Effect of Hydrophilic/Hydrophobic Block Ratio and Temperature on the Surface and Associative Properties of Oxyethylene and Oxybutylene Diblock Copolymers in Aqueous Media

Abstract

Recent development in dispersion science and technology demands block copolymers with a variable block length and composition. To highlight that purpose, the surface active, associative, colloidal, and thermodynamic behavior of three diblock copolymers having different hydrophilic to hydrophobic ratio is reported here. Using surface tension and light scattering measurements, the micellization and adsorption behavior of polyoxyethylene and polyoxybutylene diblock copolymers of the type EmBn have been analyzed. Critical micelle concentration (CMC) and related thermodynamic parameters like free energy (ΔGmic), enthalpy (ΔHmic), and entropy (ΔSmic) of micellization were calculated from CMC value using the closed association model. Likewise, the surface active parameters, like surface excess concentration (Γ2), area per molecule (A2), and thermodynamic parameters such as free energy (ΔGads), enthalpy (ΔHads), and entropy (ΔSads) of adsorption of polymer at the air/water interface, were also calculated at various temperatures. Static and dynamic light scattering techniques were employed for the determination of the weight-average molar (Mw), association number (Nw), polymer–water interaction (A2), and micellar size in terms of hydrodynamic radii (Rh) of copolymer micelles. The effect of block length and solution temperature on the surface and micellar properties of these copolymers was also investigated.