Guldberg-Pedersen, H
    Interparticle forces and rheological properties of ceramic suspensions1999In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 159-160, p. 119-126.Article in journal (Refereed)
    Abstract [en]

    Dispersants have a profound influence on the suspension properties of ceramic slurries. We will illustrate the effect of polymers and polyelectrolytes on the colloidal stability and the rheological properties in both aqueous and non-aqueous media. We have related direct measurements of polymerically induced interparticle forces to the rheological properties of different ceramic systems. Simple estimates of the effective volume fractions of non-aqueous, polymerically stabilized silicon nitride suspensions gave a reasonable correspondence between calculated and measured polymer layer thicknesses. We show that PAA stabilize zirconia by an electrosteric mechanism; also, we found an excellent agreement between the presence of bridging attraction and poor colloidal stability at low surface coverage. In addition, the van der Waals forces have been quantified by theoretical calculations and direct measurements.

  • 2069.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Bostedt, E
    Surface chemistry of silicon nitride powders: electrokinetic behaviour and ESCA studies1990In: Colloids and Surfaces, ISSN 0166-6622, E-ISSN 1873-4340, Vol. 49, p. 183-197Article in journal (Refereed)
  • 2070.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Carlström, E
    Carlsson, R
    Novel ceramic processing methods using responsive polymers1997In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 132-136, p. 12-13Article in journal (Refereed)
    Abstract [en]

    Abstract not available.

  • 2071. Bergström, L
    et al.
    Ernstsson, M
    YKI – Ytkemiska institutet.
    The effect of wet and dry milling on the surface properties of silicon nitride powders1991In: Ceramics Today: Tomorrow's Ceramics / [ed] Vincenzini, P., Elsevier, 1991, p. 1005-1014Chapter in book (Refereed)
    Abstract [en]

    The effects of dry milling in air and wet miling in isopropanol, on the surface properties of silicon nitride powders have been investigated. The ground powders have been analyzed with resoect to oxygen and carbon content, electrokinetic behviour, wetting characteristics and adsorption of acidic and basic probe molecules. The results show that dry milling in air leeds to a higher degree of surface oxidation which is correlated to substantially lower isoelectric points for dry milled vs. wet milled powders. The wet milled powders were contaminated by an adsorbed layer of isopropanol which resulted in an initially hydrophobic behaviour and low levels of adsorption of most probe molecules. This coating can be removed by heat treatment at elevated tempratures.

  • 2072. Bergström, L Magnus
    et al.
    Skoglund, Sara
    Danerlöv, Katrin
    YKI – Ytkemiska institutet.
    Garamus, Vasil M
    Pedersen, Jan Skov
    The growth of micelles, and the transition to bilayers, in mixtures of a single-chain and a double-chain cationic surfactant investigated with small-angle neutron scattering2011In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 7, no 22, p. 10935-10944Article in journal (Refereed)
    Abstract [en]

    Self-assembly in aqueous mixtures of a single-chain (DTAB) and a double-chain cationic surfactant (DDAB) has been investigated with small-angle neutron scattering (SANS). Small oblate spheroidal micelles formed by DTAB grow with respect to width and length to form mixed ellipsoidal tablet-shaped micelles as an increasing fraction of DDAB is admixed into the micelles. The growth behaviour of the micelles is rationalized from the general micelle model in terms of three bending elasticity constants spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant ((k(c)) over bar kc). It is found that micelles grow with respect to width, mainly as a result of decreasing k(c)H(0), and in the length direction as a result of decreasing k(c). The micelles are still rather small, i.e. about 140 angstrom in length, as an abrupt transition to large bilayer aggregates is observed. The micelle-to-bilayer transition is induced by changes in aggregate composition and is observed to occur at a mole fraction of DDAB equal to about x = 0.48 in D2O, which is a significantly higher value than previously observed for the same system in H2O (x = 0.41). An abrupt micelle-to-bilayer transition is in agreement with predictions from the general micelle model, according to which an abrupt transition from micelles to bilayers is expected to occur at xi H-0 = 1/4, where x is the thickness of the self-assembled interface, and we may conclude that H-0(D2O) > H-0(H2O) for the system DDAB/DTAB in absence of added salt. Samples with bilayers are found to be composed of bilayer disks coexisting with vesicles. Disks are found to always predominate over vesicles with mass fractions about 70-90% disks and 10-30% vesicles. Micelles, disks and vesicles are observed to coexist in a few samples close to the micelle-to-bilayer transition.

