Title page for ETD etd-07202011-003445


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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