Advances Toward the Synthesis of Low Temperature Expandable Microspheres (2013)

Undergraduates: Andrew Basinger, Natalia Lebedeva, Sergei Sheiko

Faculty Advisor: Sergei Sheiko
Department: Chemistry

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The purpose of this project is to synthesize expandable microspheres consisting of a core-shell morphology and a polymeric shell with a low glass transition temperature. The synthesis of polymer microspheres that expand at high temperatures is well-documented. This type of capsule expansion relies on blowing agent, glass transition temperature, and elastic properties of the shell; however, these systems undergo an irreversible transition upon expansion. Low temperature transitions with reversible expansion/deflation are desirable and would yield great potential in biological applications. The goal of this project is to prepare microcapsules with a polymeric shell having a low glass transition temperature to enable a controlled reversible expansion at ambient and body temperatures.
A Pickering Emulsion was utilized to generate microspheres composed of low glass transition acrylates and fluoropolymers. Perfluorohexane and perfluoropentane were selected as blowing agents for biological compatibility and boiling temperatures. Photoinitiation was required to keep the polymerizable solution at a low temperature in order to decrease vapor pressure. Results have shown it is difficult to prevent expansion in the synthesis process and that thermodynamics plays an important role in morphology of the particle. Surface tension measurements were used to identify thermodynamically favorable states and implemented variations on monomer generated differences in morphology.