Papers by Keyword: Phase Separation

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Authors: Jin Ik Lim, Gun Woo Kim, Jae Sik Na, In Sup Noh, Young Sook Son, Chun Ho Kim
Abstract: This study is to develop a novel method for preparation of the chitosan scaffold having interconnected open pore structure and controlled pore distribution. For this, the effects of addition of non-solvent on chitosan solution were estimated. The porous scaffolds were typically prepared by solid-liquid separation and subsequent sublimation of solvent. Alcohol was used as non-solvent for chitosan. The difference of freezing temperature of each of the components induced the liquidliquid and the liquid-solid phase separation via demixing solution (solvent/non-solvent/chitosan). The morphology, heterogeneous pore distribution and mechanical properties of the scaffolds were examined. The addition of non-solvent in chitosan solution was to make the controlled homogeneous micropores and improved interconnectivity between pores without any surface skin layer. For control chitosan scaffold, the pore size was mainly about 80~100 μm. On the contrary, Pore diameters could be controlled mainly within the range 30~100 μm, with a variation of solvent/non-solvent ratio. The number of minute pore (4~25 μm) over chitosan scaffold increased with increasing ratio of non-solvent. New prepared scaffold exhibited larger value of breaking elongation, more elasticity, but less tensile strength than that of control scaffold.
Authors: S. Konidaris, E. Welser, F. Dimroth, Efstathios K. Polychroniadis
Abstract: Quaternary semiconductor alloys based on GaSb are suitable for thermo-photo voltaic cell applications as they have low and adjustable band-gap. However, they exhibit phase separation which destroys band-gap uniformity. In this work, GalnAsSb thin films grown on GaSb vicinal substrates were studied by Transmission Electron Microscopy, in order to determine the influence of the growth parameters on phase separation. It was found that the coatings exhibit two types of compositional modulation, one parallel and the other forming an angle with the substrate plane.
Authors: M. Singh, K.L. Bhatia, P. Singh, R.S. Kundu, N. Kishore
Authors: John L. West, Jun Ren Wang, Antal Jákli
Abstract: We report formation of complex responsive fibers consisting of a low molecular weight liquid crystal (LC) core surrounded by a polymer sheath using simple airbrush or jet spraying techniques. The fibers are formed using a solution of LC and polymer dissolved in a common solvent. With proper control of the solution composition and formation conditions the fibers self‐assemble. The diameter of the resulting fibers can be adjusted over a range spanning from one to tens of microns. The core of the fiber retains all of the responsive properties associated with low molecular weight LCs. A nematic LC core's director aligns along the long axis of the fiber making them highly birefringent. An electric field applied across the fiber changes both the director alignment and the optical properties of the fiber. Alternatively, thermochromic fibers are formed using a cholesteric LC in the core. Unlike similar electrospun fibers, the airbrushed fibers can be sprayed as continuous mats on virtually any surface or woven into textiles. The resulting fabrics can be made into displays, thermochromic temperature sensors, or for detection of chemical or biological agents. They offer numerous opportunities for wearable textiles that respond optically to a variety of stimuli.
Authors: Iva Tkalcec, Daniele Mari, Robert Schaller
Abstract: A relaxation peak has been observed in the internal friction spectrum of 18-carat AuAgCu yellow gold alloys at about 750K for 0.5Hz. It is related to the presence of grain boundaries, since it is absent in the spectrum of single crystals. For the 14-carat yellow gold alloy (Au38%Ag32%Cu30%), a phase decomposition between silver-rich and copper-rich solid solution occurs in the same temperature range. The effects of the phase decomposition on the internal friction and the dynamic modulus are studied by isochronal and isothermal measurements and correlated with the microstructure evolution. Upon cooling, the phase decomposition starts at grain boundaries at about 840K, producing a fine lamellar structure, and the grain boundary peak amplitude strongly decreases. As the phase decomposition progresses at the interior of the grains upon further cooling, the internal friction background increases. It remains very high in heating until solid solution homogenisation, which occurs above 890K. Such an increase of the internal friction background is observed also in the single crystalline alloy and may be attributed to the interfaces between lamellae of the silver and copper-rich phase.
