Formation of polymer – hexadecylpyridinium chloride complexes using different structures of poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA), a strategic biodegradable and biocompatible polymer, can interact with surfactants to provide desirable properties in several applications, such as in cosmetics formulation. Here, the interaction process between hexadecylpyridinium chloride (C16PyCl) surfactant and different structures of PVA were investigated using conductivity, turbidimetry, and isothermal titration calorimetry (ITC). Figure 1 shows the results obtained for the titration of C16PyCl into water with or without PVA (hydroxylated, PVOH, or carboxylated, PVCOOH). The critical micellar concentration (cmc) of the C16PyCl was (1.03 ± 0.03) mmol L-1 (Figure 1a). In the presence of PVOH, the surfactant interacted with the polymer, and the critical aggregation concentration (cac) was (0.8 ± 0.1) mmol L-1. In PVCOOH solution, the aggregation process was observed at concentrations smaller than 0.1 mM, indicating a more favorable interaction between the C16PyCl and the carboxylated PVA. This result came from the more intense electrostatic interactions between the surfactant (positively charged) and the PVCOOH, more negatively charged than the PVOH. The formation of C16Py+-PVCOO- complexes was accompanied by phase separation due the formation of a precipitate that was dissolved at higher surfactant concentration (Figure 1b). Interestingly, for both polymers, ITC results (Figure 1C) showed that the Δ???? values were lower when PVA was not present into the calorimetric cell, indicating that the polymer-surfactant interaction was endothermic, and suggesting the incorporation of the PVA in the surfactant aggregate.