| 1. |
- Bergeron, V., et al.
(författare)
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Structural forces reflecting polyelectrolyte organization from bulk solutions and within surface complexes
- 2002
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 96:03-jan, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between two macroscopic surfaces approaching one another underlies many of the phenomena observed in Colloid and Interface science. In Russia this gave rise to the branch of colloid science now referred to as Surface Forces. Important discoveries, such as the molecular organization of solvent molecules at an interface, have been unveiled by surface force measurements. More recently, forces and structures at macromolecular length scales have been uncovered. In particular, oscillatory force profiles have been detected from aqueous solutions containing polyelectrolytes. The force-structure relationship can reflect organization in the bulk solution or the internal structure of the adsorbed layer. Using a range of surface force techniques, combined with X-ray and neutron scattering results, we review the main features of these fascinating systems and provide an overview of how they relate to other systems such as micellar solutions, polymer-surfactant complexes and simple solvents.
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| 2. |
- Christenson, H. K., et al.
(författare)
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Direct measurements of the force between hydrophobic surfaces in water
- 2001
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 91:3, s. 391-436
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Forskningsöversikt (refereegranskat)abstract
- Direct measurements of the force between hydrophobic surfaces across aqueous solutions are reviewed. The results are presented according to the method of preparation of the hydrophobic surfaces. No single model appears to fit all published results, and an attempt is made to classify the measured interactions in three different categories. The large variation of the measured interaction, often within each class, depending on the type of hydrophobic surface is emphasized. (I) Stable hydrophobic surfaces show only a comparatively short-range interaction, although little quantitative data on this attraction have been published. (II) Many results showing very long-range attractive forces are most likely due to the presence of sub-microscopic bubbles on the hydrophobic surfaces. Such an interaction is typically measured between silica surfaces made hydrophobic by silylation. Between self-assembled thiol layers on gold surfaces very short-range attractive forces are possibly due to the presence or nucleation of bubbles. The reason for the apparent stability of these bubbles is not clear and warrants further investigation. (III) Results obtained with LB films of surfactants or lipids on mica appear to give rise to a different type of force that fits neither of these two categories. This force is an exponentially decaying attraction, often of considerable range. The force turns more attractive at smaller separations, and may at short range be similar to the interaction measured between stable hydrophobic surfaces. An apparently similar, exponential attraction is also found between mica surfaces bearing surfactants adsorbed from cyclohexane, between silylated, plasma-treated mica surfaces and between both mica and silica surfaces with surfactants adsorbed in situ. This type of force also occurs between some surfaces of relatively low hydrophobicity as well as between one such hydrophobic surface and a hydrophilic surface. No convincing model can explain this third type of interaction for all systems in which it has been observed. This review of work to date points to the importance of the morphology and structure of the hydrophobic surface, and how it may change during the interaction of two surfaces.
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| 3. |
- Claesson, Per M., et al.
(författare)
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Polyelectrolytes as adhesion modifiers
- 2003
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 104, s. 53-74
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Tidskriftsartikel (refereegranskat)abstract
- Adsorbed layers of polyelectrolytes have been studied with atomic force microscopy (AFM) and the interferometric surface force apparatus (SFA). Particular emphasis was put on determining the effect of the polyelectrolyte charge density on surface topography, and the effect of the polyelectrolyte coating on the adhesive properties. The AFM was employed to image individual polymer chains at low adsorption densities and to characterize the layer topography and coverage at higher adsorption densities. The adhesive properties between two polyelectrolyte-coated surfaces in air were determined as a function of the number of contacts made at any given spot. The data provide evidence for formation of electrostatic bridges, particularly when highly charged polyelectrolytes are used. Further, material transport between the surfaces is observed when the polyelectrolyte is either highly charged or have a very low charge density. For intermediate charge densities we could not observe any indication of material transfer. The adhesion between one polyelectrolyte-coated surface and one bare surface was initially higher than that between two polyelectrolyte-coated surfaces. However, due to material transfer between the two surfaces the adhesion decreased significantly with the number of times that the surfaces were driven into contact. For the polyelectrolytes of the lowest charge density the results suggest that entanglement effects contribute to the adhesive interaction. The modification of the adhesion by polyelectrolytes in practical systems such as in the case of dry-strength additives to improve paper resistance is also considered.
