Interactions between cationic mixed micelles and poly(vinyl pyrrolidone)

The conductances of trimethyltetradecylammonium bromide (TTAB) + trimethylhexa decylammonium bromide (HTAB) and TTAB + trimethyldodecylammonium bromide (DTAB) mixtures over the entire mole fraction range were measured in aqueous poly(vinyl pyrrolidone) (PVP) containing 1-10 wt% PVP at 30 degrees C. Each conductivity (k) curve for the TTAB + HTAB mixtures showed two breaks corresponding to two aggregation processes over the whole mole fraction range, except in the case of pure TTAB, where a single break corresponding to the conventional critical micelle concentration (cmc) was observed. In the case of TTAB + DTAB mixtures, each k curve at a particular mole fraction of TTAB showed only one break, which was quite close to a similar one in pure water. In TTAB + HTAB mixtures, the first break is called the critical aggregation concentration. It is dose to the conventional cmc and is attributed to the polymer-free micelle formation, whereas the second break is due to the polymer-bound micellar aggregates. However, no polymer-bound micellar aggregation process was observed in the case of TTAB + DTAB mixtures. Therefore, the presence of micelle-PVP interactions in the TTAB + HTAB case have been attributed to the stronger hydrophobicity of HTAB or TTAB + HTAB micelles in comparison to that of single or mixed micelles of TTAB + DTAB mixtures. From the conductivity data, various micelle parameters in the presence of PVP have been computed and discussed in terms of micelle-polymer interactions. The mixing behavior of TTAB + HTAB corresponding to the first break, and that of TTAB + DTAB mixtures in the presence of PVP, is close to ideal and is also identical to that in pure water.