CAREER: Dynamics, Rheology, and Microrheology of Rigid Polymers and Brownian Fibers

University Of Florida, Gainesville FL

Investigators

Abstract

Abstract CTS-0348205 J. Butler, U of Florida The general objective of the research program is to elucidate the dynamics and rheology of suspensions of Brownian rods while simultaneously developing microrheology as a tool for characterizing complex fluids containing rigid, Brownian particles. Improving the performance and creating new applications for materials made with rigid polymers and Brownian fibers partly relies upon the accurate determination of their physical properties. To characterize ridgid polymers and Brownian fibers, materials scientists and engineers measure quantities such as the particle diffusivities and fluid rheology. Interpretation of the results depends upon theories which usually provide qualitative scaling laws rather than quantitative predictions. To eliminate the disparity between quantitative predictions and measurements, a combined program of experimental and computational research is being pursued. The experimental program uses microrheology to evaluate the linear viscoelastic response of a suspension of isotropic Brownian rods and to measure the viscosity of a suspension of Brownian rods aligned by a shear flow. A direct comparison with measurements of standard shear-rheology will be made on the identical suspension. Simulations of the rheology and microrheology will be used in interpreting the measurements. These simulations will be the first rigorous and dynamic simulations for a suspension of Brownian fibers and rigid polymers which include multi-body hydrodynamic interactions. The results of the proposed experiments and simulations are anticipated to provide significant insight into not only the dynamics of Brownian fibers, but also the relationship between microrheology and macrorheology measurements. An integrated education program focused on incorporating stochastic processes and models into the undergraduate curriculum of chemical engineering will be carried out. The goal is to familiarize students with the fundamentals of random processes which are important to the emerging areas of biotechnology and nanotechnology; the current lack of these topics in the curriculum represents a critical barrier to the full participation of graduates of chemical engineering in these areas of technology. To address this significant issue, the PI is developing highly structured computer modules which will implement a system of self-study and take advantage of the simulation capabilities of the computer. The concepts will be presented using examples taken primarily from the area of biotechnology. This approach will provide the students with insights into fundamental processes associated with biotechnology while they simultaneously study the principles of stochastic processes. The modules will be used as teaching tools or supplementary material in existing courses. Once completed, the modules will be disseminated to educators through the internet and other available means. To further enhance the education of students, the PI is continuing to improve upon and expand the use of effective methods in teaching and is providing technical training and career counseling to students at all levels through direct participation in the research program. Broad Impact The significance of the proposed research is underlined by the improvement in the theories of semidilute solutions of Brownian rods which will result from the calculations. Rigid polymers are widely used as high performance plastics and examples of Brownian fibers can be found in the form of macromolecules of biological origin and in nanotechnology in the form of nanotubes and nanorods. Consequently, the research will have a direct impact on existing and emerging technologies in polymer science, nanotechnology, and biotechnology. The education program addresses the necessity of providing students with skills to participate in the emerging fields of biotechnology and nanotechnology. The development and implementation of the instructional tools will meet this need and create a technological workforce with appropriate training for participation in these new technologies. This effort will result in an enhanced educational experience and outcome for the students of the University; furthermore, the final products will be disseminated to other educators and therefore impact many additional students.