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
- Polymer Melt
- Chain Migration
- No-slip Boundary Condition
- Lubrication forces
- Hydrodynamic forces
Date of Defense 2011-07-07 Availability unrestricted AbstractThe 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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