Thermodynamics of micellisation of a diblock copolymer of ethylene oxide and styrene oxide in water

Abstract

Aqueous solutions of block copolymer S₁₃E₆₀ were studied by surface tensiometry. [E denotes an oxyethylene unit, OCH₂CH₂ , and S an oxyphenylethylene unit, OCH₂CH(C₆H₅).] Critical micelle concentrations were determined at several temperatures and thereby values of the standard enthalpy of micellisation, Δ_micH°. It was found that the copolymer underwent almost athermal micellisation. This unusual behaviour in block copolymer systems is attributed to the hydrophobic block being tightly coiled in the molecular state, so that interaction of its units with water (hydrophobic bonding) is minimised, with the resulting small positive contribution to Δ_micH° being essentially balanced by a negative contribution from dispersion interactions of B units in the micelle core.