Philip Bradford

Energy storage devices that could be charged and discharged in minutes or seconds while providing high energy densities are necessary for next generation portable electronics, electric vehicles, and in smart grid applications. The proposed research will lead to design rules for controllable, scalable, and customizable manufacturing of a new class of electrode architectures for energy storage based on low density, electrically conductive carbon nanotube foam scaffolds that are hybridized with metal oxides. The research will support the education and training of undergraduate and graduate students on battery material synthesis, electrode manufacturing, device fabrication, and materials characterization.

This proposal addresses the high efficiency generation of acoustic modes in and low attenuation propagation through optical fibers. Applying the proposed sensor technology to structural health monitoring of large structures introduces the multiple challenges of adequately covering surface areas of complex structures, adapting to changes in the structure over the lifetime of the structure, and providing localized, high-resolution imaging of structural defects in regions not necessarily known a-priori.

This project will allow the PhD student, Ms. Enab, to study at NC State during the course of her PhD program in the lab of Dr. Philip Bradford. She will conduct research on advanced textiles enabled by carbon nanotubes.

The PI??????????????????s are to produce CNT arrays and diamond arrays for the potential use in contact free current transfer for homopolar motors. The goal is to provide samples of both type of arrays for testing for their field emission properties. When a suitable growth configuration is established, the NC State team will work to produce electrodes in the shapes required by AML and Eagle Power for their generators.

The development of low density materials is of critical importance to next generation Air Force structures and technologies. The overarching objective of this work is to extend the state of the art in ultra low density materials and develop fundamental understanding of how the structural parameters of cellular materials based on interconnected nanotubes define their mechanical, electrical, thermal properties as well as their surface functionality.

Thermally conductive materials are often used in strategic ways to maximize the temperature differential across thermoelectric energy generators (TEGs) through heat spreaders and heat sinks. Those features are typically made of thermally conductive metals or graphite which are solid and either rigid or semi-flexible depending on the material thickness. To provide the highest ratio of power output to user comfort, ideally TEGs worn on the body should be both flexible and breathable. Flexibility is important for conformability of the device to the body??????????????????s contours and durability during body movement. Breathability is important for long term comfort and opens up the possibility of covering a larger surface area of the skin for power generation. This Seed Project aims to support the ASSIST Self-Powered and Adaptive Low Power Platform, and in particular, the efforts to develop next generation TEG devices that are fully flexible and breathable. This will be accomplished through the study and development of textile based heat spreaders and heat sinks which are made up either ultra-high aspect ratio carbon nanotubes (CNTs) and/or highly graphitic carbon fibers. These highly thermally conductive materials will be hybridized with a small fraction of a polymer component in such a way to retain porosity but encapsulate the fibers and retain the desired morphology.

Aligned CNT sheets will be utilized to produce heaters Phase 1. Due to the very thin structure of the CNT sheets, it is projected that the final thickness of the heater blankets will be no greater than 0.5 mm. Heaters of size up to 15"x15" will be produced for the sponsor in different configurations. At the same time NC State will work to develop methods for the scale up of the process which would occur in Phase II.

SCEYE S.A. is currently funding (Reference Number 2015-0996) our team to pursue research that deals with a fundamental study to develop high performance inflatable laminated envelope fabrics for high altitude airship. The envelope fabric is characterized by its high strength to weight ratio, low helium and hydrogen permeability and UV resistance. SCEYE S.A. is also funding other researchers to develop lightweight and efficient airship components such as batteries, solar cells, and engine. The Company??????????????????s ultimate target is to construct airships with the highest performance with the minimum number of seams across the envelope fabric to dramatically reduce the overall weight of the airship since the inflatable laminated envelope fabric and its seams accounts for the majority of the overall weight of the airship. The current funded project expands over one year (January-December 2015). In this work, small size laminated envelope fabrics are being produced. The constituents of the fabric include high performance fiber reinforced layer laminated with flexible polymer matrix to make the fabric helium/hydrogen tight, surface layer with UV blocking materials, and a layer of carbon nanotube that is infused in the polymer matrix for reinforcement and further UV blocking. This proposal is written in response of solicitation from SCEYE S.A. to conduct a feasibility study on the development of full scale inflatable laminated envelope fabric with zero or minimum seam for the aforementioned airships. The main goal of the proposed research is to conduct a feasibility study on the development of full scale laminated envelope fabric with zero or minimum number of seams for high altitude stratosphere non-rigid airship for long duration and multiple flights.

Aligned CNT sheets will be utilized to produce a heating blanket structure for Phase 1. Due to the very thin structure of the CNT sheets it is projected that the final thickness of the heater blankets will be no greater than 1 mm. Two major approaches will be implemented to determine and their properties and potential for scaling up to large scale blankets. The first approach will use dry wound CNT sheets and will be fabricated and sandwiched in between high temperature films (polyimides or silicones) that have high strength adhesive backing. The second approach would be to wind the CNT sheets and incorporate a heat cured silicone matrix into the sheets before winding. The uncured composite would then be incapsulated in a thin layer of liquid silicone in a molding process to create the electrical insulation of the blanket. The unreacted silicone in the CNT sheets would bond to the encapsulating layers to make a unified blanket with robust integration of the CNT sheets. The procedures for making both types of blankets is relatively simple. Most of NC State's time during Phase I will be spent understanding the configuration of electrical connections to the encapsulated CNT sheets, to tune the properties of the blankets based on the number of CNT layers in the devices and to determine the overall device heating performance. Multiple small devices of dimensions of approximately 6"x2" will be produced to develop the fabrication technique and understand the electrical characteristics. At least two large blankets of 15" x 15" will be provided to Luna for them to demonstrate the out-of-autoclave curing of composites for Phase I.

Viscoelastic polymer foams typically behave in one of two ways. Resilient foams, when compressed, dissipate some of the energy and then can return to their original dimensions. This factor is important for repeat impact events and overall comfort. However, resilient foams have lower mechanical strength, so the amount of energy absorbed is low. Rigid polymer foams are below their glass transition temperature and so impact events tend to crush the cell wall structure allowing for higher strength and energy absorption. These materials must be replaced after each impact event. Polymer foams also exhibit temperature dependent behavior, so a polymer foam optimized for a hot environment may not perform as designed in a cold environment and vice versa. An ideal foam structure for energy absorption applications would have recovery after impact and have temperature independent mechanical properties. This type of foam structure has been demonstrated, in small scale, by the proposer through the use of 3D foam- like assemblies of carbon nanotubes (CNTs). These 3D foam like CNT assemblies will be the basis for new CNT/polymer composite foams which have low density, high compressibility, thermal stability, high energy absorption capability, high level of recoverability and high compressive strength.