The objective of the proposed research is to promote a multi-disciplinary collaboration between theorists and experimentalists to understand and develop active nanostructured architectures such as nanocomposite skins and films that do not require any piezoelectric materials as constituents and in principle can be designed with any material combination. Modeling methods ranging from ab initio atomistic calculations to enriched continuum models will be employed to enhance understanding of flexoelectricity at the nanoscale and provide guidelines to select materials and engineer highly optimized, apparently piezoelectric nanostructures with the requisite symmetry, topology and size. The different topologies will be fabricated by precisely controlling the dispersion of suitably shaped nanoparticles in a polymer matrix (from soft elastomers to hard thermoplastics and thermosets) with external fields (flow, electrical & magnetic) as a means to tune the symmetry and provide the necessary 3-dimensional arrangement of the nanoinclusions.
The expected benefits of the program will be both educational and societal. Anticipated research outcomes are an independence from Nature's limited selection of active electromechanical materials and an ability to design multifunctionality by assembling arbitrary non-active material combinations. Apart from resolutions of fundamental scientific questions related to piezoelectricity at the nanoscale, technological applications of the proposed research are anticipated in next generation actuators, sensors, MEMs and NEMs with consequent impact on diverse industries such as, Electronics, Space and Aerospace, Biomedical, Defense among others. The educational impact is that undergraduate and graduate students will be trained in emerging and interdisciplinary scholarly research. Research and education will be integrated by focusing on the education, outreach and recruitment through (1) Undergraduate summer research opportunities, (2) High School outreach using our existing NSF RET, REU and AGEP, and (3) Middle/High School student demonstrations. Research findings will be incorporated into courses, and broadly disseminated through conference presentations, scholarly publications, and the PIs's websites.
The overarching goal of this research is to understand and develop active nanostructured architectures such as nanocomposite skins and films that do not require any piezoelectric materials as constituents and in principle can be designed with any material combination. During the course of this grant, we were able to make several significant advances: (1) We were able to show that unusual materials like graphene nanoribbons, which are non-piezoelectric, can be coaxed in to behaving like piezoelectrics by judiciously exploiting symmetry and flexoelectricity. Significantly, using a combination of experiments and quantum mechanical calculations, we were able to elucidate the fundamental mechanisms underpinning unexpected piezoelectricity in Graphene Nitride. (2) We found that, in soft materials, merely by add small amounts of charge at composites interfaces (electret type configuration) can (in conjunction with flexoelectricity) lead to electromechanical couplings that can be 10 times larger than those of hard materials. (3) We have discovered the magnetization on the dislocation cores of transition metal disulfides, and in particular predicted the possibility of both ferromagnetic and antiferromagnetic ordering. While looking for piezoelectric effects this discovery may prove quite important with possible applications in spintronic devices. More than forty peer-reviewed journal papers have emerged from this effort. As part of the broader impact, we recruited female graduate students, developed short courses on nanotechnology, incorporated the state-of-the-art findings in advanced graduate courses and widely disseminated the results through conference presentations, invited talks and peer-review journal papers. Out reach has involved participation in school camps, training of school students as interns---including from minority communities and establishment of a strong international network relation with Tunisia and Egypt.
