Phase- and glass-transition phenomena due to the same configurational order–disorder mechanism in crystalline racemic sec-butylcyclohexane

We report molar heat capacities for racemic sec-butylcyclohexane (s-BCH) measured by the adiabatic calorimetric method within the temperature range from 14 to 200 K. In the crystalline state, we identified the presence of a second-order phase transition and a glass transition phenomenon, both originating from the same configurational degree of freedom. The phase and glass transition temperatures T _trs and T _g were determined to be (136.7 ± 1.0) and (100 ± 1) K, respectively. The entropy of phase transition was estimated to be Δ_trs S _m = 1.4 J K^?1 mol^?1 ≈ (1/4) R ln 2. The phase transition was judged to be of an order–disorder type on the basis of the fact that the glass transition occurred in the low-temperature heat-capacity tail. The entropy was interpreted to suggest that four molecules in the crystalline state constitute a unit for producing two distinct configurations in the coexistence of (d)- and (l)-s-BCH.     

Preparation of divinylbenzene copolymer particles with encapsulated hexadecane for heat storage application

From the viewpoint of heat storage application, encapsulation of n-hexadecane (HD) was carried out by microsuspension copolymerizations of divinylbenzene (DVB) and acrylic monomers (butyl acrylate, BA; ethyl acrylate, EA) utilizing the self-assembling of phase-separated polymer (SaPSeP) method proposed by the authors. The heat of solidification (H _s) of encapsulated HD in the micron-sized, cross-linked particles was determined by the differential scanning calorimeter (DSC). H _s of the encapsulated HD in poly(DVB) particles was much lower than that of pure HD, but it was increased with BA or EA content copolymerized up to that of pure HD. Such an influence of encapsulation on the H _s was discussed. Part CCIIIC of the series “Studies on suspension and emulsion”.     

Relation of the number of cross-links and mechanical properties of multi-walled carbon nanotube films formed by a dehydration condensation reaction

Multi-walled carbon nanotube (MWCNT) films were prepared by employing a condensation reaction utilizing 1,3-dicyclohexylcarbodiimide (DCC) to cross-link each MWCNT with carboxylic acid and hydroxyl groups. Morphological changes in the resultant MWCNT films were monitored using scanning electron microscopy and showed that the MWCNTs were randomly intertwined in the films. The prepared MWCNT films were 17 mm in diameter and 20 microm in thickness, and the apparent density was 0.59 g/cm(3). Fourier transform-infrared spectroscopy confirmed that each MWCNT modified with carboxylic acid and hydroxyl groups was cross-linked through the ester bond. It was found that the ratio of the number of ester cross-links and carbon atoms of the nanotubes per unit apparent volume (cm(3)) of condensed-MWCNT films was 5.27 x 10(-3) using thermogravimetric analysis (TGA). The tensile strength and Vickers hardness of condensed-MWCNT films achieved an average of 15 and 9.2 MPa, respectively, and were greater than those of free-standing MWCNT films without ester bond.     

Highly selective and sensitive template-directed photoligation of DNA via 5-carbamoylvinyl-2'-deoxycytidine

We describe a highly efficient template-directed photoligation of oligodeoxynucleotides (ODNs) through 5-carbamoylvinyl-2'-deoxycytidine ((CV)C). When an ODN containing (CV)C at the 5' end was photoirradiated with an ODN containing a pyrimidine base at the 3' end in the presence of template DNA, efficient photoligation was observed without any byproduct formation. Single nucleotide differences can be successfully distinguished by using photoligation-based DNA chip assay. [structure: see text]     

Irreversibility lines of layered Fe-based superconductors with thick blocking layers

Irreversibility lines of the layered iron-arsenide superconductors with thick perovskite-type oxide blocking layers have been systematically studied. Five compounds with different interlayer distance between iron layers from 1.5 to 3.0 nm were selected for the magnetization measurements. These compounds showed very large magnetically reversible region. The irreversibility lines of these compounds were found to locate at very low fields compared to the other iron-based superconductors and shift towards lower fields with an increase in the thickness of the blocking layer. In addition, the analysis on the irreversibility line suggested that the change of dimensionality of the vortex system occurs at $T/T_c～0.6$. These results indicate that the electromagnetic anisotropy originated from the layered crystal structure plays a crucial role to determine the irreversibility line and magnetic phase diagram of layered iron arsenides as is the case in the layered cuprates.     