  • 2073.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Meurk, A
    YKI – Ytkemiska institutet.
    Measuring granule friction and adhesion with an atomic force microscope2002In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 206-213, p. 63-66Article in journal (Refereed)
  • 2074.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Meurk, A
    YKI – Ytkemiska institutet.
    Arwin, H
    YKI – Ytkemiska institutet.
    Rowcliffe, DJ
    YKI – Ytkemiska institutet.
    Estimation of Hamaker constants of ceramic materials from optical data using Lifshitz theory1996In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 79, p. 339-348Article in journal (Refereed)
    Abstract [en]

    The Hamaker constants of 8 different ceramic materials, 6H-SiC, tetragonal, partially stabilized-ZrO2 (3% Y2O3), b-Si3N4, a-Al2O3, Y2O3, sapphire (single crystal a-Al2O3), MgO, MgAl2O4, and fused silica, across air, water, and n-dodecane at room temperature and across silica at 2000 K have been calculated from optical data using Lifshitz theory. Spectroscopic ellipsometry was used to measure the photon energy dependence of the refractive index, n, and the extinction coefficient, k, in the visible and near-UV range on several important ceramic materials. This relatively simple, nondestructive technique has proved to yield reliable optical data on sintered, polycrystalline materials like Si3N4, SiC, ZrO2 and Al2O3. For the other materials, Y2O3, sapphire, MgO, MgAl2O4 and fused silica, optical data from the literature were used to calculate the Hamaker constants. The calculated Hamaker constants were estimated to be accurate within ± 10%.

  • 2075.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Interfacial characterization of silicon nitride powders1989In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 72, p. 103-109Article in journal (Refereed)
  • 2076.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Schilling, CH
    Aksay, IA
    Consolidation behavior of flocculated alumina suspensions1992In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 75, p. 3305-3314Article in journal (Refereed)
    Abstract [en]

    The consolidation behavior of flocculated alumina suspensions was analyzed as a function of the interparticle energy. Consolidation was performed by a centrifugal force field or by gravity and both the time dependent and equilibrium density profiles were measured by a gamma ray absorption technique. The interparticle energy at contact was controlled by adsorbing fatty acids of varying molecular weight at the alumina/decalin interface. We found that strongly attractive interactions result in a particle network which resists consolidation and shows compressible behavior over a large stress range. The most weakly flocculated suspension showed an essentially incompressible, homogeneous density profile after consolidation at different centrifugal speeds. We also found a significant variation in the maximum volume fraction, m, obtained, with m 0.54 for the most strongly flocculated suspension to m 0.63 for the most weakly flocculated suspension. The compressive yield stresses show a behavior which can be fitted to a modified power law. In this paper, we discuss possible correlations between the fitting parameters and physical properties of the flocculated suspensions.

  • 2077.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Shinozaki, K
    Tomiyama, H
    Mizutani, N
    Colloidal processing of a very fine BaTiO3 powder-effect of particle interactions on the suspension properties, consolidation and sintering behavior1997In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 80, p. 291-300Article in journal (Refereed)
    Abstract [en]

