The Adsorption of a Polystyrene‐b‐Polyisoprene Block Copolymer at the n‐Hexadecane/Air Interface

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Abstract
Surface‐tension measurements were used to investigate the surface adsorption and micellisation of a polystyrene‐b‐polyisoprene block copolymer in n‐hexadecane which is a selectively bad solvent for polystyrene. Measurements were made over a range of concentrations (1.29–2.88)x10−4 mol dm−3 and temperatures 25–40°C. The block copolymer was found to be positively adsorbed at the n‐hexadecane/air interface. The linearity of plots of γ against In c just below the critical micelle concentration (c.m.c.) indicated an approximately constant surface concentration. The area per block copolymer molecule at the surface had an average value of 4.1 nm2. A plot of In (c.m.c.) against T−1 gave a value for the standard enthalpy of micellisation of ‐41.9.3.0 kJ per mole of copolymer chains. The standard entropy contribution (‐TΔSΔ) to the standard free energy of micellisation was found to be 19.7.3.0 kJ mol−1. These thermodynamic values are in good agreement with results obtained earlier for this system by light scattering and calorimetry.