(43c) Preparation of Structured Polymer Composites Using an Ultrasonic Focusing Technique

Our research aims to develop polymer composites in which the geometric configuration of sub-micron sized particle inclusions is actively controlled. Previous research in our laboratory has shown that ultrasonic standing wave fields can be used to precisely position particles suspended within fluids. Starting from an unstructured suspension, the particles can be organized into bands or layers provided that there is a difference in the acoustic properties of the particles relative to their suspending fluid. For a one-dimensional ultrasonic field, particles can be organized into evenly spaced bands oriented perpendicular to the propagation direction of the field. More complicated spatial arrangements result from multi-dimensional acoustic fields. In the current application, particles are suspended within a monomer and the acoustic field is applied to organize the particles into a desired configuration. While the acoustic field is activated, a polymerization reaction is initiated. Once polymerization is complete, the particle structures produced by the ultrasonic fields are preserved. The properties of the resulting composite can then studied using microscopy or other analytical techniques. Our experiments have shown that it is possible to focus micron sized particles, such as carbon and silica into bands, and then freeze the structures in methacrylate and Teflon like polymers. Preliminary results show that it may be possible to extend the technique to the case of nano-sized particles in various polymers. Our ultimate goal is to produce one and two-dimensional particle structures in polymers for applications including advanced membranes, barrier materials, and other structured nanocomposites. For example, banded particle structures within thin polymer films may provide a way to improve its mechanical and transport properties in comparison to a composite film with a random particle structure. The scope of our current work explores the fundamental relationships between particle characteristics, acoustic parameters, and effects of the polymer matrix, to determine how they affect the acoustic focusing process.