Low-temperature Crystallization Method Research Articles

Effect of solvent ratio on omega-3 extraction of catfish (Clarias sp.) and pangasius catfish (Pangasius sp.) using low-temperature crystallization method

Effect of solvent ratio on omega-3 extraction of catfish (Clarias sp.) and pangasius catfish (Pangasius sp.) using low-temperature crystallization method

Amine-free synthesis of high-silica MFI zeolite by the conventional hydrothermal route

High-silica MFI zeolite can hardly be prepared by the conventional hydrothermal synthesis route in the absence of amines, which is ascribed to the competitive growth of quartz, magadiite, or kenyaite phase. In this work, these impurity phases were excluded from the synthetic gel through a low-temperature crystallization method, while the growth of zeolite phase was promoted by seed-directed and C2H5OH filling. Consequently, well-crystallized ZSM-5 samples with controllable Si/Al ratios (46–205) and uniform particle sizes were successfully prepared, and the crystallization process was tracked by multiple characterization techniques, pointing toward a nonclassical particle attachment crystallization process. Interestingly, we found that the optimal C2H5OH/SiO2 ratio can be proportionally reduced by decreasing the H2O/SiO2 ratio in the synthetic gel. More importantly, the obtained high-silica MFI zeolite exhibited a much higher catalytic stability than the conventional sample synthesized using tetrapropylammonium as the template during the methanol-to-propylene and n-butene cracking reactions, which may be attributed to its fewer defect sites determined by 1H magic angle spinning nuclear magnetic resonance techniques. Overall, this work provides an efficient route for the large-scale production of high-silica ZSM-5 samples.

Vacuum-Controlled Growth of CsPbI2Br for Highly Efficient and Stable All-Inorganic Perovskite Solar Cells.

A high-temperature annealing process (>250 °C) is always needed to obtain high-quality α-CsPbI2Br perovskite films, which makes it a challenge in the manufacture and application of flexible photovoltaic devices. In this work, a vacuum-controlled growth (VCG) method that can effectively control the crystallization of perovskite and provide high-quality films with larger grain size and low defect density at a lower temperature is demonstrated. Besides, a facile introduction of polyethyleneimine ethoxylated (PEIE) interlayer improves the charge extraction and suppresses the carrier recombination. Therefore, the power conversion efficiency (PCE) of an all-inorganic CsPbI2Br perovskite solar cell (PSC) reaches 12.32%. The unencapsulated PSCs with VCG treatment and PEIE modification show outstanding stabilities while retaining over 95% of the initial PCE after being stored in a N2 glovebox for 1000 h. This low-temperature crystallization method and cheap interlayer introduction can drive the development of future commercialization of all-inorganic perovskite solar cells.

High-Quality Single Crystal Perovskite for Highly Sensitive X-Ray Detector

Organolead halide perovskites provide tremendous opportunities for ideal radiation detection due to their high atomic numbers, large carrier mobilities, and long lifetimes. Here, we synthesized high-quality single crystal CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> PbBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with a high mobility-lifetime product of 4.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V by the developed inverse low temperature crystallization method. The sensitive X-ray detector was fabricated by depositing 50 nm of gold on both sides of the perovskite crystal. This device exhibited a high sensitivity up to 259.9 μC/Gyair/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> under the 39 keV X-ray exposure at a small electric field of ~0.83 V/mm and yielded a low noise of 3.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-23</sup> A <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz. Additionally, the sensitivity can be further improved by increasing operating voltage. Our results provided a solution for constructing high-performance X-ray detectors.

