Thermal and FTIR characterization of films obtained from carbopol/surfactant aqueous solutions

The suitability of differential scanning calorimetry (DSC) as a routine technique to characterize polymer/surfactant interactions in aqueous medium was evaluated in films obtained by evaporation of binary aqueous mixtures of Carbopol(R) 934, a cross-linked poly(acrylic acid), and Tween 80, Pluronic F-127 (non-ionic surfactants), sodium dodecylsulphate (SDS, anionic surfactant), or benzalkonium chloride (cationic surfactant). In all cases, the interactions that occur at specific proportions of both components, as shown in the FTIR spectra, could be detected by shifts of some melting peaks. Lorentzian deconvolution of carbopol carbonyl groups (1690 1730 cm(-1)) was used to quantify the intensity of the interaction between the polymer and the non-ionic surfactants. DSC curves revealed the compatibility of carbopol with Tween 80 or SDS, and its strong affinity for Pluronic F-127 or benzalkonium chloride. This surfactant binds electrostatically to carbopol causing the formation of an insoluble polyelectrolyte complex, the composition and thermal behavior of which are very different from those of the films obtained from the supernatant.