Effect of the Hydrophilic Block Length on the Surface-Active and Micellar Thermodynamic Properties of Oxyethylene-Oxybutylene Diblock Copolymers in Aqueous Solution

Abstract

The effect of hydrophilic block length on the surface and micellar thermodynamic properties of aqueous solution of E40 B8, E80B8, and E120 B8 diblock copolymers, were studied by surface tension measurements over a wide concentration and temperature range; where E stands for an oxyethylene unit and B for an oxybutylene unit. Like conventional surfactants, two breaks (change in the slope) were observed in the surface tension vs logarithm of concentration curve for all the three copolymers. Surface tension measurements were used to estimate surface excess concentrations (Γm), area per molecule at air/water interfaceA1s and thermodynamic parameters for adsorption of the pre-micellar region in the temperature range 20 to 50 ºC. Likewise the critical micelle concentration, CMC and thermodynamic parameters for micellization were also calculated for the post-micellar solutions at all temperatures. For comparison the thermodynamic parameters of adsorption and micellization are discussed in detail. The impact of varying E-block length and temperature on all calculated parameters are also discussed. This study shows the importance of hydrophobic-hydrophilic-balance (HHB) of copolymers on various surface and micellar properties.