Synthesis and Characterization of Crosslinked Polysiloxane-Clay Nanocomposites for Uses in Skin Care Products

by Nelson, Tiffany S.

Abstract (Summary)
Polysiloxane-clay nanocomposites were synthesized to determine their effectiveness as a sun blocking gel. This was done by incorporating 15A cloisite clay and TiO2 with crosslinked polydimethylsiloxane (PDMS). The PDMS hybrid system was processed via hydrosilylation reaction between vinyl terminated PDMS and polymethylhydrosiloxane (PMHS). After adding the catalyst, 2% dodecylbenzene sulfonic acid Na^+ salt solution, the samples were heated, signifying the start of the reaction. After the reaction was inhibited, a solvent was added to facilitate the products into forming into their prospective gel composition. The synthesized products varied in PMHS crosslinker concentration, filler concentration, and solvent concentration. Analysis of the samples included FTIR, which aided in determining the functional group presence, calculating hydrosilylation kinetic rate parameters, and concluding whether or not the filler concentration affected crosslinking and postcuring rates. UV/visible analysis was performed on the crosslinked samples to determine the products’ UV absorbing ability. X-ray diffraction was carried out in order to understand the dispersion type and particle filler morphology. Brookfield viscometry studies determined the viscosity as a function of shear rate, shear stress, and temperature. Ubbelholde dilute solution viscometry was done to give a molecular weight range for the samples. FTIR results concluded that the system was crosslinked using the catalyst with no known byproducts created. However, it was observed that the reaction rate decreased for samples that contained filler. Kinetic studies revealed that the hydrosilylation reaction was a second- order reaction. XRD plots indicated that exfoliation was achieved between the polymer and clay, and UV absorbing intensity was increased compared to samples containing only TiO2 dispersed in PDMS that had not been crosslinked. Ubbelholde viscosity studies determined that the samples containing no filler had the highest molecular weight, while the sample containing the highest filler load had the lowest molecular weight. Brookfield viscometry results indicated that the viscosity of the neat PDMS, unreacted PDMS/ 15A/ TiO2, and crosslinked products increased as the shear stress and shear rate increased.
Bibliographical Information:


School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:nanocomposites polysiloxanes clay sunscreens silicones


Date of Publication:01/01/2006

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