Type of Document	Master's Thesis
Author	Chatchaidech, Ratthaporn
URN	etd-07202011-003445
Title	Lubrication Forces in Polydimethylsiloxane (PDMS) Melts
Degree	Master of Science
Department	Chemical Engineering
Advisory Committee	Advisor Name Title Ducker, William A. Committee Chair Davis, Richey M. Committee Member Walz, John Y. Committee Member
Keywords	Solid-Liquid Interface AFM Polymer Melt Chain Migration No-slip Boundary Condition Lubrication forces Hydrodynamic forces
Date of Defense	2011-07-07
Availability	unrestricted
Abstract The flow properties of polydimethylsiloxane (PDMS) melts at room temperature were studied by measurement of lubrication forces using an Atomic Force Microscopy (AFM) colloidal force probe. A glass probe was driven toward a glass plate at piezo drive rates in the range of 12 – 120 μm/s, which produced shear rates up to ~104 s-1. The forces on the probe and the separation from the plate were measured. Two hypotheses were examined: (1) when a hydrophilic glass is immersed in a flow of polymer melt, does a thin layer of water form at the glass surface to lubricate the flow of polymer and (2) when a polymer melt is subject under a shear stress, do molecules within the melt spatially redistribute to form a lubrication layer of smaller molecules at the solid surface to enhance the flow? To examine the effect of a water lubrication layer, forces were compared in the presence and the absence of a thin water layer. The presence of the water layer was controlled by hydrophobization of the solid. In the second part, the possibility of forming a lubrication layer during shear was examined. Three polymer melts were compared: octamethyltrisiloxane (OMTS, n = 3), PDMS (n avg = 322), and a mixture of 70 weight% PDMS and 30 weight% OMTS. We examined whether the spatial variation in the composition of the polymer melt would occur to relieve the shear stress. The prediction was that the trimer (OMTS) would become concentrated in the high shear stress region in the thin film, thereby decreasing the viscosity in that region, and mitigating the shear stress.
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