    The relation between the suspension state and the rheological properties, the consolidation, and packing of a very fine (nanosized) BaTiO3 powder has been investigated. The BaTiO3 powder was suspended in a non-aqueous medium by adsorbing fatty acids and a polymeric dispersant, poly(12-hydroxy stearic acid), (PHS), at the BaTiO3/decane interface. Calculated interparticle energies implies that the suspension with PHS adsorbed is colloidally stable while the suspensions with oleic and octanoic acid can be characterised as weakly and strongly flocculated, respectively. Analysis of settling experiments and rheological measurements at high concentrations confirmed this characteristics. Pressure filtration resulted in nearly identical green body densities in spite of the differences in colloidal properties, but the preliminary sintering experiments and microstructural characterisation showed that the strongly flocculated suspension displays a significantly retarded sinterability compared to the colloidally stable and the weakly flocculated suspensions. The absence of a correlation between green density and sintering behavior was explained by considering both the volume taken by the adsorbed fatty acids and the PHS polymer-which can be substantial for nanosized powders- and the state of the suspension. While a decrease in the thickness of adsorbed surfactant or polymer layer will enable a higher particle packing density, such a thin adsorbed layer result in a more strongly flocculated suspension which will resist dense packing. Hence, it is suggested that the green bodies of the colloidally stable and the weakly flocculated suspensions correspond to a relatively homogeneous, but loosely packed, green body microstructure. The strongly flocculated suspension results in a green body with a more inhomogeneous microstructure.

  • 2078.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Sjöström, E
    YKI – Ytkemiska institutet.
    Temperature induced flocculation of concentrated ceramic suspensions: rheological properties1999In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 19, p. 2117-2123Article in journal (Refereed)
    Abstract [en]

    Concentrated, sterically stabilised ceramic suspensions have been reversibly flocculated by changing the temperature. Using an amphiphilic polymer, Hypermer KD3, as dispersant for alumina and alumina-silicon carbide whisker composite mixtures in pentanol resulted in a transition from dispersed to flocculated state close to room temperature. The collapse of the adsorbed polymer layer with decreasing solvency (temperature) in the marginal solvent pentanol induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. Temperature induced flocculation (TIF) has a drastic effect on the rheological properties. At high temperatures, T>30 °C, the suspensions have a low viscosity and neglible elasticity. When the temperature is lowered below 20 °C, the viscosity increases significantly and the viscoelastic behaviour becomes predominatly elastic. The elasticity and the associated particle network strength are sufficiently high for a highly concentrated gelled suspension to support its own weight. The potential use of TIF as a novel forming method was discussed with relation to other new shaping techniques.

  • 2079.
    Bergström, L
    et al.
    YKI – Ytkemiska institutet.
    Stemme, S
    Dahlfors, T
    Arwin, H
    Ödberg, L
    Spectroscopic ellipsometry characterisation and estimation of the Hamaker constant of cellulose1999In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 6, p. 1-13Article in journal (Refereed)
    Abstract [en]

    Calculations of Hamaker constants using Lifshitz theory require the availability of accurate dielectric data, especially in the visible-ultraviolet region. We present spectroscopic ellipsometry data on well defined cellulose films of a limited thickness range (100–140 layers) deposited on an oxidised and hydrophobised silicon substrate. The spectral data, representing measurements from a perpendicular orientation to the fibre deposition direction, was used for estimates of the necessary spectral parameters, i.e. the oscillator strengths and characteristic frequencies in the UV-range. Our calculations show that cellulose has a relatively low Hamaker constant in air (58 zJ) and water (8.0 zJ). The implications for the surface energy estimates of cellulose and colloidal interactions between cellulose and various types of fillers and coating colours were discussed.

  • 2080.
    Bergström, Lennart
    YKI – Ytkemiska institutet.
    Colloidal processing of ceramics2002In: Handbook of Applied Colloid and Surface Chemistry / [ed] Krister Holmberg, Chichester; Weinheim: Wiley , 2002, p. 201-218Chapter in book (Refereed)
  • 2081.
    Bergström, Lennart
    YKI – Ytkemiska institutet.
    Från beck till pulverfärg2001In: Med färg i blicken, Uppsala: Ord & Vetande AB , 2001, p. 89-98Chapter in book (Refereed)
  • 2082.
    Bergström, LM
    YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Bending elasticity of nonionic surfactant layers2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 4, p. 1949-1960Article in journal (Refereed)
    Abstract [en]

