Chain-solvent interactions, polymeric surfactant

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. 

It is clear from Equation 14.18 that when the Flory-Huggins interaction parameter, % is <0.5, that is, the chains are in good solvent conditions, is positive, and the interaction is repulsive and increases very rapidly with decreasing h, when the latter is lower than 28. This explains why polymeric surfactants such as Hypermer CG6 (a graft copolymer of polymethylmethacrylate backbone and PEO side chains, produced by ICl) are ideal for stabilizing dispersions in aqueous media. For stabilization of dispersions in nonaqueous media, such as w/o emulsions, the stabilizing chains have to be soluble in the oil phase (normally a hydrocarbon). In this case, polyhydroxystearic acid (PHS) chains are ideal. A polymeric surfactant such as Aralcel P135 (an ABA block copolymer of PHS-PEO-PHS produced by ICl) is an ideal w/o emulsifier. 

One of the recent topics in studies of dynamic light scattering is finding the slow mode for polymeric systems. First observation of the slow mode was reported on the semidilute solutions of polystyrene in theta solvent by Adam and Delsanti [1]. Since then, the slow mode has been observed in several solutions in theta or poor solvents where polymer chains tend to associate with each other weakly [2-5]. Besides them, in recent years, the slow relaxation mode was also observed in the thread-like micellar system formed by the cationic surfactant in aqueous solutions [6]. If weak interaction between chains... 

In Equations 4.7 and 4.8, a is a typical monomer size and Y is a surface tension in which are lumped all pair interactions. As noted by the authors, Tj depends on the lengths (polymerization degrees) of the soluble and insoluble blocks for the starlike micelles but does not depend on the length of the soluble block for micelles with a thin corona. The comparison of the exponential factors in Equation 4.5 and in Equations 4.7 and 4.8 shows that a is the equivalent of and that the variation of k with the chain length of the insoluble block (m or Nb) is slower for block copolymers than for surfactants. The Nb factor in Equations 4.7 and 4.8 reflects the assumed collapsed conformation of the insoluble block of the copolymer. The interaction of the insoluble block with the solvent and the soluble block occurs at the surface of the spheroid formed by the collapsed insoluble block in the unimer state. It is thus proportional to the surface of this block that scales as Nb . 

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