Browsing by Author "Carey, Brent J."

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    Dynamic Self-Stiffening in Liquid Crystal Elastomers
    (Nature Publishing Group, 2013) Agrawal, Aditya; Chipara, Alin C.; Shamoo, Yousif; Patra, Prabir K.; Carey, Brent J.; Ajayan, Pulickel M.; Chapman, Walter G.; Verduzco, Rafael
    Biological tissues have the remarkable ability to remodel and repair in response to disease, injury and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials that respond to external stresses through a permanent increase in stiffness are uncommon. Here we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a mobile nematic director, which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement.
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    NASA's Relationship with Nanotechnology: Past, Present, and Future Challenges
    (James A. Baker III Institute for Public Policy, 2012) Matthews, Kirstin R.W.; Carey, Brent J.; Evans, Kenneth M.; Moloney, Padraig G.; Baker Institute Science and Technology Policy Program
    This report reviews the history of nanotechnology research and development at NASA over the past 15 years. Nanotechnology is used to illustrate how NASA has guided new technology development at its own research facilities and through collaborations with university scientists and laboratories. We demonstrate that nanotechnology is representative of NASA's long struggle to translate research projects into viable technologies.
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    Tailoring vertically-aligned carbon nanotube growth for poly(dimethylsiloxane)-infiltrated nanocomposites
    (2010) Carey, Brent J.; Ajayan, Pulickel M.
    This thesis discusses the viability of the polymer infiltration nanocomposite preparation technique for aligned carbon nanotubes (A-CNTs) as produced by two methods: pre-deposited catalyst chemical vapor deposition (CVD), and vapor-phase CVD. Both types of growth furnaces were constructed, and the resultant A-CNT "forests" were impregnated with poly(dimethylsiloxane), a highly-compliant silicone elastomer. The survivability of the CNT alignment subsequent to the polymer infiltration was studied for the respective nanocomposites, and it was observed that the thin-walled CNTs produced by the pre-deposited catalyst CVD method were not robust enough to maintain alignment during the infiltration, in contrast to the thicker-walled vapor-phase-grown CNTs. The dynamic mechanical properties of the successfully-impregnated composites were then studied, and their strain- and frequency-dependent behavior was probed both transverse and longitudinal to the alignment direction of the CNTs, revealing distinct responses due to their anisotropy.