A technique has been developed that allows the application of free-standing membranes of polymer adhesives used in microfabricated structures. The film is made free-standing by the application of the adhesive to a pol...
A technique has been developed that allows the application of free-standing membranes of polymer adhesives used in microfabricated structures. The film is made free-standing by the application of the adhesive to a polymer template, followed by an adhesion step to a microfabricated substrate, and the final release of the film by the removal of the polymer template. It was found that the surface treatment used to treat the Teflon template made it adhere too strongly to the adhesive film for this application. The results show that Gel-Paks make a suitable template for the transference of polymer films over holes of at least micron size.
Summary form only given. We have demonstrated the operation of a high power near diffraction limited external cavity QW laser by implementing a single-angled facet curved input preamplifier with wide tuning and high s...
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Summary form only given. We have demonstrated the operation of a high power near diffraction limited external cavity QW laser by implementing a single-angled facet curved input preamplifier with wide tuning and high spectral purity at both 1.55 and 0.83 /spl mu/m wavelengths.
A research program was initiated with both experimental and computational chemistry based molecular modeling components to investigate specific amino acid-surface interactions. The experimental portion of this study, ...
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Sedimentation is often a problem in electrorheological (ER) fluids featuring solid particles suspended in a low‐density hydrocarbon oil. This problem was addressed by synthesizing particles comprising silica microbal...
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An equation, based on thermodynamic considerations to relate the glass transition temperature, T g , to compositional variation of a polymer system, is adapted in this article for modeling the T g vs. fractional conve...
The isothermal enthalpy changes with time of a dental composite were examined by microcalorimetry to isolate the effects of different filler concentrations and curing times on chemical aging of these composites. Ureth...
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The isothermal enthalpy changes with time of a dental composite were examined by microcalorimetry to isolate the effects of different filler concentrations and curing times on chemical aging of these composites. Urethane dimethacrylate (UDMA) monomer, zirconia-silica (ZS) powder, and 3-methacryloxypropyltrimethoxysilane (MAPM) were used as organic and inorganic matrices, and a coupling agent, respectively. The composite was mixed in different ratios and cured by visible light. The enthalpy changes with time for 0, 15, 45, 75% ZS-filled UDMA and 75% MAPM-silanated ZS-filled UDMA cured for 13, 30, 90, 150, and 300 s were measured at 37.0°, 57.0°, and 65.5°C until equilibrium. Increased curing time and filler concentration caused the excesss enthalpy changes ( dH ) and their rate of change ( dH/dt ) to increase with annealing time and apparent equilibrium was reached faster. In addition, dH showed nonlinear dependence with the increase in filler concentration by showing a maxima for samples containing 25 wt % filler. Further, filler silanation caused dH/dt to increase and required shorter times to reach apparent equilibrium. dH also reached a minimum when samples contained silanated filler, compared to composites containing unsilanated filler. It was concluded that the shorter curing time caused the occurrence of spontaneous densification, which facilitated continual resin curing; and longer curing time caused higher crosslinking of the organic phase. Moderate concentration of inorganic phase restricts the molecular motion of the surface layer of polymer onto filler particles, and the polymer is regarded as highly crosslinked, while a higher filler concentration forms aggregates that are covered by the polymer which causes a decrease in the molecular packing of the resin, and is reflected as low enthalpy values. Finally, silanation of the filler showed a highly endothermic reaction that is probably due to breaking and forming of bonds at the interface between the organ
A localized stress relaxation technique is described suitable for testing miniature structures and components. The actual size of the area that can be tested depends on the size of the indenter and the sensitivity of ...
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A localized stress relaxation technique is described suitable for testing miniature structures and components. The actual size of the area that can be tested depends on the size of the indenter and the sensitivity of the load measurement device. However, the indenter should not be so small that macroscopic theory of deformation cannot be used. The technique described includes a quantitative treatment of the data which can be handled by a computer. Extensive data collection can be made so that many deformation parameters can be examined by using this simple test.
The impression made by a loaded cylindrical flat-end punch on a polymer surface was observed to disappear with time at the same temperature after the load was removed. The depth-time relation appeared to obey second o...
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The impression made by a loaded cylindrical flat-end punch on a polymer surface was observed to disappear with time at the same temperature after the load was removed. The depth-time relation appeared to obey second order kinetics. The temperature dependence of the rate constant shows two consecutive processes with activation energies, 906 kJ/mole (between 143 and 147 degrees C) and 91 kJ/mole (between 150 and 160 degrees C) for PC (Tg is at about 146 degrees C) and 440 kJ/mole (between 104 and 110 degrees C) and 95 kJ/mole (between 115 and 140 degrees C) for PMMA (Tg is at about 112 degrees C). These activation energies are probably associated with the motion and annihilation of conformational or structural defects of opposite signs. This kind of shape memory phenomena may be general for all amorphous polymers.
Intensified plasma-assisted processing (IPAP), is a surface modification technique developed recently in our laboratory. Plasma intensification is accomplished by triode discharge and can be utilized for low-pressure,...
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Intensified plasma-assisted processing (IPAP), is a surface modification technique developed recently in our laboratory. Plasma intensification is accomplished by triode discharge and can be utilized for low-pressure, low-temperature diffusion treatments and synthesis of a range of advanced compounds. The energetic flux of ions and neutrals generated in IPAP can create highly favorable surface conditions producing significant improvements in properties ranging from thermal and chemical stability to wear resistance. The objective of the present study was to investigate further the role of energetic particle bombardment on the modification process. IPAP nitriding experiments were carried out on Ti-6Al-4V substrates at specific nitrogen flux levels and Bur energies. Parallel experiments were performed by low-energy, broad-beam nitrogen implantation at comparable ion energies and dose levels. Nitrogen concentrations and penetration depths were determined by depth profiling using AES and microhardness measurements. The experimental results were used to derive effective nitrogen diffusivities to assess the effect of the energetic particle bombardment on the diffusion process. For both IPAP and ion implantation, nitrogen diffusion into titanium nitride and solid solution layers is greatly accelerated compared to conventional ion nitriding. IPAP is almost as effective as low-energy ion implantation in enhancing nitrogen penetration when the two processes use ions of similar energies and dose levels. The energetic neutrals present in IPAP appear to further enhance the growth of surface nitride layers. Analysis also indicates that an optimal ion energy may exist. (C) 1997 Elsevier science S.A.
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