Partitioning of a heterotelechelic polystyrene to separate interfaces of thin films

Heteratelechelic deuteropolystyrenes have been synthesised with a tertiary amine functionality at one end and a fluorocarbon group at the other end of the polymer chain. A layer of this polymer. circa 120 Angstrom thick, has been attached to the surface of a silicon substrate and subsequently covere d with a much thicker layer of hydrogenous polystyrene. The combination has then been annealed at 413 K under vacuum for defined times and the subsequ ent distribution of the deutero heterotelechelic polymer determined using n uclear reaction analysis and neutron reflectometry. The influences of annea ling time, molecular weight and thickness of the hydrogenous polymer have b een examined. Nuclear reaction analysis showed that an excess of the hetero telechelic polymer formed at both interfaces with a larger excess remaining at the substrate-polymer interface. When the molecular weight of the hydro genous polymer is lower than that of the deuteropolymer, the deutero layer is initially swollen by the hydrogenous polymer but the thickness then decr eases as deutero polymer becomes detached from the silicon substrate and an additional excess layer is eventually formed at the vacuum-polymer surface . When the molecular weight of the hydrogenous polymer is higher, there is an initial shrinkage of the deuteropolymer layer. but the original thicknes s (similar to radius of gyration of the. deuteropolymer) is regained on pro longed annealing. There is no evidence for bridging between the two interfa ces by the heterotelechelic polymer. After five days annealing the volume f raction distribution of the deuteropolymer at the silicon substrate was wel l described by a self-consistent field model where the only adjustable para meter was the sticking energy of the tertiary amine group to the silicon su bstrate for which a value of 8 k(B)T was obtained. Comparison of the depend ence of the equilibrium layer thickness of the deuteropolymer on the equili brium grafting density at the silicon surface with the predictions of scali ng theory for brush-like polymer layers suggested that the grafted molecule s were in the ideal, unperturbed brush region.