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Title: Polymorphic Peptide Hair Project

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Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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DOE Contract Number:
Resource Type:
Technical Report
Country of Publication:
United States

Citation Formats

Parker, G J, Anex, D S, Leppert, M F, Baird, L, Matsunami, N, and Leppert, T. Polymorphic Peptide Hair Project. United States: N. p., 2014. Web. doi:10.2172/1130556.
Parker, G J, Anex, D S, Leppert, M F, Baird, L, Matsunami, N, & Leppert, T. Polymorphic Peptide Hair Project. United States. doi:10.2172/1130556.
Parker, G J, Anex, D S, Leppert, M F, Baird, L, Matsunami, N, and Leppert, T. 2014. "Polymorphic Peptide Hair Project". United States. doi:10.2172/1130556.
title = {Polymorphic Peptide Hair Project},
author = {Parker, G J and Anex, D S and Leppert, M F and Baird, L and Matsunami, N and Leppert, T},
abstractNote = {},
doi = {10.2172/1130556},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2014,
month = 4

Technical Report:

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  • Carbon nanotubes (CNT) are unique nanoscale building blocks for a variety of materials and applications, from nanocomposites, sensors and molecular electronics to drug and vaccine delivery. An important step towards realizing these applications is the ability to controllably self-assemble the nanotubes into larger structures. Recently, amphiphilic peptide helices have been shown to bind to carbon nanotubes and thus solubilize them in water. Furthermore, the peptides then facilitate the assembly of the peptide-wrapped nanotubes into supramolecular, well-aligned fibers. We investigate the role that molecular modeling can play in elucidating the interactions between the peptides and the carbon nanotubes in aqueous solution.more » Using ab initio methods, we have studied the interactions between water and CNTs. Classical simulations can be used on larger length scales. However, it is difficult to sample in atomistic detail large biomolecules such as the amphiphilic peptide of interest here. Thus, we have explored both new sampling methods using configurational-bias Monte Carlo simulations, and also coarse-grained models for peptides described in the literature. An improved capability to model these inorganichiopolymer interfaces could be used to generate improved understanding of peptide-nanotube self-assembly, eventually leading to the engineering of new peptides for specific self-assembly goals.« less
  • A theory describing the polymorphism induced by shock waves in silicates, oxides, sulfides, and many inorganic solids is presented. Shock wave experiments conducted on these and other materials indicate that many transformations to high-pressure phases are triggered via the production of shear bands and, in some cases, formation of high-density amorphous phases. Shock states in the mixed phase regimes, of quartz, carbon, and boron nitride, are quantitatively described in terms of the properties of both their low- and high-pressure phases. Good agreement between the calculated results and measured Hugoniot data in the mixed phase regime is obtained. By fitting themore » pressures of the onset of the phase transition from graphite to diamond, and associating its triggering with crossing the extension of the metastable melting line of graphite, we obtain a similar shaped curve to the metastable melting line obtained by Bundy. Similarly, the transition from quartz to stishovite is associated with the metastable melting line of coesite. The present theory, when fit to the onset of the mixed phase regime of graphite like boron nitride transforming to cubic boron nitride Hugoniot, predicts the standard entropy for cubic BN to be 0.4-0.5 J/g K.« less
  • Hydrostatic and constant-stress-difference (CSD) experiments were conducted at RT on 3 different sintering runs of unpoled, Nb-doped lead-zirconate-titanate ceramic (PZT 95/5-2Nb) in order to quantify influence of shear stress on displacive, martensitic-like, first-order, rhombohedral [r arrow] orthorhombic phase transformation. In hydrostatic compression at RT, the transformation began at about 260 MPa, and was usually incompletely reversed upon return to ambient. Strains associated with the transformation were isotropic, both on first and subsequent hydrostatic cycles. Results for CSD tests were quite different. First, the confining pressure and mean stress at which the transition begins decreased linearly with increasing stress difference. Second,more » the rate of transformation decreased with increasing shear stress and the accompanying purely elastic shear strain. This contrasts with the typical observation that shear stresses increase reaction and transformation kinetics. Third, strain was not isotropic during the transformation: axial strains were greater and lateral strains smaller than for the hydrostatic case, though volumetric strain behavior was comparable for the two types of tests. However, this effect does not appear to be an example of true transformational plasticity: no additional unexpected strains accumulated during subsequent cycles through transition under nonhydrostatic loading. If subsequent hydrostatic cycles were performed on samples previously run under CSD conditions, strain anisotropy was again observed, indicating that the earlier superimposed shear stress produced a permanent mechanical anisotropy in the material. The mechanical anisotropy probably results from a one-time'' crystallographic preferred orientation that developed during the transformation under shear stress. Finally, in a few specimens from one particular sintering run, sporadic evidence for a shape memory effect'' was observed.« less
  • The factors which affect the transformation of amorphous alumina to crystalline alumina in the temperature range 350 to 650/sup 0/C were studied. Amorphous alumina, with small amounts of added impurities, was heated in an atmosphere containing the oxides of nitrogen, air, and water vapor, and the amount of crystalline alumina was determined. Alpha alumina was the predominant crystalline form after heating amorphous alumina that was prepared in a fluid bed calciner. The effects of temperature, composition of the atmosphere, time of heating, impurities, and method of preparation of the amorphous alumina on the transformation to crystalline phases were investigated. Anmore » atmosphere containing water vapor and the oxides of nitrogen and a small amount of sodium nitrate in the alumina product were necessary to produce the alpha alumina phase from amorphous alumina at the relatively low temperature of 400/sup 0/C. Boric acid added to the fluid-bed calciner feed successfully inhibited the formation of the alpha crystalline form.« less
  • Some time ago we presented evidence that, under nonhydrostatic loading, the F{sub R1} {r_arrow} A{sub O} polymorphic phase transformation in unpoled PZT 95/5-2Nb ceramic began when the maximum compressive stress equaled the hydrostatic pressure at which the transformation otherwise took place. More recently, we showed that this simple stress criterion did not apply to nonhydrostatically compressed, poled ceramic. However, unpoled ceramic is isotropic, whereas poled ceramic has a preferred crystallographic orientation and is mechanically anisotropic. If we further assume that the transformation depends not only on the magnitude of the compressive stress, but also its orientation relative to some feature(s)more » of PZT 95/5-2Nb's crystallography, then these disparate results can be qualitatively resolved. In this report, we first summarize the existing results for unpoled and poled ceramic. Using our orientation-dependent hypothesis and these results, we derive simple arithmetic expressions that accurately describe our previously-observed effects of nonhydrostatic stress on the transformation of unpoled ceramic. We then go on to test new predictions based on the orientation-dependent model. It has long been known that the transformation can be triggered in uniaxial compression: the model specifically requires a steadily increasing axial stress to drive the transformation of a randomly-oriented polycrystal to completion. We show that when the stress is held constant during uniaxial compression experiments, the transformation stops, supporting our hypothesis. We close with a discussion of implications of our model, and ways to test it using poled ceramic.« less