The research objective of this Early Faculty Career Development (CAREER) award is to develop a new method to tailor the properties of liquid suspensions and nanocomposites by controlling the organization of nanoparticles during processing. Current materials that are made with carbon nanotubes and other nanoparticles are limited by a lack of tailored microstructure properties. This is seen especially in the lack of particle dispersion control. By controlling the microstructure, properties like suspension viscosity can be altered along with other composite properties including electrical conductivity, strength and degradation temperature. In order to control the microscopic properties of a set of model nanoparticles, light, pH and temperature stimuli responsive polymers will be used.
This methodology and its results are important because it will demonstrate design methods to control nanoparticle dispersion in liquid dispersions. This is important for biomedical applications. In addition, the control of microstructure properties creates a new class of lightweight engineering composites that will have applications in microwave antenna substrates, sensing and actuation transducers for biomedical applications and highly conductive flexible microelectronic materials. The educational objectives of this award include outreach to high school students as well as undergraduate students. Minority high school students will be included in the research via collaboration on science fair projects related to the research. Experiments in microstructure will be integrated into undergraduate coursework that will be developed as well as direct involvement of undergraduates in the research project as well.
Materials currentlybeing made with carbon nanotubes and other useful nanoparticles are limited by a lack of microstructural control (i.e., how the particles are dispersed/organized within the material). This project has made significant strides in overcoming this challenge using pH-responsive (i.e., weak polyelectrolytes) and thermoresponsive polymers, whose molecular shape changes with pH or temperature. Dispersion of single-walled carbon nanotubes (SWNT) in water with polymers allows precise tailoring of the nanoparticle dispersion state as a function of pH or temperature, ranging from highly dispersed to highly aggregated. These microstructural variations dramatically alter aqueous suspension viscosity and dry nanocomposite properties such as electrical conductivity. Now we are beginning to see if the same control of microstructure can be accomplished using light-responsive polymers. Additionally, we have had some success producing thermoelectric (i.e., converting waste heat to useful electricity) polymer nanocomposites. To-date we have produced the best thermoelectrics ever produced using polymeric materials, according to the open literature. Our initial publications in Nano Letters (2008) and ACS Nano (2010), two of the top nano-materials journals, are likely to encourage others to join this effort. Composites with high thermoelectric efficiency could lead to tremendous energy savings. It was the NSF CAREER funding that provided the seed money needed to undertake this work, which builds upon our ability to effectively stabilize nanotubes in water. We envision walls being covered with thermoelectric paint that would convert wasted body heat into enough electricity to power the room’s lighting (or a t-shirt that would harness enough body heat to power your cell phone). Other applications that will be influenced by this NSF-sponsored research include microwave antennas, sensors and actuators. Additionally, tailoring the dispersion state of nanoparticles in liquid suspensions is useful for a variety of biomedical applications, including new methods of drug delivery. All graduate, undergraduate, and middle school students involved in activities related to this CAREER award have gained a positive perspective toward engineering research. The two PhD students funded by this project (Lei Liu and Krishna Etika) have gone on to become productive scientists in society (one at Case Western Reserve University and the other at Intel). Andrew Stephenson, one of several undergraduates that worked on this project, is serving in the military, but he is now interested in graduate school in mechanical engineering or materials science. Lance Hess, Michael Cox and Katherine Sun participated on this project as REU students and are now applying (or already have applied) to graduate school. In all, more than ten undergraduate students participated in hands on research made possible through this NSF funding. The middle school children I've been exposed to, in the context of science project mentorship related to this NSF funding, are all interested in being engineers or scientists in the future. Many of these students have been women and/or minorities. Obtaining the CAREER award has allowed me to leverage additional funds from Texas A&M University to purchase new materials characterization equipment. More specifically, we purchased a high performance rheometer capable of measuring viscosity as a function of temperature and strain rate, which will enhance our ability to conduct the CAREER-related research and contribute to other ongoing projects at Texas A&M. This and other related equipment has gone on to benefit industrially-funded work that will ultimately help the economy through new products. None of this would have been possible without the NSF funding as a starting point.
