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Open Access Dissertation
Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
Thomas J. McCarthy
Materials Chemistry | Polymer and Organic Materials | Polymer Chemistry
Five research projects described. First, a reproducible, lab-scale synthesis of MQ silicone copolymers is presented. MQ copolymers are commercially important materials that have been ignored by the academic community. One possible reason for this is the difficulty of controlling and reproducing the preparative copolymerizations that have been reported. A reproducible method for lab-scale preparation was developed that controls molecular weight by splitting the copolymerization into the discrete steps of sol growth from silicate precursor and end-capping by trimethylsiloxy groups. Characterization of MQ products implicates that they are composed of highly condensed, polycyclic structures.
The MQ copolymers prepared in the first project were observed to form tenacious emulsions and foams. This was an obvious indication of surface activity and led to further investigation. No open literature reports any measurements of MQ copolymers at interfaces. In this second project, selected MQ structures were studied at three interfaces: the air-water interface, the oil-water interface and the solid-air interface of supported MQ monolayers. The qualitative surface activity of MQ is confirmed and quantified. Residual silanols are found to be responsible for surfactantcy in MQ copolymers.
The third and fourth projects encompass research in Silicone-CNT composites. The first part of this work describes the ease with which CNTs can be dispersed into silicone matrices. Changes in silicone chemistry can improve CNT dispersion resulting in improved conductivities and mechanical reinforcement at CNT loadings of only fractions of a weight percent. The second portion of work on nanocomposites involves the discovery and investigation of the dramatic increase in thermal stability of silicone elastomers containing CNTs. Thermogravimetric analysis and pyrolysis gas chromatography-mass spectrometry indicate that the CNT network constrains silicone polymer chains and alters the mechanisms of decomposition.
The last project uses the Piers-Rubinsztajn reaction to rapidly and cleanly modify silicon oxide surfaces. This reaction has been studied very little as a method to modify surfaces and there has yet to be any work that measures dynamic contact angles on smooth surfaces. Trialkylsilane and methylsiloxane monolayers were prepared and analyzed. Monolayer densities are low in this reaction and result in anomalously low contact angle hysteresis for alkylsilane monolayers. Wetting properties in precise methylsiloxane polymer monolayers are shown to depend on graft structure. Dynamic contact lines from the liquid-like mobility of these grafts results in low contact angle hysteresis.
Flagg, Daniel H., "POLYORGANOSILOXANES: MOLECULAR NANOPARTICLES, NANOCOMPOSITES AND INTERFACES" (2017). Doctoral Dissertations. 1080.