EQUILIBRIUM CONCENTRATION PROFILES OF PHYSICALLY END TETHERED POLYSTYRENE MOLECULES AT THE AIR-POLYMER INTERFACE

Deuteriopolystyrene of molecular weight ca 32000 g mol(-1) has been fu nctionalized at one end with a fluorocarbon. On mixing this polymer wi th an unfunctionalized hydrogenous polystyrene a surface excess layer of the deuteriopolymer forms on annealing at 423 K. The surface excess as a function of deuteriopolymer content has been obtained using nucl ear reaction analysis and neutron reflectometry, and the shape of the profile from neutron reflectometry alone. From previous secondary ion mass spectral data and by comparison with predictions of surface enric hment theory, it is concluded that the deuteriopolystyrene is tethered by the fluorine label to the air surface. The parameters of this poly mer 'brush' obtained experimentally are the surface volume fraction of labelled polymer, the brush height, the surface excess and the layer thickness. The surface excess and surface volume fraction of the deute riopolymer and the adsorption isotherm (surface excess at a function o f equilibrium bulk volume fraction) have been compared to the predicti ons of a self-consistent field theory. Best agreement is obtained with a sticking energy of 1.9 k(B)T; however, there appear to be some disp arities when compared to the limiting 'dry' brush predictions. There i s evidence from neutron reflectometry of brush formation before anneal ing of the polymer films. Copyright (C) 1996 Elsevier Science Ltd.