Abstract
The thermodynamics of micelle formation by a polystyrene- b-polyisoprene block copolymer in n-hexadecane, which is a selectively bad solvent for polystyrene, has been investigated. The temperature dependence of the critical micelle concentration (c.m.c.) was determined from measurements of scattering intensity against temperature carried out at seven concentrations within the range (1.24–3.25) × 10 −4 mol dm −3. A plot of 1n (c.m.c.) against T −1 gave a value for the standard enthalpy of micellisation of −40.7 ± 2.2 kJ mol −1 of copolymer chains. The standard entropy contribution ( −TΔS ⊖ ) to the standard free energy of micellisation was found to be positive. The results are in strong contrast to those reported for synthetic surfactants in aqueous media below 50°C for which a favourable standard entropy change is the factor mainly responsible for micelle formation.
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