Effect of ionic content,solid content,degree of neutralization,and chain extension on aqueous polyurethane dispersions prepared by prepolymer method

There are many variables in the preparation of aqueous polyurethane (PU) dispersions. Carboxylic acid content, solid content, degree of pre/postneutralization of the carboxylic acids, and chain extension all impact dispersion particle size, viscosity, pH, molecular weights, and glass transition temperature. This study evaluated the impact of these variables on a given PU dispersion formulation prepared from isophorone diisocyanate, an aliphatic polyester polyol, dimethylol propionic acid, and hexamethylene diamine with triethyl amine as the neutralizing base and N‐methyl pyrrolidone as the cosolvent. Changes in carboxylic acid content, degree of preneutralization, and chain extension were found to have the expected impacts on dispersions properties. Increased ionic content in the dispersion step led to lower particle size and higher viscosity, increased chain extension with its concurrent increase in molecular improved subsequent film properties. Surprising results were obtained by varying the amount of postneutralization and from increased solids content at the time of dispersion. Unexpectedly, both of these variations led to much higher dispersion viscosities and particle size in solution. To have these changes take place, it is theorized that there is a major change in solution morphology caused by these modifications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2514–2520, 2005     

Outcome of rheumatoid arthritis and psoriasis following autologous stem cell transplantation for hematologic malignancy

Based on successful results in animal models, it has been proposed that high-dose myeloablative therapy followed by autologous bone marrow or stem cell transplantation (ABMT/ASCT) may cure autoimmune disease. The coexistence of autoimmune disease and hematologic malignancy provides an opportunity to examine the response of autoimmune disease to ABMT or ASCT. We describe 4 patients with autoimmune disease (3 with psoriasis and 1 with rheumatoid arthritis) and hematologic malignancy. In each patient, the autoimmune disease remitted posttransplantation, but, in 4 patients with long-term followup, it recurred at 8-24 months. The earliest relapse occurred in a patient treated with interferon-alpha. Our experience suggests that a single autograft with unpurged stem cells is unlikely to cure autoimmune disease, but that other strategies building on this approach are worthy of investigation.     

Effects of three crosslinkers on colored pH‐responsive core–shell latexes

Environmentally responsive hydrogels have become attractive research subjects for many applications. In this work, a series of pH‐sensitive and color‐changing nanoparticles (nanogels) with core–shell structures were synthesized. The cores were blue latex particles synthesized by a miniemulsion technique with styrene and methacrylic acid as monomers and Neozapon Blue 807 as a dye. The shell was a pH‐sensitive polymer that was precipitation‐polymerized onto the core from 2‐(diethylamino) ethyl methacrylate with N,N′‐methylenebisacrylamide, poly(propylene glycol) diacrylate, and divinylbenzene as crosslinking agents. In the resultant latexes, the color was observed to change from deep blue to pale blue as the pH of the system was changed from a high of 10 to a low of 3. The synthesized latexes and particles (gels) were then characterized with an ultraviolet–visible spectrometer, dynamic light scattering, Fourier transform infrared, and nuclear magnetic resonance. Atomic force microscopy was also used to investigate the different morphologies of the particles after the synthesized latexes were dried at different pH values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tilted superlattice composition profile determined by photoluminescence and thermal disordering

The composition profile of an (AlAs)_1/2(GaAs)_1/2 tilted superlattice is characterized for the first time. The tilted superlattice sample is thermally disordered, and the energy of the direct band gap photoluminescence peak is measured as a function of increasing layer interdiffusion. The shift in the photoluminescence peak energy after completely disordering the tilted superlattice is 39 meV. A theoretical model is used to simulate the change in band gap as a function of layer interdiffusion for several composition profiles. The profile that gives the best fit to the experimental data is chosen. The tilted superlattice composition profile is found to be sinusoidal, varying from Al_0.40Ga_0.60As to Al_0.60Ga_0.40As.     

