Role of network nematicity in swelling and phase equilibria of polymer networks in nematic solvents

Swelling and phase equilibria of polymer networks in a low molecular mass liquid crystal (LC) have been investigated as a function of network nematicity. LC networks with varying nematicity were prepared by copolymerization of mixtures of mesogenic monomers and non-mesomorphic (styrene) monomers with various compositions. Molar fraction of mesogenic monomer (x) in copolymer network strongly influences the swelling behavior as well as the nematic-isotropic (N-I) transitions in both dry and swollen states. The swollen networks of sufficiently high x with strong nematicity exhibit a sharp N-I transition and simultaneously undergo a discontinuous change in gel volume, i.e. volume phase transition. Meanwhile, the swollen networks of x≤0.8 with less nematicity show a broad N-I transition, and the resulting volume change proceeds continuously over a finite temperature range. When x decreases further down to less than 0.5, the nematicity of the dry networks vanishes. The nematic ordering in the swollen copolymer networks of x<0.5 occurs at the same temperature as the N-I transition temperature of the pure nematic solvent (T_NI^S), which yields the inflection in the swelling-temperature curve. A mean field theory considering network nematicity as a variable describes the effects of x on volume phase transition such as a shift of T_NI^G and a change in the magnitude of volume transition, apart from the emergence of continuous volume transition due to the broad N-I transition. The purely isotropic network of x=0 appreciably swells in the nematic solvent. The solvent inside the gel forms the nematic phase at the temperatures below which conflicts with the classical theoretical prediction that nematic ordering of LC solvent in fully swollen isotropic network never occurs.     

Hydrogenation of nitro compounds with supported platinum catalyst in supercritical carbon dioxide

Hydrogenation of a series of substituted nitro compounds such as 2-,3-,4-nitroanisole, 2-,3-,4-nitrotoluene, 2,4-dinitrobenzene and 2,4-dinitrotoluene has been studied in supercritical carbon dioxide, scCO₂ (two phases), and ethanol (three phases) with a 5 wt.% carbon supported platinum catalyst. The solubility of these compounds in scCO₂ has also been examined in the presence and absence of hydrogen. The solubility of those nitro compounds increases with increasing CO₂ pressure but decreases with the presence of hydrogen. The solubility is in the order of nitrotoluene > nitroanisole > dinitrotoluene, dinitrobenzene. Although the total conversion obtained with hydrogenation in scCO₂ is similar to that in ethanol, the selectivity to amino products is higher in the former reaction medium, indicating that scCO₂ is an ideal medium for the production of amino compounds with hydrogenation of nitro substrates using conventional supported metal catalysts.     

Morphology development of 10‐μm scale polymer particles prepared by SPG emulsification and suspension polymerization

Classicalparticle morphologies, core‐shell, hemisphere, sandwich, and so on, were all reproducible by starting from ca. 10‐μm uniform droplets composed of monomers, initiator, solvents, and polymer, and polymerizing them by subsequent suspension polymerization. SPG (Shirasu porous glass) membrane was employed to form uniform size droplets having the coefficient of variation (CV) around 10%. Styrene (ST) and acrylic monomers were used as monomers, and their polymers were dissolved in the droplets to investigate the development of phase separation. When hydrophilic methyl methacrylate (MMA) was polymerized in the droplets with a mixed solvent consisting of hydrophilic hexanol (HA) and hydrophobic benzene and hexadecane (HD), the resulting morphology shifted from hemisphere to sandwich and eventually to PMMA/solvent core‐shell with increasing hydrophilicity of the mixed solvent. The sandwich was converted to the core‐shell after several weeks elapsed. As styrene was added to MMA, the morphology shifted from hemisphere core/solvent shell to raspberry core/solvent shell as the fraction of ST increased. The domain of the mixed solvent in the raspberry core was reduced with increasing the hydrophilicity of the mixed solvent. All these morphologies were eventually converted to the copolymer core/solvent shell. When a mixed monomer of styrene and MMA dissolving polystyrene (PS) was polymerized, the resulting morphology shifted from salami to core‐shell with increasing the MMA fraction in the comonomer. The salami particles were then swollen with toluene, and after the swelling, toluene was removed under the different temperature and pressure. The final particle morphology converted to the core‐shell with a milder rate of toluene removal which was predicted from the thermodynamic model. When styrene and cyclohexyl acrylate (CHA), a pair with widely different reactivity ratios, were copolymerized, salami morphologies, with tiny CHA‐rich domains dispersed in the matrix, were obtained even at a higher fraction of CHA in comonomer. Effects of glass transition temperature of the polymers, molecular weight, and the composition of copolymers were taken in consideration whenever the final morphologies were discussed. By these experiments, the authors tried to demonstrate an advantage of using large uniform spheres for the particle morphology studies. SPG emulsification technique was a potential tool because of its free formulation of the droplets, and the subsequent polymerization could undergo without the breakup or coalescence of the droplets. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2200–2220, 2001     