    A novel approach to evaluate the bending elasticity of monolayers formed by nonionic surfactants with a rigid head group is introduced by means of considering head group repulsion as derived from the free energy of mixing rigid hydrophilic head groups with surrounding solvent molecules as well as contributions related to the hydrophobic tails. Explicit expressions for the spontaneous curvature (H0), bending rigidity (kc) and saddle-splay constant (k̄c) have been derived for the constraint of constant chemical potential of free surfactant (thermodynamically open layers) as well as the constraint of constant aggregation number (thermodynamically closed layers). Most interestingly, it is demonstrated that kc for thermodynamically open layers formed by a nonionic surfactant with rigid tail and head group always must be zero. However, kc for surfactants with a flexible tail as a function of the head group-to-tail volume ratio is found to go through a maximum at some large, positive value of k c and H0 ≈ 0. Eventually, kc falls below zero as the head group volume increases above a certain value. Hence, we may conclude that nonionic surfactants with a rigid head group may form thermodynamically stable fluid layers or aggregates only insofar the hydrophobic part is flexible with respect to chain conformational degrees of freedom and the head group is not too voluminous. It is found that the head group repulsion contribution to kcH0 is always positive whereas the corresponding contribution to k̄c may be positive or negative depending on whether the hydrophobic layer of the film is thicker or thinner than the hydrophilic layer.

  • 2083. Bergström, LM
    et al.
    Bastardo, LA
    YKI – Ytkemiska institutet.
    Garamus, VM
    A small-angle neutron and static light scattering study of micelles formed in aqueous mixtures of a nonionic alkylglucoside and an anionic surfactant2005In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, p. 12387-12393Article in journal (Refereed)
    Abstract [en]

    The size and shape of micelles formed in aqueous mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic sugar-based surfactant n-decyl â-D-glucopyranoside (C10G) at different concentrations of added salt have been investigated with small-angle neutron and static light scattering. Rather small prolate ellipsoidal micelles form in the absence of added salt and at [NaCl] ) 10 mM in D2O. The micelles grow considerably in length to large rods as the electrolyte concentration is raised to [NaCl] ) 0.1 M. In excess of nonionic surfactant ([SDS]/[C10G] ) 1:3) at [NaCl] ) 0.1 M in D2O, several thousands of Ångstroms long wormlike micelles are observed. Most interestingly, a conspicuously large isotope solvent effect was observed from static light scattering data according to which micelles formed at [SDS]/[C10G] ) 1:3 and [NaCl] ) 0.1 M in H2O are at least five times smaller than micelles formed in the corresponding samples in D2O.

  • 2084.
    Bergström, M
    YKI – Ytkemiska institutet.
    Derivation of expressions for the spontaneous curvature, mean and Gaussian bending constants of thermodynamically open surfactant monolayers and bilayers2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 118, p. 1440-1452Article in journal (Refereed)
    Abstract [en]

    We have derived expressions for the spontaneous curvature H0, the mean and Gaussian bending constants, kc and c, respectively, for a surfactant film of finite thickness that is open in a thermodynamic sense. Geometrical packing constraints are taken into account and give rise to explicit large and important contributions to kc c, and kcH0. From its contribution to the latter quantity we may deduce that surfactant aggregates (micelles, vesicles, microemulsion droplets) are expected to dramatically increase their size with increasing surfactant tail length. Moreover, the coupling between free energy contributions related to surfactant head group and tail with geometrical packing constraints give rise to dominant terms on the form 2 pH0, where p is the thickness of a planar film, in the expressions for kc In the case of repulsive head group effects that favor a large spontaneous curvature, such as electrostatics, these terms raise kc and thus increase the rigidity of the film. Due to the constraint of constant free monomer chemical potentials, the composition of the film becomes a function of curvature. As a result, the ability of a surfactant film to have different surfactant compositions in differently curved parts (e.g., inner and outer layer of a vesicle, central parts and end caps of rod or threadlike micelles, etc.) may considerably reduce kc, whereas c and kcH0 are mainly unaffected by mixing. The magnitude of the reduction of kc of a binary surfactant film increases with increasing asymmetry between the two surfactants with respect to charge number, head group size, and tail volume

  • 2085.
    Bergström, M
    YKI – Ytkemiska institutet.
    Molecular interpretation of the mean bending constant for a thermodynamically open vesicle bilayer2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, p. 7675-7686Article in journal (Refereed)
    Abstract [en]

