Nanorheology of adsorbed diblock copolymer layers

Abstract

We investigate the mechanical properties of ultra-thin layers of polystyrene/poly (2-vinylpyridine) (PS/P2VP) block copolymers by means of a Surface Forces Apparatus adapted to operate asa rheometer at the molecular level. Two systems are studied: ''brush/wall'' and ''brush/brush''. A comparison of the normal force curves shows that when brushes are compressed against each other, they contract rather than interpenetrate. Nanorheological experiments have been carried out on both systems but reliable measurements have been obtained only on the brush/wall system. The complex shear modulus, characterizing the confined medium, has been measured as a function of separation. Its distance dependence is compared with a scaling model describing the linear shear behaviour of a brush confined by a neutral surface.