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| 4. |
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| 5. |
- Sharma, P.K., et al.
(författare)
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Analysis of different approaches for evaluation of surface energy of microbial cells by contact angle goniometry
- 2002
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 98:3, s. 341-463
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Tidskriftsartikel (refereegranskat)abstract
- Microbial adhesion on solid substrate is important in various fields of science. Mineral–microbe interactions alter the surface chemistry of the minerals and the adhesion of the bacterial cells to mineral surface is a prerequisite in several biobeneficiation processes. Apart from the surface charge and hydrophobic or hydrophilic character of the bacterial cells, the surface energy is a very important parameter influencing their adhesion on solid surfaces. There were many thermodynamic approaches in the literature to evaluate the cells surface energy. Although contact angle measurements with different liquids with known surface tension forms the basis in the calculation of the value of surface energy of solids, the results are different depending on the approach followed. In the present study, the surface energy of 140 bacterial and seven yeast cell surfaces has been studied following Fowkes, Equation of state, Geometric mean and Lifshitz–van der Waals acid–base (LW–AB) approaches. Two independent issues were addressed separately in our analysis. At first, the surface energy and the different components of the surface energy for microbial cells surface are examined. Secondly, the different approaches are evaluated for their internal consistency, similarities and dissimilarities. The Lifshitz–van der Waals component of surface energy for most of the microbial cells is realised to be approximately 40 mJ/m2±10%. Equation of state and Geometric mean approaches do not possess any internal consistency and yield different results. The internal consistency of the LW–AB approach could be checked only by varying the apolar liquid and it evaluates coherent surface energy parameters by doing so. The electron-donor surface energy component remains exactly the same with the change of apolar liquid. This parameter could differentiate between the Gram-positive and Gram-negative bacterial cells. Gram-negative bacterial cells having higher electron-donor parameter had lower nitrogen, oxygen and phosphorous content on their cell surfaces. Among the four approaches, LW–AB was found to give the most consistent results. This approach provides more detailed information about the microbial cell surface and the electron–donor parameter differentiates different type of cell surfaces.
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| 6. |
- Stalgren, J. J. R., et al.
(författare)
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Adsorption of liposomes and emulsions studied with a quartz crystal microbalance
- 2001
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 89, s. 383-394
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption from phospholipid liposome solutions (1.2%) and phospholipid stabilized oil-in-water emulsions (20% purified soybean oil) with the same phospholipid liposome concentration, has been followed by means of a quartz crystal microbalance allowing the simultaneous determination of changes in resonance frequency and energy dissipation. Both the fundamental resonance frequency and the third overtone were used for following the interfacial processes. The adsorption from the liposome solution resulted in formation of a phospholipid bilayer with an additional and incomplete outer layer of liposomes. The outer layer was removed by dilution leaving a bilayer of phospholipids on the surface. The adsorption process observed from the concentrated emulsion solution was considerably more complex. A slow spreading process that also resulted in some expulsion of material from the interface followed the rapid initial adsorption of emulsion droplets. After rinsing with water a phospholipid bilayer was retained on the surface.
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| 7. |
- Antunes, Filipe E., et al.