Targeted sonodynamic therapy using protein-modified TiO2 nanoparticles

Our previous study suggested new sonodynamic therapy for cancer cells based on the delivery of titanium dioxide (TiO₂) nanoparticles (NPs) modified with a protein specifically recognizing target cells and subsequent generation of hydroxyl radicals from TiO₂ NPs activated by external ultrasound irradiation (called TiO₂/US treatment). The present study first examined the uptake behavior of TiO₂ NPs modified with pre-S1/S2 (model protein-recognizing hepatocytes) by HepG2 cells for 24 h. It took 6 h for sufficient uptake of the TiO₂ NPs by the cells. Next, the effect of the TiO₂/US treatment on HepG2 cell growth was examined for 96 h after the 1 MHz ultrasound was irradiated (0.1 W/cm², 30 s) to the cells which incorporated the TiO₂ NPs. Apoptosis was observed at 6 h after the TiO₂/US treatment. Although no apparent cell-injury was observed until 24 h after the treatment, the viable cell concentration had deteriorated to 46% of the control at 96 h. Finally, the TiO₂/US treatment was applied to a mouse xenograft model. The pre-S1/S2-immobilized TiO₂ (0.1 mg) was directly injected into tumors, followed by 1 MHz ultrasound irradiation at 1.0 W/cm² for 60 s. As a result of the treatment repeated five times within 13 days, tumor growth could be hampered up to 28 days compared with the control conditions.     

Free radical polymerization within mesoporous zeolite channels

Free radical polymerization of methyl methacrylate (MMA) within the uniform channels of the mesoporous zeolite MCM-41 proceeds at 100°C to give a high molecular weight polymer (PMMA). The formation of long-living propagating polymer-radicals is observed by electron paramagnetic resonance (EPR). The molecular weight of PMMA within the mesopores can be controlled over a wide range by changing the monomer-to-initiator mole ratio.     

Synthesis and characterization of photorefractive polymers with triphenylamine unit and NLO chromophore unit on a side chain

Acrylate‐type copolymers (TPA‐DCV) consisting of triphenylamine (TPA) unit as a hole transport agent and dicyanovinyl aniline (DCV) as a second‐order nonlinear optical (NLO) chromophore on a side chain were synthesized. The polymers showed good solubility and sufficient morphological stability after film formation. The diffraction efficiency and gain coefficient increased as glass transition temperature decreased TPA‐DCV composite doped with fullerene (C₆₀) and dibutyl phthalate had a high photoconductivity of 5.1 × 10⁻¹² S/cm at the applied electric field of 50 V/µm. Diffraction efficiency and response rate were measured as functions of the parameters determining the photoconductivity (e.g. applied electric field, the density of the photocharges generated and writing beam intensity). The maximum diffraction efficiency and gain coefficient were 12.9% and 64 cm⁻¹, respectively, at an applied electric field of 80 V/µm. The maximum response time of 700 msec was obtained at the applied electric field of 80 V/µm. Photoconductivity, response rate and diffraction efficiency increased with the increase of the applied electric field. Field dependence of the response rate is attributed to the charge generation efficiency and/or the drift mobility. A similar power dependence of the photoconductivity and the response rate on the writing beam intensity was observed. The response rate and diffraction efficiency showed a good linear relationship with the logarithm of the photoconductivity. Copyright © 2000 John Wiley & Sons, Ltd.