University of Connecticut |
Polymer Program SeminarPolymer Nanoengineering for Industrial and Biomedical Applications Friday, February 16, 2007 11:00 am , IMS Room 20 Polymer dynamics at the nanoscale is of importance in coatings, electronics, lithography, composites, and biocompatible materials. At the nanoscale, polymer-free surface and/or polymer-substrate interactions contribute greatly to the properties of polymers. Depending on the entropic and enthalpic effects of the interface, the nanoconfined polymer shows different thermomechanical behavior. In this work, we investigate substrate effects on polymer thin films as an analogy for polymer nanocomposites. Polystyrene (PS) thin films were spun-coat onto graphite and silicon oxide surfaces to resemble the polymer-substrate interface in carbon and organoclay based nanocomposites. The film thickness was varied and the apparent glass transition temperature (Tg) was investigated using atomic force microscope (AFM) with nanoparticles as the probe. The PS on these substrates shows different Tg profiles, depending on the polymer-substrate interactions. The influence of carbon dioxide (CO2) on the Tg profile of these thin films was examined as well. Neutron reflectivity and AFM studies show that introducing CO2, even at low pressures, largely enhances chain mobility and tends to alleviate the substrate confinement. These results provide valuable guidance for designing and processing new polymer nanocomposites. A low-temperature assembly method for polymeric micro/nanostructures has been developed based on low pressure CO2-enhanced chain mobility at the nanoscale. By regulating CO2 pressure, we successfully demonstrated the assembly of polymeric micro/nanostructures at low temperatures, even at biologically permissive temperatures. Furthermore, this assembly was realized in an aqueous environment in the presence of cells and biomolecules. Original structures are well preserved and CO2 pressure has little effect on the bioactivity/viability and functionalities of the proteins, DNAs, and cells studied. This CO2-assisted assembly method provides for a highly affordable manufacturing platform that, thus far, has been lacking in the fields of tissue engineering, cell-based biochips, cell therapy, and drug delivery.
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