Defense Date

2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Dr. Kenneth J. Wynne

Abstract

The goal of this research is to cover a broad set of scientific investigations of elastomeric materials based on polydimethylsiloxane (PDMS) and poly((3,3,3-trifluoroethoxymethyl)methyloxetane) diol. The scope of study covers five areas, well correlated with each other. The first study investigates the near surface morphology of condensation cured PDMS as a function of increasing the amount of siliceous phase. The appearance, disappearance and reappearance of untreated fumed silica nanoparticles at the PDMS near surface and their correlation with the volume fraction of siliceous phase have been studied. This research with PDMS nanocomposites has led to the development of an alternative route for improving mechanical strength of PDMS elastomers, conventionally known to have weak mechanical properties. The second study involves synthesis of a triblock copolymer comprising of four mutually immiscible phases, namely, soft segments comprising of fluorous and silicone domains, a diisocyanate hard segment and a glassy siliceous phase. Structure-property relationship has been established with an investigation of the interesting surface and bulk morphology. The highly improved mechanical strength of these soft materials is noteworthy. The dominance of silicone soft block at the triblock near surface has led to the third study which investigates their potential non-adhesive or abhesive characteristic in both a laboratory scale and in a marine environment. The peak removal stress and the removal energy associated with the detachment of a rigid object from the surface of these triblock copolymers have been measured. Results obtained from laboratory scale experiments have been verified by static immersion tests performed in the marine environment, involving the removal of adhered soft and hard fouling organisms. Gaining insights on the characteristics of an easy release surface, namely low surface energy and a low near surface modulus, a new way for controlling the near surface composition for elastomeric coatings have been developed. This technique involves an elastomer end-capped with a siliceous crosslinking agent and a tough, linear polyurethane. The basic concept behind the hybrid compositions is to develop a coating suitable for foul release applications, having a low energy surface, low surface modulus but good bulk mechanical strength. Henceforth, the fourth study deals with synthesis and characterization of the hybrid polymers over a wide range of composition and investigates their foul release characteristic in laborartory scale experiments. In our final study, attempts have been made in generating a silicone coating with antimicrobial property. A quaternary alkylammonium in different weight percents have been incorporated into a conventional, condensation cured polydimethylsiloxane (PDMS) elastomer. Antimicrobial assay has been performed on these modified silicone coatings to assess their biocidal activity against strains of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Surface accessibility of quaternary charges has been quantified by measuring the streaming potential of a modified coating. An effort has been made in improving the mechanical strength of the weak PDMS elastomers by adding treated fumed silica nanoparticles as reinforcements. The effect of adding fillers on the mechanical property (tensile), surface concentration of quaternary charge and on the biocidal activity of a representative sample has been investigated.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2012

Included in

Engineering Commons

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