8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Fri 911:10-14:00P4.13Off-equilibrium response of grafted polymer chains atvariable rates of compressionChrister Elvingson, 1 Tobias Carlsson, 2 Gustavo Arteca, 2 and Natasha Kamerlin 11 Uppsala university, Department of physical chemistry, Ångströmlaboratoriet 751 05,Uppsala, Sweden2 Laurentian university, Sudbury, CanadaThe behaviour of confined macromolecules is important for a large number of practical applications[1] such as surface friction, biosensors and adhesives. A grafted material can act eitheras a protective layer or as a lubricant depending on how the confinement affects the intra- andinter-chain structure. Most theoretical work has concentrated on the equilibrium properties suchas density profiles or free energy changes under various types of confinement. There are, however,also dynamical simulations (e.g. [2]), which have investigated the relaxation and diffusionproperties of confined polymers. We have recently used Brownian dynamic simulations to lookat the microscopic response of grafted chains subject to compression, either by a rigid plane ora finite-size object. Starting at a very low surface coverage, we first investigated the response ofa single chain, varying the chain stiffness, the bead-bead interaction and the rate of compression.The analysis included chain size and shape, as well as chain orientation and intra-chain entanglement,and there was a clear difference in molecular response depending on the rate of compression,especially for ”hard mushrooms” [3]. We continued our study to finite surface coverages, lookingat the dynamics during compression of a polymer brush where we analyzed the intra-chain andinter-chain entanglement, as well as the concentration profiles, for different compression rates andsurface densities. Recently, we have extended these studies to also include the approach of twopolymer coated surfaces as well as the vertical and lateral motion of a model AFM-tip in a polymerbrush. [1] J. J. Kasianowicz, M. Kellermayer, and D. W. Deamer, Eds. Structure and dynamics ofconfined polymers, NATO Science Partnership Sub-Series: 3, vol. 87, Kluwer, Dordrecht, 2002.[2] D. Dimitrov, et. al. J. Chem. Phys. 128, 234902 (2008). [3] T. Carlsson, et. al. , Phys. Chem.Chem. Phys. , in press13