Authors: Michael Shepilov, Olga Dymshits, Valerii V. Golubkov, Alexander A. Zhilin
Abstract: An evolution of the structure of three glasses of Na2O-Nb2O5-SiO2 system in the course of isothermal heat treatments at 660–700°C and the extinction coefficient of the material were studied. Spinodal phase separation was found to be a primary process followed by precipitation of nano-sized NaNbO3 crystalline phase. It was found that the spectral dependence of the extinction coefficient in the wavelength range λ= 400–800 nm corresponds to light scattering by spinodal structure at the phase separation stage and by independent Rayleigh scatterers (NaNbO3 nanocrystals) at the early stage of crystallization. The extinction coefficient increases at the first half of the crystallization stage and then decreases. At the late stage of crystallization and for the final glass-ceramics, the extinction coefficient α is 10–20 times smaller than that calculated for independently scattering nanocrystals and is characterized by anomalous wavelength dependence (α ∝ λ−6). The model for calculation of extinction coefficient is proposed, in which the interference effects in light scattering by nanocrystals are taken into account. On this basis, the variation of extinction coefficient in the course of crystallization and its wavelength dependence are explained.
Authors: Liang Ge, Jin Yuan Yao, Hong Wang, Gui Fu Ding
Abstract: In this paper, we prepared an octadecyltrichlorosilane(OTS) super-hydrophobic film using phase separation method to demonstrate the anti-icing property of super-hydrophobic surfaces. We investigated the super-hydrophobicity of the surface in -5°C environment, as well as the icing process of water droplets on the surface which proceeded at the temperature low to -15°C. We found that the prepared OTS film retained its super-hydrophobicity in the -5°C environment by the measurement of contact angle. It was observed that the icing progress of water droplets on the super-hydrophobic surface was greatly retarded. Based on the classical heterogeneous nucleation theory, it concluded that the ice formation is directly related to the surface wettability. This research would be beneficial to the preparation of anti-icing films.
Authors: K.F. Wang, X.P. Liu, Q.C. Li, Y. Wang, L.F. Wang, S. Dong, H. Yu, J.M. Liu
Abstract: The effects of A-site cation size disorder in ABO3 type ferromagnetic metallic La0.55Ca0.45MnO3 system have been studied by substituting La3+ and Ca2+ by other ions, while keeping the valency of Mn ions and the A-site cation mean radius constant in the substituted compounds with different A-site ionic radii variance σ2 = Σi (xiri 2 − 2), where xi and ri are the atomic fraction and ionic radii of i-type ions at A-site, respectively. It is revealed that the A-site disorder induces the decreasing of the magnetization and the increasing of the resistivity. The ferromagnetic Curie point TC decreases with the increasing of the A-site ionic radii variance, too. Moreover, the ground state of the system transits from ferromagnetic metal to glass insulator upon increasing variance of the A-site ionic radii from 0.0003 for La0.55Ca0.45MnO3 to 0.009 for Gd0.55Sr0.45MnO3. It is argued that the suppression of the ferromagnetism is ascribed to the enhanced radial distortion of the MnO6 octahedra due to the increasing A-site disorder.
Authors: Young Ho Kim, Hyo Sub Kim, Sang Jin Han, Chu Sik Park, Ki Kwang Bae, Jong Gyu Lee
Abstract: The sulfur-iodine (SI) cycle, thermochemical water splitting using heat energy from nuclear, is one of the most promising methods for massive hydrogen production. For continuous operation of Bunsen reaction section in SI process, the reactants (SO2, I2 and H2O) were fed to the reactor and the products (a H2SO4 phase and a HIx phase) were sent to storage tanks continuously during the reaction. In this study, we investigated the phase separation characteristics of continuous Bunsen reaction on the reactor shape and temperature. It was found that the reactor shape has little affected on the composition of Bunsen products. It was also observed that the phase separation characteristics of the continuous Bunsen reaction were similar to those for the semi-batch Bunsen reaction.
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