Review—Technology Trends of Poly-Si TFTs from the Viewpoints of Crystallization and Device Performance

Thin-film transistors (TFTs) utilizing low-temperature polycrystalline-Si (LTPS) are critical for system-on-panel applications. The requirements for LTPS are a high quality, a large grain size and position control of the nucleation. Many promising crystallization methods have been developed to satisfy these requirements. Herein, two scientific discoveries related to the low-temperature crystallization and high-performance TFT structure using the tunnel effect are introduced. Hydrogens in an amorphous (a-Si) film greatly accelerate the crystal velocity and improved the crystallinity of the excimer-laser annealing (ELA) poly-Si film, thereby providing a high-quality, a large-grained film referred to as secondary-grain film, under the solid-phase condition. In addition, a soft X-ray crystallization (SXC) method was developed. It reduces the threshold temperature of crystallization for a-Si, SiXGe1-X and Ge films by 100°C–140°C in comparison to that for films prepared by conventional thermal crystallization. The SXC method is expected to become the critical low-temperature crystallization method in the era of the flexible electronics. On the other hand, although high-performance TFTs that utilize large single-crystalline grains have been intensively researched, such research has not been successful from the viewpoint of mass production. A novel device structure – tunneling dielectric TFT (TDTFT)–has been developed. The TDTFT reduces the gate-off current to less than 1/10 of that with a conventional TFT. In addition, the TDTFT improved the hump effect. We conclude that the triple-gate (Fin) TDTFT will be a promising candidate for next-generation poly-Si TFT structures.

New Mechanistic Insight of Low Temperature Crystallization of Anodic TiO2 Nanotube Array in Water

A facile low-temperature crystallization method was recently developed for the synthesis of anodic TiO2 nanotubes (NTs). This novel method requires less energy and less sophisticated equipment than traditional high-temperature sintering, but the underlying mechanisms have not yet been elucidated. Here, we systematically studied the low-temperature crystallization mechanism of anodic TiO2 NTs by using different solvents and treatment time. For the first time, we notice a dramatic change of the surrounding water and discuss the TiO2 nanocrystals (NCs) byproducts of the low-temperature crystallization process. Accordingly, we propose a dissolution–recrystallization mechanism in which dissolved Ti(OH)62– dehydrates and crystallizes in situ to form anatase NTs as well as anatase NCs. Overall, this work provides a mechanistic insight into this low-temperature crystallization method, which could benefit the optimization and scale-up of industrial TiO2 NT production.

Evaluation of physical property for syndiotactic PVA-H by hot pressing method

Event Abstract Back to Event Evaluation of physical property for syndiotactic PVA-H by hot pressing method Tomoyo Sakaguchi1, Shusaku Nagano2, Mitsuo Hara3, Yoshihiro Kimura4, Akinobu Oharuda4 and Kazuaki Matsumura1 1 Japan Advanced Institute of Science and Technology, School of Materials Science, Japan 2 Nagoya University, The Nagoya University Venture Business Laboratory, Japan 3 Nagoya University, Graduate School of Engineering, Japan 4 JAPAN VAM & POVAL CO.,LTD., Reserch and Developement Dept., Japan Introduction: We have investigated poly(vinyl alcohol) (PVA) hydrogel as a biomaterial for a replacement for artificial articular cartilage because of its excellent mechanical properties, biocompatibility, and low friction coefficient[1],[2]. PVA hydrogels are physical gels with small crystalline as crosslinking points and have been prepared by low temperature crystallization method[3]. In order to prepare PVA hydrogels having high mechanical properties, a mixed solvent of dimethyl sulfoxide (DMSO) and water should be used to prevent freezing of the solvent and phase separation during freezing. In our previous study, we successfully prepared transparent PVA hydrogel without using toxic DMSO from high concentrated PVA aqueous solution by hot pressing method[4]. In this study, we intended to prepare mechanically stronger hydrogels from syndiotactic PVA (s-PVA) by using hot pressing method because s-PVA is difficult to be dissolved in water by usual heating and stirring method due to its high crystallinity. Material and Methods: In hot pressing method, atactic PVA (a-PVA) or s-PVA (Japan VAM & POVAL Co. Ltd., degree of polymerization 1700, degree of saponification 99.0%), [s]-traid value, a-PVA : 30%, s-PVA : 36%) was mixed with H2O at a concentration of 40 w/w%. The swollen PVA/H2O was pressed at 0-20 MPa and 95-130 oC for 30 min, then kept at room temperature without drying for gelation one week. After 2 days vacuum drying, gels were heated in vacuum to control the water content. While gelation time, we conducted tensile test to evaluate the gelation speed of each PVA hydrogel from Young’s modulus. And we also measured small angle X-ray scattering (SAXS) to evaluate the developing speed of crystalline in PVA hydrogel. Results and Discussion: By hot pressing method, transparent hydrogels were obtained with s-PVA, because of the fast crystallization, even at room temperature. Fig 1. Syndiotactic PVA hydrogel by hot pressing method Water content was well controlled by heating of dried gel due to the increasing of crystallinity. When we use a-PVA, around 35 % is minimum water content. But when we use s-PVA, we succeeded in preparing around 30 % water content PVA hydrogel. Tensile test revealed that s-PVA hydrogel showed higher Young’s modulus in each gelation time, showing faster gelation than a-PVA hydrogel . Fig 2. Time dependence of Young’s modulus during gelation time Faster crystallization in s-PVA was confirmed by SAXS measurement. It revealed that diffraction peak in s-PVA hydrogel appeared at one day after preparation. On the other hand, diffraction peak of a-PVA, appeared at 30 days after preparation. Conclusion: By using s-PVA, we succeeded in preparing transparent PVA hydrogel with higher mechanical property and lower water content than a-PVA. And s-PVA hydrogel showed faster gelation and crystallization time than a-PVA hydrogel. From these results, mechanically robust hydrogel which might be suitable for the articular cartilage implant could be developed by using hot pressing method and s-PVA.

