Analysis of compression of polymer mushrooms using self-consistent field theory.

A number of new technologies, including new-generation biomaterials and chromatography resins, are based on passivation and modification of surfaces by terminally attaching polymer chains to the surface. However, little is known about these systems at the molecular level. In this work the compression of a single end-grafted polymer chain (or mushroom) by a disc of finite radius was investigated using a self-consistent field (SCF) lattice model. In accordance with results predicted using scaling theory [Subramanian et al., Europhys. Lett. 29 (1995) 285 and Macromolecules 29 (1996) 4045], the compressed chain undergoes a smooth escape transition. However, under the assumption of angular symmetry, a first-order escape transition of the end-grafted chain is not observed, suggesting that the formation of a tether is required for the predicted phase transition. Segment density distributions and compression energies are calculated in a cylindrical lattice. The energy required to compress a chain increases monotonically as the disc is moved closer to the surface and becomes independent of chain length at strong compressions where the work of compression involves only confinement of the tether joining the escaped chain fraction to the grafting point.