    Expressions for the various molecular contributions to the mean bending constant kc of a thermodynamically open vesicle bilayer have been derived, from which kc may be calculated from an appropriate molecular-thermodynamic model as a function of the structure of the surfactants making up the aggregates as well as the solution state. It is demonstrated that kc determines the shape of a vesicle bilayer insofar as spherical vesicles form when kc is large and positive whereas nonspherical vesicles predominate at values of kc close to or below zero. It is found that contributions due to electrostatics and residual headgroup effects, which are present for one-component as well as mixed aggregates, mainly give rise to a positive value of kc whereas geometrical packing constraints are less important. However, the mixing of two or more surfactants can significantly reduce kc to values where nonspherical vesicles may begin to form. The magnitude of the reduction of kc due to mixing increases with increasing asymmetry with respect to headgroup cross-section area, charge number, and hydrocarbon tail volume between two surfactants in a binary surfactant mixture. The asymmetry is most pronounced for a binary mixture where the surfactant that carries the charge has the larger headgroup and the smaller tail. The reduction of kc due to mixing is, however, expected to be less than the corresponding effect for the bilayer bending constant of a spherical vesicle as a result of an additional positive contribution in the expression for the compositional contribution to kc

  • 2086.
    Bergström, M
    YKI – Ytkemiska institutet.
    Synergistic effects in mixtures of an anionic and a cationic surfactant2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, p. 993-998Article in journal (Refereed)
    Abstract [en]

    Synergistic effects in mixtures of an anionic and a cationic surfactant have been theoretically investigated. We derive an explicit expression for the critical micelle concentration (cmc) as a function of the aggregate composition from the Poisson-Boltzmann mean field theory and, thus, demonstrate that the conspicuously large synergistic effects that have been experimentally observed can be rationalized without the need of invoking any specific interactions between the surfactant headgroups. The simple relation = -4el/kT is derived, i.e., the "interaction parameter" is directly related to the electrostatic free energy contribution el for the pure surfactant, implying, among other things, that the magnitude of decreases with increasing cmc for the pure surfactant in agreement with experimental observations. We furthermore demonstrate that the aggregate composition is close to equimolar composition (x1 = 0.5) at cmc in almost the entire regime of overall surfactant compositions and that the free monomer concentration of the surfactant in excess is generally much larger than the corresponding quantity for the surfactant in deficit.

  • 2087.
    Bergström, M
    YKI – Ytkemiska institutet.
    Thermodynamics of anisotropic surfactant micelles. I. The influence of the curvature free energy on the micellar size and shape2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, p. 5559-5568Article in journal (Refereed)
    Abstract [en]

    A novel theory for the structural behavior of surfactant micelles is expounded. The micelles are considered to be generally shaped as triaxial tablets with distinct thickness width and length, respectively, and may become spherical, spherocylindrical or disk-shaped in the special cases where two or more of the dimensions are equal. It is demonstrated that the average width and length of a tablet-shaped micelle with a fixed thickness is mainly determined by two constants, k1 and k2, related to the first and second order correction in curvature of the micellar end caps. The size of the micelles is found to be mainly determined by k1, whereas k2 influences the shape, i.e., the length-to-width ratio, of the micelles so that the micellar size increases with increasing k1 and the length-to-width ratio decreases with increasing k2. Hence, large positive values of k2 promote the formation of tablets rather than very long spherocylinders. An additional parameter related to the curvature of the straight cylindrical rims may influence the structure of the tablet-shaped micelles insofar k2 is close to or below zero.

