Surface properties of polymers and competition adsorption of toluene and heptane
on silica were studied using IR-visible sum frequency generation (SFG) vibrational
spectroscopy. SFG is intrinsically surface sensitive because the second-order optical
process is forbidden in media with inversion symmetry, such as bulk polymers and
liquids. This nonlinear optical technique provides surface vibrational spectra under
ambient conditions without the need of an ultra-high vacuum environment. Polymer
surface properties, including surface relaxation temperature of poly(methyl methacrylate)
(PMMA) and surface electronic states of poly[2-methoxy, 5-ethyl (2’-hexyloxy) para
phenylenevinylene] (MEH-PPV), were investigated. It was found that there are
significant differences between the surface and bulk properties for these polymers. For
PMMA, a new surface structure relaxation was identified at 67°C, which does not match
any known structure relaxation temperatures for bulk PMMA and is 40°C below the bulk
glass transition temperature. For MEH-PPV, SFG electronic spectra, which were
obtained by scanning the frequencies of incident visible and JR beams, indicated that the
electronic states at the polymer/solid and air/polymer interfaces are red-shifted with
respect to that of the bulk. Finally, SFG was employed to study the competition
adsorption of toluene and heptane on silica surfaces. Experimental data showed that
heptane adsorbed favorably compared to toluene. Using a Langmuir adsorption isotherm,
the changes of Gibbs free energy for the adsorption processes were calculated to be —12.1
± 1.8 (kJ/mol) for toluene and —16.5 ± 2.3 (kJ/mol) for heptane.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/2834 |
| Date | 11 1900 |
| Creators | Hua, Rui |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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