Interactions of water-soluble polymers with small molecules II: Poly(2-diethylaminoethyl methacrylate)-methyl orange and its homolog systems at different temperatures

Abstract

In order to investigate the interactions of poly(2-diethylaminoethyl methacrylate) (PDEAEMA) with methyl orange and its homologs in solution, temperature dependence of the complex formation has been examined in detail by the measurements of transmittance and specific conductance for the systems. Furthermore, the binding course of dyes to PDEAEMA has been studied on the basis of thermodynamic parameters obtained from equilibrium dialysis experiments at different temperatures. It was observed that the flocculation process shifted to lower dye concentrations in accordance with increasing hydrophobicity of the dyes in the order, methyl orange < ethyl orange < butyl orange, and the process of complex formation was characterized by three separate regions according to the slope of specific conductivity-mixing ratio curve for mixtures of PDEAEMA and dye. The temperature dependences of ΔF,ΔH and ΔS suggest that, for dyes-PDEAEMA complex formation, the hydrophobic interaction is predominant at a low temperature but the electrostatic interaction becomes important as the temperature increases.