  • 2088.
    Bergström, M
    YKI – Ytkemiska institutet.
    Thermodynamics of anisotropic surfactant micelles. II. A molecular interpretation of the micellar curvature free energy2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, p. 5569-5579Article in journal (Refereed)
    Abstract [en]

    Explicit expressions have been derived for the two curvature constants k1 and k2 that mainly influence the size and shape, respectively, of generally shaped micelles (triaxial tablets with a thickness

  • 2089.
    Bergström, M
    YKI – Ytkemiska institutet.
    Thermodynamics of surfactant micelles and vesicles2001In: Handbook of Surfaces and Interfaces of Materials: Biomolecules, Biointerfaces and Applications / [ed] Hari Singh Nalwa, Academic Press, 2001, p. 233-264Chapter in book (Refereed)
  • 2090.
    Bergström, M
    YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Thermodynamics of unilamellar vesicles: Influence of mixing on the curvature free energy of a vesicle bilayer2001In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 240, p. 294-306Article in journal (Refereed)
    Abstract [en]

    Endothelial cell layers from umbilical cords were grown on methylated silica surfaces. Fluorescence microscopy showed this layer to be confluent and to consist of living cells. Initial ellipsometry measurements were performed to illustrate both the stability of the model surface in ellipsometry measurements and the Ca2+-dependent binding of lipoproteins at the cell-based substrate. The present substrate holds promise as a model substrate for in vitro investigations of lipoprotein deposition at the endothelium surface under close to in vivo conditions.

  • 2091.
    Bergström, M
    SP – Sveriges Provnings- och Forskningsinstitut.
    Update of Nordtest methods for testing of packagings1995Report (Refereed)
  • 2092.
    Bergström, M
    et al.
    YKI – Ytkemiska institutet.
    Eriksson, JC
    YKI – Ytkemiska institutet.
    A theoretical analysis of synergistic effects in mixed surfactant systems2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 7173-7181Article in journal (Refereed)
    Abstract [en]

    Synergistic effects in mixed binary surfactant systems have been investigated by analyzing the main contributions to the free energy of forming a mixed surfactant aggregate. We show that a nonlinear behavior of the critical micelle concentration (cmc) with respect to the surfactant composition of the aggregates is determined by a nonlinear behavior of the free energy per aggregated surfactant. It appears that synergistic effects are due mainly to entropic free energy contributions related with the surfactant headgroups. For a mixture of a monovalent ionic and a nonionic surfactant in the absence of added salt we obtain, entirely because of electrostatic reasons, a negative deviation from ideal behavior of the cmc vs the aggregate composition corresponding to an interaction parameter -1, whereas values on the order of -5 or even less can arise for mixtures of two ionic surfactants with the same charge number but with different hydrocarbon moieties. Moreover, we introduce a novel expression for the free energy of mixing aggregated surfactant headgroups with surrounding solvent molecules. Accordingly, synergistic effects arise as a result of different headgroup cross-section areas in mixtures of two nonionic surfactants with rigid headgroups. These effects are found to be rather small, with 0 > > -1, when the difference in headgroup size is modest but can become more significant when the size difference is larger. In mixtures of an ionic and a nonionic surfactant with different headgroup cross-section areas the two contributions to synergistic effects always enhance one another and, hence, values below -1 are obtained. Generally, the synergistic effects tend to increase with increasing asymmetry between the two surfactants.

  • 2093.
    Bergström, M
    et al.
    YKI – Ytkemiska institutet.
    Eriksson, JC
    YKI – Ytkemiska institutet.
    Synergistic effects in binary surfactant mixtures2004In: Progress in Colloid and Polymer Science, ISSN 0340-255X, E-ISSN 1437-8027, Vol. 123, p. 16-22Article in journal (Refereed)
    Abstract [en]

    By considering the main contributions to the micellar free energy we have analysed the synergistic effect often seen on the CMC of a binary surfactant mixture. The synergistic effects are due mainly to the entropic free energy contributions related with the surfactant head groups. Several cases have been treated: (i) For a mixture of a monovalent ionic and a non-ionic surfactant in the absence of added salt we obtain, entirely because of electrostatic reasons, a negative deviation from the ideal behaviour corresponding to an interaction parameter β≈-1. Upon adding an inert salt we found that the magnitude of the synergistic effect first increases, reaches a maximum and eventually decreases. (ii) For mixtures of two ionic surfactants with the same charge number but with different hydrocarbon moieties β-values as low as -10 may arise. (iii) For mixtures of an anionic and a cationic surfactant enormous effects are anticipated yielding β≤-20 depending on the CMCs of respective pure surfactant. (iv) Synergistic effects due to different cross-section areas of the head groups are found to be rather small, with 0 > β > -1, provided the difference in head group size is modest but can become more significant when the size difference is larger.

