Influence of carboxymethylcellulose (NaCMC) on the aggregation and micellization behaviors in aqueous cethylpyridinium chloride solutions: Thermodynamic study and effect of polymer concentration

Abstract

In the present work, we applied Dynamic Light Scattering (DLS), conductivity and rheological measurements in order to assess the most important characteristics of the interaction between sodium carboxymethylcellulose (NaCMC) and cethylpyridinium chloride (CPCl). We evaluate the effect of temperature and weight-percentage concentration of added NaCMC on critical aggregation (cac) and CPCl-critical micellization concentrations (cmc*) for mixtures NaCMC/CPCl in aqueous solutions. Careful energetic analyses showed that micellization of CPCl in water is entropically driven and exothermic in presence of NaCMC, while for NaCMC/CPCl aggregation, enthalpic and entropic terms are both important. The process of forming micelle-decorated NaCMC skeletons at the cac is more favored by heating and less favored when we add more quantities of NaCMC at fixed temperature. DLS measurements allowed us to imagine a possible scenario of the aggregates shape-size evolution upon adding CPCl. We think that aggregates or “clusters” constructed by several micelle-decorated polymers linked by hydrophobic interaction are responsible of the hydrodynamic radius bump situated at the cac. These entities reach several hundreds of nm and are mainly monodisperse. Moreover, viscosity results showed that these aggregates interconnect by hydrophobic zones that form upon adding more CPCl which leads to a kind of network and probably explains the viscosity bump appearing just after that of hydrodynamic radius. We draw attention however to the role of shearing in the formation of this structure.