(författare)
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Polymer-vesicle association
- 2009
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 1873-3727 .- 0001-8686. ; 147-48, s. 18-35
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Forskningsöversikt (refereegranskat)abstract
- Mixed polymer-surfactant systems have been intensively investigated in the last two decades, with the main focus on surfactant micelles as the surfactant aggregate in interaction. The main types of phase behavior, driving forces and structural/rheological effects at stake are now fairly well understood. Polymer-vesicle systems, on the other hand, have received comparatively less attention from a physico-chemical perspective. In this review, our main goal has been to bridge this gap, taking a broad approach to cover a field that is in clear expansion, in view of its multiple implications for colloid and biological sciences and in applied areas. We start by a general background on amphiphile self-assembly and phase separation phenomena in mixed polymer-surfactant solutions. We then address vesicle formation, properties and stability not only in classic lipids, but also in various other surfactant systems, among which catanionic vesicles are highlighted. Traditionally. lipid and surfactant vesicles have been studied separately, with little cross-information and comparison, giving duplication of physico-chemical interpretations. This situation has changed in more recent times. We then proceed to cover more in-depth the work done on different aspects of the associative behavior between vesicles (of different composition and type of stability) and different types of polymers, including polysaccharides. proteins and DNA. Thus. phase behavior features. effects of vesicle structure and stability, and the forces/mechanisms of vesicle-macromolecule interaction are addressed. Such association may generate gels with interesting theological properties and high potential for applications. Finally, special focus is also given to DNA, a high charge polymer. and its interactions with surfactants, and vesicles. in particular, in the context of gene transfection studies. (C) 2008 Elsevier B.V. All rights reserved
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| 8. |
- Bain, C. D., et al.
(författare)
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Complexes of surfactants with oppositely charged polymers at surfaces and in bulk
- 2010
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 155:1-2, s. 32-49
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Tidskriftsartikel (refereegranskat)abstract
- Addition of surfactants to aqueous solutions of polyelectrolytes carrying an opposite charge causes the spontaneous formation of complexes in the bulk phase in certain concentration ranges. Under some conditions, compact monodisperse multichain complexes are obtained in the bulk. The size of these complexes depends on the mixing procedure and it can be varied in a controlled way from nanometers up to micrometers. The complexes exhibit microstructures analoguous to those of the precipitates formed at higher concentrations. In other cases, however, the bulk complexes are large, soft and polydisperse. In most cases, the dispersions are only kinetically stable and exhibit pronounced non-equilibrium features. Association at air-water interfaces readily occurs, even at very small concentrations. When the surfactant concentration is small, the surface complexes are usually made of a surfactant monolayer to which the polymer binds and adsorbs in a flat-like configuration. However, under some conditions, thicker layers can be found, with bulk complexes sticking to the surface. The association at solid-water interfaces is more complex and depends on the specific interactions between surfactants, polymers and the surface. However, the behaviour can be understood if distinctions between hydrophilic surfaces and hydrophobic surfaces are made. Note that the behaviour at air-water interfaces is closer to that of hydrophobic than that of hydrophilic solid surfaces. The relation between bulk and surface complexation will be discussed in this review. The emphasis will be given to the results obtained by the teams of the EC-funded Marie Curie RTN "SOCON".
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| 9. |
- Balogh, Joakim
(författare)
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Determining scaling in known phase diagrams of nonionic microemulsions to aid constructing unknown.
- 2010
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 1873-3727 .- 0001-8686. ; 159:1, s. 22-31
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Tidskriftsartikel (refereegranskat)abstract
- Microemulsions based on nonionic surfactants of the ethylene oxide alkyl ether type C(m)E(n), have been studied thoroughly for around 30years. Thanks to the considerable amount of published data available on these systems, it is possible to observe trends to make predictions of phase diagrams not yet determined. Strey and Kahlweit, and subsequently Sottmann and Strey, with coworkers have studied and published phase diagrams for systems with a fixed ratio of oil to water, varying the surfactant, the so-called Kahlweit fish-cut diagrams. Some properties of the phase diagrams can be scaled to become general and not system dependent. Here are shown two examples of scaling data from phase diagrams and the use of trends to determine phase diagrams, both inside and outside a dataset. The trends of microemulsions with fixed ratio of surfactant to oil, the so-called Lund-cut diagrams, are also investigated. The trends are used to determine a new phase diagram and this is compared with previously unpublished experimental data on C(12)E(5)-Octadecane-Water system. The scalings and trends make it possible to get good estimations of many of the important properties of the phase diagrams, both temperatures and surfactant concentrations of interest, by investigating one sample in the 3-phase region of the balanced fish-cut diagram.
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| 10. |
- Bergström, L
(författare)
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Hamaker constants of inorganic materials
- 1997
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 70, s. 125-169
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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