  • 2094.
    Bergström, M
    et al.
    YKI – Ytkemiska institutet.
    Jonsson, P
    YKI – Ytkemiska institutet.
    Persson, M
    YKI – Ytkemiska institutet.
    Eriksson, JC
    YKI – Ytkemiska institutet.
    A model independent evaluation of experimental data, and comparison with theory, of synergistic effects in mixtures of an ionic and a nonionic surfactant2003In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, p. 10719-10725Article in journal (Refereed)
    Abstract [en]

    Critical micelle concentrations for mixtures of an anionic (sodium dodecyl sulfate) and a nonionic (decyl β-glucoside) surfactant was obtained from surface tension measurements at different concentrations of added NaCl. The observed synergistic effects were analyzed by means of introducing a novel model-independent synergy parameter. The model-independent evaluation has enabled the comparison of experimental results with a theoretical model based on the Poisson-Boltzmann (PB) mean field theory for spherical, cylindrical, and planar geometries, respectively. We found that best agreement with experimental data was obtained for largely curved structures (spherical and cylindrical micelles) at all [NaCl], which is consistent with the fact that rather small micelles, as a rule, form at the critical micelle concentration. Moreover, the PB theory was found to better describe synergistic behavior of the experimental data than the more conventional regular mixture theory, in particular at low electrolyte concentrations. The magnitude of the observed synergistic effects was found to increase as a small amount of NaCl was added and reach a maximum at [NaCl] = 10 mM, in agreement with the PB theory. As expected, synergism was observed to decrease in magnitude upon further addition of NaCl.

  • 2095. Bergström, M
    et al.
    Kjellin, URM
    Claesson, PM
    YKI – Ytkemiska institutet.
    Grillo, I
    Small-angle neutron scattering study of mixtures of cationic polyelectrolyte and anionic surfactant: Effect of polyelectrolyte charge density Polyelectrolyte and Anionic Surfactant: Effect of Polyelectrolyte Charge2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, p. 1874-1881Article in journal (Refereed)
    Abstract [en]

    We have studied mixtures of an anionic surfactant (deuterated sodium dodecyl sulfate, SDS-d) and cationic polyelectrolytes with different charge densities (10%, 30%, 60%, and 100%) using small-angle neutron scattering (SANS). Near compositions corresponding to charge neutralization, the solutions phase separate into a complex phase (precipitate) consisting of, in the cases of 30%, 60%, and 100% charge density, a two-dimensional (2D) hexagonal lattice of close-packed cylindrical micelles and a clear liquid. When either polyelectrolyte with charge density less than 100% or SDS-d is present in sufficient excess, the solution becomes clear and isotropic, and from the scattering data we may conclude that prolate or rod-shaped micelles are present. The micelles are seen to grow in length with increasing SDS-d concentration and polyelectrolyte charge density from about 80 Å to 550 Å, whereas the cross-sectional radius is 15 Å and approximately constant. The number of micelles per polyelectrolyte chain is found to be slightly larger than unity (1-6). In some of the (turbid) samples rod-shaped micelles are found to coexist with larger polyelectrolyte-surfactant complexes. Solutions consisting of 10% charged polyelectrolyte and SDS-d are very viscous and gellike, and the complex phase is much less defined with a much larger distance between adjacent aggregates in the complex phase.