Absorption of metal cations by modified B. mori silk and preparation of fabrics with antimicrobial activity

Silk fabrics were modified by treatment with tannic acid (TA) solution or by acylation with ethylenediaminetetraacetic (EDTA) dianhydride. Kinetics of modification with TA and acylation with EDTA–dianhydride was investigated. The physico‐mechanical properties of silk fabrics acylated with EDTA–dianhydride remained unchanged regardless of chemical modification. The absorption of metal cations (Ag⁺, Cu²⁺) by untreated and modified silk fabrics was studied as a function of the kind of modifying agent, weight gain, and pH of the metal solution. The absorption of Cu²⁺ at alkaline pH was not significantly influenced by chemical modification of the silk substrate. The absorption of Ag⁺ by acylated silk remained at a level as low as untreated silk, while was enhanced by TA. The higher the content of TA, the higher the absorption of Ag⁺. With respect to the pH of the metal solution, the acylation with EDTA–dianhydride enabled silk to absorb and bind metal cations even in the acidic and neutral pH range, where tannic acid had no effect. Medium to high levels of metal desorption were exhibited by untreated and modified silk fabrics towards the metal cations, with the only exception of the silk–tannic acid–Ag complex, which displayed an extraordinary stability. All metal‐containing silks exhibited significant antibacterial activity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 297–303, 2001     

Hydrostatic Pressure Influences HIF-2 Alpha Expression in Chondrocytes

Hypoxia-inducible factor (HIF)-2α is considered to play a major role in the progression of osteoarthritis. Recently, it was reported that pressure amplitude influences HIF-2α expression in murine endothelial cells. We examined whether hydrostatic pressure is involved in expression of HIF-2α in articular chondrocytes. Chondrocytes were cultured and stimulated by inflammation or hydrostatic pressure of 0, 5, 10, or 50 MPa. After stimulation, heat shock protein (HSP) 70, HIF-2α, nuclear factor kappa B (NF-κB), matrix metalloproteinase (MMP)-13, MMP-3, and vascular endothelial growth factor (VEGF) gene expression were evaluated. The levels of all gene expression were increased by inflammatory stress. When chondrocytes were exposed to a hydrostatic pressure of 5 MPa, HIF-2α, MMP-13, and MMP-3 gene expression increased significantly although those of HSP70 and NF-κB were not significantly different from the control group. In contrast, HIF-2α gene expression did not increase under a hydrostatic pressure of 50 MPa although HSP70 and NF-κB expression increased significantly compared to control. We considered that hydrostatic pressure of 5 MPa could regulate HIF-2α independent of NF-κB, because the level of HIF-2α gene expression increased significantly without upregulation of NF-κB expression at 5 MPa. Hydrostatic pressure may influence cartilage degeneration, inducing MMP-13 and MMP-3 expression through HIF-2α.     

Grafting vinyl monomers onto silk (Bombyx mori) using different initiators: Properties of grafted silk

The graft–copolymerization of silk with methacrylamide (MAA), 2‐hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) was studied using three different free‐radical initiators: an inorganic peroxide [ammonium persulfate (APS)] and two azo compounds [2,2′‐azobisisobutyronitrile (AIBN) and 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (ADC)]. The rate and yield of grafting followed the order: APS > AIBN > ADC. The performance of AIBN was close to that of APS in terms of weight gain attained. The degree of yellowing of grafted silk varied as a function of the initiator–monomer system used. APS induced the highest degree of yellowing, regardless of which monomer was used, whereas silk grafted with the MAA/AIBN system displayed the lowest level of yellowing. Moisture regain of grafted silk changed as a function of the hydrophilic/hydrophobic character of the grafted polymer, regardless of the kind of initiator used. Accordingly, tensile properties showed a tendency to decrease with increasing weight gain of grafted silk, the extent of which was independent of the kind of monomer and initiator used. The different initiators did not induce any appreciable change in the fine structure of silk, as demonstrated by optical measurements. Uneven surface deposition of homopolymer was detected to variable extent with MMA and HEMA grafting, whereas the surface of MAA‐grafted silk was completely free of any foreign deposit, independently of the initiator used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1401–1409, 2001     

