Single-layer graphite, known as graphene, has taken center-stage as a revolutionary new nanomaterial in recent years due to its excellent mechanical, thermal, and electrical properties, including the capability for several unusual quantum effects. Graphene shows great promise as the basis for novel multifunctional materials, including field effect transistors, flexible electronics, transparent thin films, nanocomposite fillers, and structural carbon fiber. Many of these materials and devices require scalable, liquid-phase processing. However, development of such materials has been hampered by fundamental scientific challenges associated with each processing step (1) Difficult dispersion due to poor exfoliation and rapid re-aggregation of graphene sheets, (2) poor interfacial adhesion between filler and matrix, (3) poor understanding of bulk processing, particularly in regard to graphene rheology and microstructure. Prior studies have utilized chemically modified graphene with properties far inferior to pristine graphene. The goal of this program is to overcome these processing challenges for pristine graphene-based materials. We generate pristine graphene sheets encapsulated in a polymer nano-coating through localized polymerization on the graphene surface, as demonstrated through successful preliminary proof-of-principle experiments. This technique results in stabilization against aggregation and will be demonstrated by effective incorporation into polymer nanocomposites. We also create innovative studies in the novel field of graphene rheology in order to enable controlled graphene processing. We compare experimental rheometric results against simulations of the microstructure-rheology model for discotic solutions. Preliminary simulation results show promising results for modeling alignment dynamics. Intellectual merit: This transformative engineering plan meets three critical scientific challenges in the graphene community. Novel interfacial polymerization techniques are generated for (1) the production of re-dispersible, pristine graphene, which has never been attained before. Furthermore, polymer coating allows (2) the precise engineering of the interface between graphene and the polymer matrix in nanocomposites to increase interfacial strength. This approach is groundbreaking because it avoids the degraded properties associated with the commonly-used graphite oxide processing route. This program also pioneers the novel field of (3) graphene rheology and correlates rheological properties with graphene alignment and dispersion quality through a combination of experimental and computational studies. Broader impacts: Although this program focuses on the fundamentals of graphene dispersion, interfacial chemistry, and rheology, these findings have immediate application to the wide range of graphene-based materials and devices in need of bulk liquid-phase processing, including electronic devices, composites, and films. Thus, this interdisciplinary program combines fundamental scientific research with practical engineering applications. The findings will be disseminated on the broad scale through presentations and publications and on the local scale through the PI's functional materials course. Broadening Participation: The program seeks to integrate research and education by engaging undergraduate researchers and a high-school teacher with a central role in problem design and visualization for the simulation aspects of the work. In concert with these research efforts, the PI and the high school teacher will partner with the TTU T-STEM Center to create, evaluate, field-test, and disseminate nanotechnology curriculum for use in STEM education for grades 9-12. The curriculum uses both scientific and ethical challenges in nanotechnology as a platform for student-driven research projects and debates. This curriculum will emphasize student inquiry and active learning in order to provide deeper investigation and learning and generate increased interest in STEM fields among underrepresented groups. This curriculum creates new motivation and enthusiasm in STEM fields by emphasizing the potential for nanotechnology to be used for environmental responsibility and social justice (e.g., oil spill clean-up, water purification in developing countries); such topics are often neglected in STEM education and will engage a broader spectrum of student backgrounds.
The outcomes of this project cover advancements in both the science of graphene processing as well as efforts to broaden participation in STEM field. Graphene, i.e. single-layer graphene, is a two-dimensional carbon nanomaterial with a number of promising applications in advanced materials. In this project, our research efforts followed several broad areas: (1) We aimed to develop techniques for creating polymer coatings on the surface of dispersed pristine graphene. Most prior work in the area of dispersed graphene involves the use of covalent functionalization to enable graphene dispersion. Our focus is on the use of non-covalent polymer coatings. We examined the use of both polymer (polyvinylpyrrolidone) physisorption on exfoliated graphene and the use of interfacial in situ polymerization to create nylon coatings on graphene (Figure 1). In both cases (polymer physisorption and in situ polymerization), the interaction with graphene is non-covalent, which preserves graphene’s basal plane and electrical properties. This work has since been extended to cover a number of novel dispersants for pristine graphene in solution. We also demonstrated that such dispersions can applied to the field of graphene-polymer composites for solution-cast fibers and films as well as thermosets (Figure 2). (2) We have also examined the rheology of nanomaterial dispersions, both at the dilute level and at high concentration (liquid crystalline) systems. In particular, simulations of liquid crystalline systems indicate that the anisotropy of anchoring boundaries can have substantial effects on flow-microstructure coupling in nanomaterial liquid crystals, particularly as chiral effects increase (Figure 3). We also examined the effects of spherical particles (common synthesis byproducts) on the concentration phase boundaries for the isotropic-nematic transition in anisotropic nanomaterials. Broadening participation efforts centered on the following thrusts: (1) A Research Experience for Teachers (RET) program allowed local high school mathematics teachers to work with the PI in the areas of curriculum development and simulations of nanomaterial rheology. These efforts resulted in nanotechnology curriculum for use in grades 9-12 and a "History of Engineering" curriculum for use in freshman level collegiate courses. These efforts were applied through collaboration with New Deal High School in New Deal, Texas. (2) Research Experience for Undergraduates allowed undergraduate researchers to be highly involved in the research aspects of this project. This involvement deepens the undergraduate educational experience and can allow undergraduates to explore the possibilities of graduate and a research-focused career. Outcomes on this front include first place in the 2011 National AIChE Student Paper Competition as well. Four undergraduate students were co-authors on publications resulting from this award. Most notably, one publication had an undergraduate researcher as first author, and a RET teacher as second author; this level of success and involvement from RET and REU programs is rare.