  • 2096.
    Bergström, M
    et al.
    YKI – Ytkemiska institutet.
    Kjellin, URM
    Claesson, PM
    YKI – Ytkemiska institutet.
    Pedersen, JS
    Nielsen, MM
    A small-angle x-ray scattering study of complexes formed in mixtures of a cationic polyelectrolyte and an anionic surfactant2002In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 106, p. 11412-11419Article in journal (Refereed)
    Abstract [en]

    The internal structure of the solid phase formed in mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and a range of oppositely charged polyelectrolytes with different side chains and charge density has been investigated using small-angle X-ray scattering. Polyelectrolytes with short side chains [3-(2-methylpropionamido)propyl]trimethylammonium chloride, MAPTAC, and poly{[(2-propionyloxy)ethyl]trimethylammonium chloride}, PCMA) form a 2-dimensional hexagonal structure with SDS, whereas a polyelectrolyte without side chains (poly(vinlyamine), PVAm) forms a lamellar structure. The hexagonal structure of MAPTAC is retained either when a neutral monomer (acrylamide, AM) is included in the polymer backbone to reduce the charge density or when a nonionic surfactant is admixed to the SDS/polyelctrolyte complex. The unit cell length of AM-MAPTAC increases with decreasing charge density from a = 47.7 Å (MAPTAC, 100% charge density) to 58.5 Å (AM-MAPTAC, 30% charge density). The unit cell length in the lamellar SDS/PVAm complex (a = 36.1 Å) is significantly smaller than for the different hexagonal structures. It is conjectured that the cylinders in the hexagonal structure and the bilayers in the lamellar structure are based on self-assembled surfactant aggregates with the polyelectrolyte mainly located in the aqueous region adjacent to the charged surfactant headgroups

  • 2097.
    Bergström, M
    et al.
    YKI – Ytkemiska institutet.
    Pedersen, JS
    A small-angle neutron scattering study of surfactant aggregates formed in aqueous mixtures of sodium dodecyl sulfate and didodecyldimethylammonium bromide2000In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 104, p. 4155-4163Article in journal (Refereed)
    Abstract [en]

    The structure of aggregates formed in aqueous mixtures of a single-chain anionic surfactant, sodium dodecyl sulfate (SDS), and a double-chain cationic surfactant, didodecyldimethylammonium bromide (DDAB), has been investigated at 38° C using small-angle neutron scattering (SANS). Several overall surfactant concentrations [SDS] + [DDAB] between 0.1 and 5 wt % were measured at the two SDS-rich compositions [SDS]:[DDAB] = 90:10 and 95:5. Samples with a concentration above about [SDS] + [DDAB] = 1 wt % at [SDS]:[DDAB] = 95:5 contained only somewhat elongated tablet-shaped micelles (triaxial ellipsoids) with typical values of the half-axes a (related to the thickness) = 14 Å, b (related to the width) = 23 Å, and c (related to the length) = 27 Å. When a sample at [SDS]:[DDAB] = 95:5 is diluted below about [SDS] + [DDAB] = 1 wt %, an increasing amount of small unilamellar vesicles forms, and in the samples below about 0.2 wt %, only vesicles are observed. The average radius of the vesicles increases from about 90 Å at 0.3 wt % to 110 Å at 0.1 wt %. The transition from micelles to vesicles with decreasing surfactant concentration was also observed in the samples at [SDS]:[DDAB] = 90:10 in which, however, an additional amount of bilayer sheets was seen to be always present. Compared with the micelles at [SDS]:[DDAB] = 95:5, the micelles formed at [SDS]:[DDAB] = 90:10 were considerably longer (c ≈40 Å), but with similar cross section dimensions, and the vesicles formed were seen to be somewhat larger than the corresponding aggregates at 95:5. The relative standard deviation σR/ of the (number-weighted) vesicle size distributions was in the range 0.2 < σR/ < 0.3.

  • 2098.
    Bergström, Magnus
    YKI – Ytkemiska institutet.
    Size and shape analysis of micellar systems2002In: Encyclopedia of Surface and Colloid Science / [ed] Hubbard A and Somasundaran P, Marcel Dekker, 2002, p. 4684-4699Chapter in book (Refereed)
  • 2099.
    Bergström, Sven G
    CBI - Cement- och betonginstitutet.
    An experimental study of the relation between the properties of fresh and hardened concrete1953Report (Refereed)
  • 2100.
    Bergström, Sven G
    CBI - Cement- och betonginstitutet.
    Forskning och utveckling inom betongteknologin1977Report (Refereed)
39404142434445 2051 - 2100 of 20511
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