Solvents polymeric surfactant adsorption

The position of point A in the curve shown in Fig. 1.7 is characteristic for a sufficient purity of the surfactant and solvent. The point is located at a definite surface tension and concentration (CMC). As a rule, a minimum in the y(c) or y(log c) plot is evidence of traces of highly surface-active impurities which affect the results [147]. In chapters 2 to 4 the effect of lateral molecular interaction with increasing alkyl chain length, the effects of changes in orientation and conformation, essentially shown by polymeric surfactants such as proteins, may also lead to significant changes in the adsorption behaviour. 

This chapter described the basis principles involved in stabilization of dispersions by polymeric surfactants. The first part described polymeric surfactants and their solution properties. The second part described the adsorption of polymeric surfactants and their conformation at the interface. The methods that can be applied to determine the adsorption and conformation of polymeric surfactants were briefly described. The third part dealt with the stabilization mechanism produced using polymeric surfactants. Two main repulsive forces were considered. The first arises from the unfavorable mixing of the chains on close approach of the particles or droplets, when these chains are in good solvent conditions. This is referred to as mixing or osmotic repulsion. The second force of repulsions... 

In view of such applications, the adsorption of a grafted (rake-type) polymeric siloxane surfactant containing 48% PDMS, 39% PEO, and 13% PPO on carbon black particles dispersed in mixtures of water with polar organic solvents has been investigated [58]. The adsorption was foimd to obey the Langmuir isotherm below the critical micelle concentration and a sharp increase in the adsorbed amount was observed at higher surfactant concentrations. DLS and SANS data indicate that the structure of the adsorbed layer is similar to that of micelles. 

A cross-linked structure has been obtained by in situ polymerization, producing a stable substrate to surfactant solutions, organic solvents, and to transfer across the air/water interface, yet retaining the resistance to the nonspecific protein adsorption characteristic of a fluid phosphatidylcholine bilayer. 

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