Hydrogel formation from the concentrated aqueous solution of polyvinyl alcohol

ABSTRACTPhysically crosslinked polyvinyl alcohol (PVA) hydrogels with high mechanical properties can be made by a low temperature crystallization method using a mixed solvent of dimethyl sulfoxide (DMSO) and water. Such hydrogels are studied as the artificial articular cartilage material. But DMSO shows cytotoxycity, and it is also have the effect of accelerating the absorption of harmful substances. Therefore completely elimination must be required for clinical application but the process is difficult.However, PVA hydrogel made by water as a sole solvent by freeze-thawing method became cloudy because of micro-heterogeneous structure, and shows low mechanical properties.Therefore, in this study, we developed the novel hot pressing method for preparing transparent and uniformly cross-linked PVA hydrogels without DMSO from highly concentrated aqueous solution. By this method, PVA hydrogels with high mechanical property and high transparency can be obtained without any harmful organic solvent because of the fast crystallization even at room temperature. The mechanical properties of PVA hydrogels were remarkably depended on their water contents after gelation, regardless of solution concentration.

A Simple New Way to Prepare Cu-Doped Nano-TiO&lt;sub&gt;2&lt;/sub&gt; with Visible Light Photocatalytic Activity

Cu-doped TiO2 photocatalysts were synthesized by a homogeneous hydrolysis and low temperature crystallization method using tetrabutyl titanate as the titanium source and cupric acetate as the doping agent. The phase structure, composition and morphology of the product were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and Brunauer-Emmett-Teller surface area analysis (BET). The XRD results confirmed that the crystalline phase of all prepared samples was anatase-type TiO2. SEM results showed that the Cu-doped TiO2 were composed of spherical particles with particle diameter smaller than 20 nm. Furthermore, the photocatalytic activity of the Cu-doped TiO2 catalysts were evaluated based on the photocatalytic degradation of methyl orange (MO) in aqueous solution. The results showed that Cu-doped TiO2 had the higher visible-light-induced catalytic activity than the commercial P25 TiO2 powder. The copper content in Cu-doped TiO2 had obvious effect on the visible-light-induced catalytic activity, and the degradation rate of MO could reach 33.7% using Cu-doped TiO2 with a doping level of 1.0 mol% Cu as a photocatalyst under the visible light irradiation for 3 hours.

