Calorimetric study on interaction of water-soluble copolymers with ionic surfactant

Abstract

Using isothermal titration microcalorimetry (ITC), we examined the aggregation behavior of water-soluble copolymers, poly(methoxypolyethylene glycol methacrylate- co-ethyl acrylate)s (PME-EA)s, with ionic surfactant, sodium dodecyl sulfate (SDS). From ITC measurements the values of critical aggregation concentration (cac) and saturation concentration ( C 2 ), the concentration at which the aggregation of the copolymers starts to form and reaches saturation, respectively, were determined. Thermodynamic parameters such as Δ G agg 0 , Δ H agg , and T Δ S agg 0 of the aggregation were deduced. Results indicate that cac of the PME-EA remained constant with increase in the concentration of the copolymers, while C 2 increased linearly. On the other hand, the effect of the weight ratio of the EA unit in the copolymer was such that cac of the PME400-EA decreased, while C 2 increased with increase in the weight ratio. The results suggested that the EA units are the main binding sites of the copolymer with SDS.