Estimation of Stress Exponent and Activation Energy for Rapid Densification of 8 mol% Yttria‐Stabilized Zirconia Powder

The rapid densification behavior of 8 mol% Y₂O₃‐stabilized ZrO₂ polycrystalline (8Y‐SZP) powder compacts at the initial stage of pressure sintering (relative density () below 0.92) has been investigated using an electric current‐activated/assisted sintering (ECAS) system. Data points corresponding to a fixed heating rate were extracted from the densification rate () versus ρ and versus temperature (T) curves. These curves were obtained experimentally by consolidation at a fixed current. Under fixed current ECAS, the heating rate () decreases continuously over sintering time. Using a quasi‐ constant heating rate (CHR) method, data points were extracted to plot vs. ρ, vs. T, and ρ vs. T curves at a fixed . The stress exponent (n), estimated from a log‐log plot of grain size (d)‐corrected /ρ and effective stress (σ_eff) at 1300–1400 K, shows an almost constant value of 1. In addition, the activation energy (Q) for rapid densification, estimated from an Arrhenius plot of d‐corrected /ρ also shows an almost constant value of 350 kJ/mol, which is considerably lower than the previously reported value of the activation energy for Zr⁴⁺ lattice diffusion of about 440 kJ/mol. These results suggest that rapid densification of 8Y‐SZP by ECAS seems to proceed by diffusional creep controlled by grain‐boundary diffusion of Zr⁴⁺ ions.     

Production of antimicrobially active silk proteins by use of metal‐containing dyestuffs

The work presented here discusses a new technique for preparing silk fibers and films with persistent antimicrobial activity through use of metallic dyestuffs during the fiber dyeing process. The length of the silk fibers investigated contracted when the fibers were immersed in concentrated neutral salt solutions, such as calcium or potassium nitrate, at elevated temperature levels. The birefringence and molecular orientation of the silk fibroin molecules became less ordered by the action of the neutral salt solutions, resulting in increased dyestuff absorption. Subsequently, contracted silk fibers were dyed with metallic dyestuffs containing Cr or Cu for the purpose of obtaining silk fibers with antimicrobial activity. Silk fibers dyed with metallic dyestuffs showed significant antimicrobial activity against the plant pathogen Cornebacterium and the human pathogen Coli bacillus. Tensile strength of the silk fibers after the salt shrinking and dyeing processes did not show a significant change, whereas the elongation at break was increased slightly. The techniques described here for preparing significantly active antimicrobial silk fibers are effective and economic ways of providing new materials for industrial and biomedical applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1181–1188, 2002     

Reinvestigation of the Oxidative Folding Pathways of Hen Egg White Lysozyme: Switching of the Major Pathways by Temperature Control

It has been well established that in the oxidative folding of hen egg white lysozyme (HEL), which has four SS linkages in the native state (N), three des intermediates, i.e., des[76–94], des[64–80], and des [6–127], are populated at 20 °C and N is dominantly formed by the oxidation of des[64–80] and des[6–127]. To elucidate the temperature effects, the oxidative folding pathways of HEL were reinvestigated at 5–45 °C in the presence of 2 M urea at pH 8.0 by using a selenoxide reagent, DHS^ox. When reduced HEL was reacted with 1–4 equivalents of DHS^ox, 1S, 2S, 3S, and 4S intermediate ensembles with 1–4 SS linkages, respectively, were produced within 1 min. After the oxidation, 3S was slowly converted to the des intermediates with formation of the native structures through SS rearrangement. At 5 °C, des[76–94] was populated in the largest amount, but the oxidation to N was slower than that of des[64–80] and des[6–127]. At 35 °C, on the other hand, des[64–80] and des[6–127] were no longer stable, and only des[76–94] was populated. The results suggested that the major folding pathways of HEL can be switched from one to the other by temperature control.