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/Co-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.