Light scattering and surface tensiometric studies of tip-modified PEO-PBO diblock copolymers in water

Abstract

The micellar and associative properties of four diblock copolymers, Me2N(CH2)2OE79B34 (denoted DE80B34), I−Me3N+(CH2)2OE79B34 (denoted TE80B34), I−Me3N+(CH2)2OE48B22 (denoted TE49B22), and HO(CH2)2OE62B22 (denoted E62B22), in aqueous solution and at various concentrations and temperatures, were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements enabled the critical micelle concentration (CMC) to be determined at different temperatures, and thus the enthalpy of micellization (ΔHomic), the free energy of micellization (ΔGomic), and the entropy of micellization (ΔSomic) to be ascertained. Dynamic and static light-scattering measurements allowed the micellar parameters to be calculated and the extent of hydration of the copolymer micelle to be obtained qualitatively. The experimental results provided by these techniques are discussed in the terms of the variation in the hydrophilic to hydrophobic (E/B) ratio and end-group modification. Micellar parameters such as the weight-average molar mass (Mw), the association number (Nw), the thermodynamic radius (rt), and the hydrodynamic radius (rh) obtained from light-scattering data show that the micelles formed by the conventional EmBn and dimethylamino-tipped (DEmBn) copolymers are harder than those of trimethylammonium-tipped (TEmBn) copolymers. This difference in micellar properties is considered to be due to differences in polarity and charge effect at the hydrophilic ends of the tip-modified copolymers. The high value of rh for DEmBn and TEmBn copolymers as compared to E62B22 is an indication of micellar aggregation.