Photoconductivity in p-i-n Quantum Well Optical Modulators

Abstract

We have studied the temperature dependence of the current due to photoexcited carriers in p-i-n single quantum-well optical modulators, in order to ascertain the dominant transport mechanisms involved. A model describing the photocurrent is presented which includes the temperature and field dependence of the thermal emission, the tunnelling, the mobility and the recombination rate. A comparison between the experimental results and the model is also presented, outlining the probable transport processes.     

Optical quality GaInAs grown by molecular beam epitaxy

Ga₄₇In₅₃As films have been grown by molecular beam epitaxy (MBE) on InP substrates. The unintentionally doped material has a free electron concentration of 8 × 10¹⁵cm^-3 and exhibits sharp (~5 meV linewidth) exciton recombination in the 4K photoluminescence. The films were grown on (100) InP surfaces which were thermally cleaned in the arsenic beam. The effects of the substrate temperature during growth, the Ga to In flux ratio and the group V to group III flux ratio on the 4K photoluminescence are reported.     

Newly UV-curable polyurethane coatings prepared by multifunctional thiol- and ene-terminated polyurethane aqueous dispersions: Photopolymerization properties

A novel approach toward the preparation of newly UV-curable polyurethane coatings composed of multifunctional thiol- and ene-terminated polyurethane aqueous dispersions is presented. By a synergistic combination of polyurethane dispersions synthesis and thiol-ene chemistry, strategies for the preparation of newly UV-curable polyurethane coatings are developed. Photo-DSC, real-time FTIR, DMA and tensile tests measurements are used to investigate the photopolymerization and mechanical behaviors of newly UV-curable polyurethane coatings. The newly polyurethane coatings have 1.5 times higher polymerization rate and final 99% functional groups conversion in air conditions compared to current urethane-acrylate based UV-curable polyurethane dispersions coatings. UV-cured polyurethane films prepared by this method are also found to exhibit increase in Young's modulus and tensile strength at break by 25% and 10%, respectively. These experiment facts suggest that the incorporation of thiol-ene chemistry to the polyurethane dispersion coatings increase their polymerization rate, producing a high degree of cross-linking. This confirms the preparation of the targeted novel UV-curable polyurethane coatings and reveals the dramatic effect that changes in incorporation of thiol-ene chemistry can have on the photopolymerization behaviors of UV-curable polyurethane dispersions coatings systems.     

Financial Analysis of Large Versus Small Nuclear Power Plants

There have been no new orders for nuclear plants and many nuclear plants under construction have been cancelled in recent years in the United States. Financing problems have been a major factor in this slow down of new nuclear plant activity. Meanwhile, the nuclear plants that have been completed have been operating cost effectively and vielding fossil fuel conservation and air quality bene fits. Smaller plants have been designed in the past for the purpose of penetrating markets in developing countries and countries with relatively small utility systems. This paper examines the question of whether these smaller plants would be a viable option to large nuclear plants in the United States. Although the smaller plants are estimated to have a somewhat higher capital cost on a $/kW basis, they have the potential advantage of a lower total financial commitment. The computational tools required for this evaluation are optimal generation planning and financial simulation programs and the corresponding generation and financial data bases for a variety of systems. The results of this evaluation show that on large electric systems with large growth rates the financing benefit from small nuclear plants is minimal while on small systems with small growth rates, the potential financing benefits from small nuclear plants can be substantial.     

Sheet electron concentration at the heterointerface in Al0.48In0.52As/Ga0.47In0.53As modulation-doped structures

Sheet electron concentration at the heterointerface in Al0.48In0.52As/Ga0.47In0.53As modulation-doped structures has been calculated as a function of the spacer layer thickness, the doping concentration in Al0.48In0.52As and the lattice temperature. The calculated results were compared with those for Al0.3Ga0.7As/GaAs structures and also with the experimental data. It is shown that, compared with AlGaAs/GaAs about 1.5 times higher sheet electron concentration can be obtained in AlInAs/GaInAs at the same doping level, which is in good agreement with the experimental results.