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Aberdeen Proving Ground, MD, United States

Zander N.E.,U.S. Army | Dong H.,U.S. Army | Dong H.,Bowhead Science and Technology LLC | Steele J.,U.S. Army | Grant J.T.,University of Dayton
ACS Applied Materials and Interfaces

The use of cellulose materials for biomedical applications is attractive due to their low cost, biocompatibility, and biodegradability. Specific processing of cellulose to yield nanofibrils further improves mechanical properties and suitability as a tissue engineering substrate due to the similarity to the fibrous structure, porosity, and size-scale of the native extracellular matrix. In order to generate the substrate, nanocellulose hydrogels were fabricated from carboxylated cellulose nanofibrils via hydrogelation using metal salts. Hydrogels cross-linked with Ca2+ and Fe3+ were investigated as tissue culture substrates for C3H10T1/2 fibroblast cells. Control substrates as well as those with physically adsorbed and covalently attached fibronectin protein were evaluated with X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and enzyme linked immunosorbent assay (ELISA). Significantly more cells were attached to surfaces modified with protein, with the highest number of cells adhered to the calcium cross-linked hydrogels with covalently attached protein. © 2014 American Chemical Society. Source

Martin J.,U.S. Army | Martin J.,University of Delaware | Hirsch S.G.,U.S. Army | Giri A.,U.S. Army | And 3 more authors.
Proceedings of the IEEE Conference on Nanotechnology

Highly-ordered, densely-packed, hexagonal TiO2 nanotubes were synthesized in a single-step anodization of Ti foil using a constant dc potential of 60 V. The synthesized nanotubes exhibit a bamboo-like structure, with rings formed along the length. X-ray diffraction reveals the as-grown nanotubes to be amorphous, which upon annealing at 723 K changes to a dominantly crystalline anatase phase. A high concentration of the electrolyte coupled with a mechanically uneven Ti surface leads to nano-grass like structure. A long anodization time also contributes to rapid breakdown of the Nanotubes. © 2012 IEEE. Source

Parsons P.,U.S. Army | Parsons P.,University of Delaware | Duncan K.,U.S. Army | Giri A.K.,U.S. Army | And 3 more authors.
Journal of Applied Physics

The magnetic properties of polycrystalline NiZn ferrite nanoparticles synthesized using a polyol-reduction and coprecipitation reaction methods have been investigated. The effects on magnetization of synthesis approach, chemical composition, processing conditions, and on the size of nanoparticles on magnetization have been investigated. The measured room-temperature magnetization for the as-prepared magnetic nanoparticles (MNP) synthesized via polyol-reduction and coprecipitation is 69Am2kg-1 and 14Am2kg-1, respectively. X-ray diffraction measurements confirm spinel structure of the particles with an estimated grain size of ∼80nm obtained from the polyol-reduction and 28nm obtained from these coprecipitation techniques. Upon calcination under atmospheric conditions at different temperatures between 800°C and 1000°C, the magnetization, M, of the coprecipitated MNP increases to 76Am2kg-1 with an estimated grain size of 90nm. The MNP-polymer nanocomposites made from the synthesized MNP in various loading fraction and high density polyethylene exhibit interesting electromagnetic properties. The measured permeability and permittivity of the magnetic nanoparticle-polymer nanocomposites increases with the loading fractions of the magnetic nanoparticles, suggesting control for impedance matching for antenna applications. © 2014 U.S. Government. Source

Ballard Jr. J.R.,U.S. Army | Howington S.E.,U.S. Army | Wilhelms S.C.,Bowhead Science and Technology LLC
IEEE Geoscience and Remote Sensing Letters

The long-wave infrared reflectance of in situ disturbed and undisturbed soils will often have distinct spectral characteristics that are dependent on the soil's physical and spectral constitutive properties. This study examines how rainfall alters the measured directional-hemispherical thermal infrared (8-14 μm ) spectral reflectance of a disturbed soil with a specified sand/silt ratio using a calibrated rainfall simulator. For an accumulated rainfall of 8.0 cm, the mean disturbed soil thermal infrared spectral reflectance within 8.1-9.2-μm waveband increases from an initial reflectance of 13% to a maximum reflectance of 31%. Sixty percent of this reflectance change occurred with only 1.0-cm accumulated rainfall. This study shows that, for this described disturbed sand/silt soil mixture, small accumulated rainfall amounts significantly alter the directional-hemispherical thermal infrared spectral reflectance. © 2004-2012 IEEE. Source

Sliozberg Y.R.,U.S. Army | Sliozberg Y.R.,Bowhead Science and Technology LLC | Mrozek R.A.,U.S. Army | Schieber J.D.,Illinois Institute of Technology | And 3 more authors.
Polymer (United Kingdom)

Polymer gels are composed of a chemically or physically cross-linked polymer that is highly swollen with solvent. Two important limitations for the practical application of polymer gels are low toughness and a limited ability to tailor the strain-rate dependent mechanical response. Both these limitations are due to the high loadings of small molecule solvents that are typically incorporated into the gel formulation. Here, we provide insight into the role of physical entanglements on the performance of polymer gels, when the solvent molecular weight is large enough to entangle with the polymer network. Our simulations demonstrate that the solvent entanglements dominate the time-dependent elastic modulus of polymer gels with high-molecular-weight solvent. We have found that entanglement contribution to the modulus is essentially equal for the entangled polymer melt and loosely cross-linked entangled polymer gel at high strain rate. At lower strain rate, the modulus of the polymer gels develops a long-lived plateau that originates from "semi-trapped" entanglements formed between network strands and polymer solvent. The simulations were validated with selected experiments of chemically cross-linked polydimethylsiloxane (PDMS) elastomers loaded with a non-reactive silicone oil solvent, where the solvent molecular weight was varied. The simulations and experimental results demonstrate that highly entangled solvent can be used to tune the rate dependent modulus of polymer gels. © 2013 Elsevier Ltd. All rights reserved. Source

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