Adsorbed layer, activity stability

A polysaccharide can be added as a component in a protein system to produce a protein-polysaccharide composite structure. Tolstoguzov (2003) reviewed the main function of protein and polysaccharide in protein-polysaccharide food formulation. Generally, polysaccharides have less surface activity in comparison to proteins. This inferiority is related to their low flexibility and monotonic repetition of the monomer units in the backbone. The low surface activity of polysaccharides results in their inability to form a primary adsorbed layer in the system. The nature of interactions between polysaccharides and adsorbed proteins, as well as their influence on colloid stability, can either stabilize or destabilize the emulsions. Attractive protein-polysaccharide interactions can enhance the emulsion stability by forming a thicker and stronger steric-stabilizing layer. In contrast, the attractive interactions... 

Foam Stability at Low Surfactant Concentrations Role of Surface Rheological Properties. At surfactant concentrations below or around the CMC, the adsorption of the surface-active molecules on the film surfaces and the properties of the adsorbed layers control the drainage and stability of the film and the foam. 

It is therdbre possible to predict, with some confidence, the stability of a dispersion from readily obtainable parameters, and this has been done for hydrocarbon media for a range of particle size and surface potential. The validity of the DLVO theory has been demonstrated both by qualitative and by rigorous experimental tests on systems in which there is no significant influence of the interaction of adsorbed layers of surface-active material, i.e. only the charge mechanism is operative. However the origin of the charge on the particles is still subject to debate. 

Micropipet technique can also be used for studies of die adsorbed layer formed on emulsion droplets. Many natural components of crude oil are surface active and will tend to adsorb on the hydrocarbon-water interface (20). Surface excess of the adsorbed material can then be calculated from the Gibbs equation. In our case, we will use the concentration of bitumen in the solvent, since we do not know what is the chemical(s) responsible for droplet stabilization and what its concentration is. We will use the micropipet technique diseussed above, to measure true IFT at emulsion drop surfaees. 

In systems of dispersed particles containing adsorbed layers of surface-active substances, the effective Hamaker constant between the particle and the medium may be radically altered. If the Hamaker constant of the solvation sheath is close to that of the dispersion medium, the sheath simply acts as a mechanical barrier preventing the close approach of the dispersed particles in the range where attractive forces become strong. This layer would then contribute to stability. 

The only way significant amounts of immiscible fluids can be mixed together is if the interfacial layer surrounding the dispersed droplets is occupied by an adsorbed layer of molecules that keep the droplets from coalescing. Figure 1.1 shows the importance of the interfacial layer in emulsion systems for the two main classes of surface-active molecules, surfactants and proteins, that stabilize them. Low molecular weight surfactants, lipids, and emulsifiers self-assemble at interfaces with the appropriate part of the molecule associating with the appropriate hydrophilic or hydrophobic phases. Proteins, on the other hand. 

Suspensions of oil in water (32), such as lanolin in wool (qv) scouring effluents, are stabilized with emulsifiers to prevent the oil phase from adsorbing onto the membrane. Polymer latices and electrophoretic paint dispersions are stabilized using surface-active agents to reduce particle agglomeration in the gel-polarization layer. 

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