Equilibrium concentration profiles of physically end tethered polystyrene molecules at the air-polymer interface

Abstract

Deuteriopolystyrene of molecular weight ca 32 000 g mol −1 has been functionalized at one end with a fluorocarbon. On mixing this polymer with 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 nuclear 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 enrichment theory, it is concluded that the deuteriopolystyrene is tethered by the fluorine label to the air surface. The parameters of this polymer ‘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 deuteriopolymer and the adsorption isotherm (surface excess at a function of equilibrium bulk volume fraction) have been compared to the predictions of a self-consistent field theory. Best agreement is obtained with a sticking energy of 1.6 k B T; however, there appear to be some disparities when compared to the limiting ‘dry’ brush predictions. There is evidence from neutron reflectometry of brush formation before annealing of the polymer films.