Measurements of Dynamic Viscoelasticity of Poly (vinyl alcohol) Hydrogel for the Development of Blood Vessel Biomodeling

In vitro blood vessel biomodeling with realistic mechanical properties and geometrical structures is helpful for training in surgical procedures, especial those used in endovascular treatment. Poly (vinyl alcohol) hydrogel (PVA-H), which is made of Poly (vinyl alcohol) (PVA) and water, may be useful as a material for blood vessel biomodeling due to its low surface friction resistance and good transparency. In order to simulate the mechanical properties of blood vessels, measurements of mechanical properties of PVA-H were carried out with a dynamic mechanical analyzer, and the storage modulus (G’) and loss modulus (G”) of PVA-H were obtained. PVA-Hs were prepared by the low-temperature crystallization method. They were made of PVA with various concentrations (C) and degrees of polymerization (DP), and made by blending two kinds of PVA having different DP or saponification values (SV). The G’ and G” of PVA-H increased, as the C or DP of PVA increased, or as the proportion of PVA with higher DP or SV increased. These results indicate that it is possible to obtain PVA-H with desirable dynamic viscoelasticity. Furthermore, it is suggested that PVA-H is stable in the temperature range of 0°C to 40°C, indicating that biomodeling made of PVA-H should be available at 37°C, the physiological temperature. The dynamic viscoelasticity of PVA-H obtained was similar to that of the dog blood vessel measured in previous reports. In conclusion, PVA-H is suggested to be useful as a material of blood vessel biomodeling.

水素変調ドープ a-Si 膜のエキシマレーザアニーリング

A novel low-temperature crystallization method is proposed; the excimer laser annealing (ELA) of amorphous silicon (a-Si) with a hydrogen-modulation-doped layer (ELHMD). The effects of hydrogen on low-energy crystallization by conventional ELA and ELHMD were investigated. As the hydrogen concentration increases, the crystallinity of the polycrystalline silicon (poly-Si) prepared at a low energy density improves. It is considered that the nucleation is enhanced by the desorption energy of hydrogen from the Si-H2 bond during the Si melting. In addition, the film exfoliation by H2 burst can be suppressed using HMD a-Si film.

Excimer Laser Annealing of Hydrogen Modulation Doped a-Si Film

A novel low-temperature crystallization method is proposed; the excimer laser annealing (ELA) of amorphous silicon (a-Si) with a hydrogen-modulation-doped layer (ELHMD). The effects of hydrogen on low-energy crystallization by conventional ELA and ELHMD were investigated. As the hydrogen concentration increases, the crystallinity of the polycrystalline silicon (poly-Si) prepared at a low energy density improves. It is considered that the nucleation is enhanced by the desorption energy of hydrogen from the Si-H2 bond during the Si melting. In addition, the film exfoliation by H2 burst can be suppressed using HMD a-Si film. [doi:10.2320/matertrans.48.975]

Nanostructured titania membranes with improved thermal stability

Nanostructured titania membranes have received significant attention in recent years because of their unique characteristics such as high water flux, semiconductance, photocatalysis, and chemical resistance over other membrane materials including γ -alumina, silica and zirconia [1, 2]. The potential applications of titania membranes include ultrafiltration processes and catalytic/photocatalytic membrane reactor systems for liquid and gas separations [3, 4]. However, their practical applications are limited due to the reduction of porosity and surface area at the elevated temperatures. Hydrothermal process is a low temperature crystallization method, which can produce thermally stable crystalline titania particles [5]. Although hydrothermal process has been used as an independent process to produce ultrafine crystalline oxide particles, this process can be also combined with sol-gel process to promote crystallization of sol-gel products under mild conditions. In this work, hydrothermal process was combined with sol-gel process to improve the thermal stability of titania membranes. Titania sol was prepared by hydrolysis and condensation of titanium isopropoxide (TTIP, Ti(OC3H7)4, 97%), followed by peptization [6]. The TTIP was first dissolved in anhydrous ethyl alcohol at a C2H5OH/TTIP molar ratio of 5. Hydrolysis and condensation were conducted at room temperature, by adding the mixed solution slowly into distilled water up to an H2O/TTIP molar ratio of 200. The white precipitates were centrifuged and washed with distilled water. After redispersing the precipitates in the certain amount of water, a 1 M HNO3 solution was added to the white precipitates to attain a [H+]/[Ti] molar ratio of 0.3–0.5. Then, the solution was refluxed at 80 ◦C for 12 hr. For hydrothermal treatment, the peptized sol was transferred into Teflon beaker in the metal jacket (autoclave) and the autoclave was aged at 135 ◦C for 12 hr. Unsupported titania membranes were prepared by pouring peptized sol and hydrothermally treated sol into petri dishes, followed by drying under the controlled atmosphere. The dried membranes were fur-

