| 1. |
- Bergeron, V., et al.
(författare)
-
Structural forces reflecting polyelectrolyte organization from bulk solutions and within surface complexes
- 2002
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 96:03-jan, s. 1-20
-
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.
|
|
| 2. |
- Christenson, H. K., et al.
(författare)
-
Direct measurements of the force between hydrophobic surfaces in water
- 2001
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 91:3, s. 391-436
-
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.
|
|
| 3. |
- Claesson, Per M., et al.
(författare)
-
Polyelectrolytes as adhesion modifiers
- 2003
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 104, s. 53-74
-
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.
|
|
| 4. |
|
|
| 5. |
- Sharma, P.K., et al.
(författare)
-
Analysis of different approaches for evaluation of surface energy of microbial cells by contact angle goniometry
- 2002
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 98:3, s. 341-463
-
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.
|
|
| 6. |
- Stalgren, J. J. R., et al.
(författare)
-
Adsorption of liposomes and emulsions studied with a quartz crystal microbalance
- 2001
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 89, s. 383-394
-
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.
|
|
| 7. |
- Folmer, BM
(författare)
-
Sterol surfactants: from synthesis to applications
- 2003
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 103, s. 99-119
-
Tidskriftsartikel (refereegranskat)abstract
- An overview is given of sterol surfactants, including raw material aspects, classification and synthesis routes, physico-chemical behaviour and applications in pharmaceuticals and cosmetics.
|
|
| 8. |
|
|
| 9. |
- Kizling, J, et al.
(författare)
-
On the formation of concentrated stable w/o emulsions
- 2001
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 89-90, s. 395-399
-
Tidskriftsartikel (refereegranskat)abstract
- The conditions for the formation of concentrated w/o emulsions based on Aerosol OT and aliphatic hydrocarbons were studied. It was found that high stability is obtained if the attraction between the emulsion droplets is kept to a minimum. This is achieved by matching the refractive index of the dispersed phase and the organic phase. Furthermore, it is shown that the mere presence of salt does not render any stability. Hence, the speculated mechanism that salt stabilises against Ostwald ripening does not hold for these emulsions.
|
|
| 10. |
- Liljekvist, P, et al.
(författare)
-
The surface pressure effect of pentaoxyethylene and maltoside surfactant head groups
- 2001
-
Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 89-90, s. 293-302
-
Tidskriftsartikel (refereegranskat)abstract
- From experimental surface tension data for water solutions of dodecyl-b-maltoside, C12M, and dodecyl penta (ethylene oxide), C12EO5, in the range below the CMC, the corresponding head group surface pressure functions vs. packing density have been derived. These functions are compared with theoretical expressions based on some different models of the mixed head group/water layer. Tentatively, we conclude that the two-dimensional hard fluid approach furnishes a convenient starting-point in order to account for the observed surface pressures of both the maltoside and EO head groups.
|
|
