Temperature dependence of solution properties of anionic polyelectrolyte-cationic surfactant complexes in ethanol

Stoichiometric polyelectrolyte-surfactant complexes, PSCs, were prepared from poly(acrylate), PA(-), and poly(styrenesulfonate), PSS-, anions and dodecyltrimethylammonium cations, DTA(+), and their properties were investigated by density and viscosity measurements in ethanol solutions in dependence on concentration and temperature. The measured densities were used to calculate the apparent molar volumes of the repeat units of DTAPA and DTAPSS complexes. Apparent molar volumes at infinite dilution, so as the reduced viscosities, in ethanol solutions are only weakly dependent on temperature. Through features typical for polyelectrolytes, viscosity curves suggest some small dissociation of complexes in ethanol. Light scattering, LS, measurements performed in the angular range from 50 to 150 degrees did not reveal so called slow relaxation mode, which is typical for strongly charged polyelectrolytes in aqueous solutions without or with only a low amount of added salt. Size distributions were therefore calculated from the measured correlation functions. They were multimodal at all angles and for both PSCs, identifying 3 populations: particles with average hydrodynamic radii (i) below 10 nm, (ii) in the range 20-30 nm, and (iii) in the range 200-300 nm. Analysis of angular dependency of LS intensity for the largest particle population enabled the determination of the radius of gyration and the shape parameter p of these species. Large sizes, p values (p = 1.6 and 1.9 for DTAPA and DTAPSS, respectively), and the Kratky plots of the scattering data suggest that these particles are associates of more than one PSC (reverse micelle). Dynamic vapor sorption experiments with thin films of the studied PSCs show that the DTAPSS complex absorbs at the most 35% of water per its weight, whereas the DTAPA one absorbs considerably more (around 75%). Different structure of complexes was taken as responsible for large differences in water uptake. (C) 2016 Elsevier B.V. All rights reserved.