This Small Business Technology Transfer (STTR) Phase II project aims to develop a method for rapid, direct and large-scale production of pristine nano-graphene platelets (NGPs). A combined molecular dynamic, macroscopic modeling and experimental approach will be used to (1) further improve the understanding of the underlying principles behind effective peeling of single-layer graphene sheets from graphite particles in selected liquid mediums, and (2) to clearly determine the most critical processing conditions that govern the graphene production rate in a continuous processing reactor.
The broader/commercial impacts of this project will be the potential to offer a cost-effective method to produce pristine nano-graphene in large quantities. NGPs are of exceptional scientific and technological significance. The ability to produce large-volume pristine nano-graphene will have a profound impact on the evolution of nano-graphene science and technology. Highly conductive graphene may find practical applications in transparent and conductive coating, supercapacitor, battery electrode, fuel cell bipolar plates, and conductive nanocomposite.
Graphene and graphene-oxide are novel, 2 dimensional, and few-nanometer-thick materials based on flat honeycomb structure made from carbon atoms. These materials are among the ones whose production and manipulation have become possible during the last decade, owing to the advancements in materials production, processing, and characterization at very small scales (~40,000 times smaller than the width of an average human hair). Such capabilities have opened categorically new opportunities for technological advancements in areas ranging from energy to healthcare to electronics, to name just a few. Efficient production methods, and a deep knowledge on how they work, are essential for utilization of these new materials. The most critical processing conditions for making these materials have been identified and effects of these parameters on properties of the produced materials have been justified. As an outcome, a simple sonication method has been developed for large-scale production of pristine graphene and its oxide form (graphene oxide). The products developed in this project, using these new materials, include flexible graphene sheets. The thickness of graphene sheets is controllable in the range between tens of micrometers and few millimeters. Independent of their thickness, these sheets are highly flexible. The in-plane electrical and thermal conductivities of these graphene sheets were measured to be around 3,000 S/cm and 900 W/mK, respectively, much higher than those of commercial flexible graphite sheets (typically only 1,500 S/cm and 500 W/mK). When tested in smart phones, graphene-based sheets outperform the conventional heat spreader in heat management. The subcontractor contribution to this project has focused on understanding production of graphene and graphene oxide using computer simulations. The initial structures that are readily available contain stacks of many layers of flat honeycomb structures, one sitting on top of another. These stacked materials are put in liquid solvent and stirred in order to produce single layer (or few layers) of honeycomb structures. Computer simulations have assessed this process by including several relevant factors such as solvent type and honeycomb configurations, and by calculating the details of production process. The project revealed that among different possible mechanisms a step-by-step separation procedure is the most feasible. The roles of various relevant parameters were also explored. These results help in understanding the efficiency of production mechanisms, and are important for insightful selection of production conditions and materials in order to achieve better production results. The simulation part of the project has had a significant educational outcome with four graduate students, partially supported by the project, working on different parts of the research. The simulations have resulted in two technical papers based on the project outcomes. These are being reviewed for publication in corresponding research journals.
