Chain conformation and phase behavior in polymer blend thin films

Open Access
Author:
Jones, Ronald Leland
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 29, 2002
Committee Members:
  • Jayanth R Banavar, Committee Member
  • David Lawrence Allara, Committee Member
  • Sanat Kumar, Committee Chair
  • Ralph H Colby, Committee Member
Keywords:
  • neutron scattering
  • finite size effects
  • polymer thin films
Abstract:
The properties of thin films are expected to deviate from bulk analogs as film thickness decreases toward molecular dimensions, however the precise length scales associated with these changes and the resulting magnitude of the effects are generally not known. In this work, we probe the effects of confinement within a polymer thin film, focusing on the properties of chain conformation and phase miscibility. To study these properties within films possessing micrograms or less of material, the technique of Small Angle Neutron Scattering (SANS) is extended from a purely bulk technique to a reliable measurements of polymer films with a total thickness less than a single radius of gyration (R$_{G,Bulk}$). Addressing a 50 year old debate, molecular shape and size are found to retain their bulk values, even in highly confined thin films. When measurement error is considered, this result is consistent with theoretical predictions of only small ($<$10\%) expansion along the substrate plane. In stark contrast to theoretical predictions, the phase boundary, represented by the binodal, is found to also remain independent of film thickness. The scattered intensity, however, is both thickness and temperature dependent. Using conventional mean-field models, we demonstrate that this dependence is not addressed by current theories of phase behavior in finite sized systems. Additional studies are presented concerning the effects of thermal history on morphology and surface flexibility on miscibility.