Materials Literature
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Conditions for preparing samples of Yb<SUP>3+</SUP>-doped fluoroaluminate glasses of high optical quality ((Delta) n <EQ 2 X 10<SUP>-6</SUP>), their structure, and optical properties have been studied while varying the phosphate (5 to 40 mol%) and the Yb<SUP>3+</SUP> content (5 to 12 X 10<SUP>20</SUP> ions/cm<SUP>3</S…
The optical and mechanical properties of polycrystalline MgAl<SUB>2</SUB>O<SUB>4</SUB> spinel make this material of interest for transparent armor and for window and dome applications in the 0.3 micrometers to 5.5 micrometers range. Spinel was briefly produced commercially, and qualified for a range of dome and window…
Linear α,ω-vinyl-terminated poly(diethylsiloxane) (PDES) chains were synthesized and fractionated to obtain melts of low polydispersity. The fractionated samples were characterized using gel permeation chromatography and dilute solution viscometry. PDES elastomers were also prepared from the melts using hydrosilylatio…
Polyethers having well-defined comb-shaped architectures were prepared by using poly(4-hydroxystyrene) (PHSt) as a multifunctional initiator for graft polymerization of either ethylene oxide (EO) or a mixture of EO and propylene oxide (PO). The grafting process was performed in 1,4-dioxane using NaH as ionizer for the…
The field of molecule-based magnets is a relatively new branch of chemistry, which involves the design and study of molecular compounds that exhibit a spontaneous magnetic ordering below a critical temperature, Tc. One major goal involves the design of materials with tuneable Tc's for specific applications in memory s…
Summary Solid state NMR spectroscopy has been used in this work to investigate crystallinity of cellulose in spruce wood before and after kraft pulping and TCF bleaching. Effects of refining of the spruce kraft pulp in water and in weak alkali have been studied by determination of the crystallinity of isolated fines a…
Highly textured semicrystalline poly(ethylene terephthalate) (PET) prepared through an equal channel angular extrusion (ECAE) process was studied using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), optical microscopy (OM), differential scanning calorimetry (DSC), and annealing tests. OM…
Recently, the U.S. Army Research Laboratory (ARL) has focused increased attention on the development of transparent armor material systems for a variety of applications. Future combat and non-combat environments will require lightweight, threat adjustable, multifunctional, and affordable armor. Current glass/polycarbo…
Results of stress−strain, infrared dichroism, and birefringence experiments on silica-filled poly(dimethylsiloxane) networks show strong upturns of the stress with increasing deformation while segmental-orientation-strain relations remain linear over the same deformation range. As a result of this difference, the stre…
Atomic force microscopy (AFM) has been used to study tethered polystyrene - b -poly(methyl methacrylate) (PS - b -PMMA) and polystyrene - b -poly(methyl acrylate) (PS - b -PMA) brushes on flat substrates. The PS - b -PMMA surface was smooth after treatment with CH 2 Cl 2; treatment with cyclohexane led to a relatively…
Surface-immobilized polystyrene- b -polyacrylate brushes have been synthesized on silicate substrates from chlorine-terminated polystyrene (PS) brushes by atom transfer radical polymerization (ATRP). ATRP of methyl methacrylate (MMA), methyl acrylate (MA), and ( N,N -dimethylamino)ethyl methacrylate (DMAEMA) produced…
Due to particle conservation, Canonical Molecular Dynamics (MD) simulations fail in the description of surface phase transitions involving coverage or lateral density changes. However, a step on the surface can act effectively as a source or a sink of atoms, in the simulation as well as in real life. A single surface…
The effect of surface curvature on the law relating frictional forces F with normal load L is investigated by molecular dynamics simulations as a function of surface symmetry, adhesion, and contamination. Curved, non-adhering, dry, commensurate surfaces show a linear dependency, F proportional to L, similar to dry fla…
Master plot methods based on the integral and/or the differential forms of the kinetic equation describing solid-state reactions have been redefined by using the concept of the generalized time, θ, introduced by Ozawa. This redefinition permits the application of these master plots to the kinetic analysis of solid-sta…
The purpose of this study was to understand the relationship between the mechanism of interdiffusion of the polymer chains across the interface and the formation of crosslinks in the interfacial zone when two elastomer sheets are joined and crosslinked. It is commonly accepted that the strength of the interface thus o…
Theory suggests that the otherwise rapid folding of simple heteropolymer models becomes "glassy"-dominated by multiple kinetically trapped misfolded states-at low temperatures or when the overall bias toward the native state is reduced relative to the depth of local minima. Experimental observations of nonsingle-expon…
The described study concentrated on the investigation of II-VI semiconductor quantum dots, prepared as colloidal species imbedded in phosphate glass, or chemically deposited on a substrate. The ultimate goal of the present research was concerned with the examination of the influence of the surface/interface quality on…
A family of graft copolymers that can sterically inhibit interactions between biological surfaces was developed. These copolymers contained phenylboronic acid (PBA) groups as saccharide-binding moieties on a poly-(L-lysine) backbone and poly(ethylene glycol) (PEG) grafted as adhesion-resisting side chains. These copol…
We describe two efficient methods of estimating the fluid permeability of standard models of porous media by using the statistics of continuous Brownian motion paths that initiate outside a sample and terminate on contacting the porous sample. The first method associates the "penetration depth" with a specific propert…
Cd2Os2O7 crystallizes in the pyrochlore structure and undergoes a metal-insulator transition (MIT) near 226 K. We have characterized the MIT in Cd2Os2O7 using X-ray diffraction, resistivity at ambient and high pressure, specific heat, magnetization, thermopower, Hall coefficient, and thermal conductivity. Both single…