Optical and thermal characteristics of thin polymer and polhedral oligomeric silsesquioxane (POSS) filled polymer films

Single wavelength ellipsometry measurements at Brewster's angle provide a powerful technique for characterizing ultrathin polymeric films. By conducting the experiments in different ambient media, multiple incident media (MIM) ellipsometry, simultaneous determinations of a film's thickness and refractive index are possible. Poly(tert-butyl acrylate) (PtBA) films serve as a model system for the simultaneous determination of thickness and refractive index (1.45 at 632 nm). Thickness measurements on films of variable thickness agree with X-ray reflectivity results. The method is also applicable to spincoated films where refractive indices of PtBA, polystyrene and poly(methyl methacrylate) are found to agree with literature values within experimental error. Likewise, MIM ellipsometry is utilized to simultaneously obtain the refractive indices and thicknesses of thin films of trimethylsilylcellulose (TMSC), regenerated cellulose, and cellulose nanocrystals where Langmuir-Blodgett (LB) films of TMSC serve as a model system. Ellipsometry measurements not only provide thickness and optical constants of thin films, but can also detect thermally induced structural changes like surface glass transition temperatures (Tg) and layer deformation in LB-films. Understanding the thermal properties of the polymer thin films is crucial for designing nanoscale coatings, where thermal properties are expected to differ from their corresponding bulk properties because of greater fractional free volume in thin films and residual stresses that remain from film preparation. Polyhedral oligomeric silsesquioxane (POSS) derivatives may be useful as a nanofiller in nanocomposite formulations to enhance thermal properties. As a model system, thin films of trisilanolphenyl-POSS (TPP) and two different molar mass PtBA were prepared as blends by Y-type Langmuir-Blodgett film deposition. For comparison, bulk blends were prepared by solution casting and the samples were characterized via differential scanning calorimetry (DSC). Our observations show that surface Tg is depressed relative to bulk Tg and that magnitude of depression is molar mass dependent for pure PtBA films. By adding TPP as a nanofiller both bulk and surface Tg increase. Whereas, bulk Tg shows comparable increases for both molar masses, the increase in surface Tg for higher molar mass PtBA is greater than for lower molar mass PtBA. These studies show that POSS can serve as a model nanofiller for controlling Tg in nanoscale coatings.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Chemistry

Department dc:contributor.department

Chemistry

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2008

Author dc:creator

• Karabiyik, Ufuk

Chair dc:contributor.committeechair

• Esker, Alan R.

Committee members dc:contributor.committeemember

• Morris, John R.
• Ward, Thomas C.
• Troya, Diego
• Long, Timothy E.

• Polyhedral oligomeric silsesquioxanes (POSS)
• Refractive index
• Surface glass transition
• Langmuir-Blodgett films
• Polymer thin films

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-05142008-181528

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/27713