Receptor-mediated targeting of lipobeads bearing acetohydroxamic acid for eradication of Helicobacter pylori

In the present context, phosphatidyl ethanolamine (PE) liposomes anchored polyvinyl alcohol (PVA) xerogel beads (lipobeads) bearing acetohydroxamic acid (AHA) was developed as a receptor-mediated drug delivery system for use in blocking adhesion of Helicobacter pylori and thereby preventing the sequelae of chronic gastric infections. PVA beads containing AHA were prepared by emulsification followed by low temperature crystallization method. Surface acylation with fatty acid chain was accomplished by treating PVA bare beads with palmitoyl chloride. The completion of this reaction was characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) which confirmed the formation of an ester bond. Final formation of lipobeads was accomplished by combining acylated PVA beads with a PE liposome suspension. To confirm the specific binding propensity of lipobeads towards the PE specific surface receptors of H. pylori, we have performed in situ adherence assay and radiolabelling assay with human stomach cells and KATO-III cells, respectively. In both of these studies, pretreatment of H. pylori with lipobeads completely inhibited the adhesion of H. pylori to human stomach cells and KATO-III cells. These assays could serve as suitable in-vitro models for the study of binding efficacy of lipobeads with H. pylori surface receptors . In addition, the antimicrobial activity of the formulations was evaluated by growth inhibition (GI) studies with isolated H. pylori strain. The inhibitory efficacy of lipobeads was significantly higher compared to that of PVA bare beads. These results suggest that lipobeads could be a potential targeted drug delivery system in the treatment of H. pylori.

Characterization of a polyvinyl alcohol-hydrogel artificial articular cartilage prepared by injection molding

We have developed a hip hemi-arthroplasty using polyvinyl alcohol-hydrogel (PVA-H) as the treatment for hip joint disorders in which the lesion is limited to the joint surface. In previous studies, we characterized the biocompatibility and the mechanical properties of PVA-H as an arthroplasty material. To fix PVA-H firmly to the bone, we have devised an implant composed of PVA-H and porous titanium fiber mesh (TFM). However, because of poor infiltration of the PVA solution into the pores of the TFM when using the low temperature crystallization method, the strength of the PVA-H-TFM interface was insufficient. Consequently, the infiltration method was improved by adopting high-pressure injection molding. With this improved method, the bonding strength of the interface increased remarkably. However, as this injection molding requires high temperature, various mechanical properties of the PVA-H might change with this treatment in comparison with the previous method. The purpose of this study was to investigate the effect of high temperature treatment on the mechanical properties of PVA-H as artificial articular cartilage, the tensile test and friction test were performed about new PVA-H. The results showed no significant mechanical deterioration of the PVA-H. This certified that the injection-molding method did not induce the change of the mechanical properties of PVA-H and indicated the potential of hemi-arthroplasty using PVA-H by this method in the future.

Preparation of Poly-Ge Considering its Application to a-Si/Poly-Ge Multilayer Structures by a Low-Temperature Solid Phase Crystallization Method

Poly-Ge films with good crystallinity were prepared by a low-temperature solid phase crystallization (SPC) method for application to multilayer a-Si/poly-Ge structures. Using a-Ge:H films prepared at just below the thermal decomposition temperature of GeH4 gas as the starting material for SPC, high-quality poly-Ge with Ge<111> peak orientation was obtained after low-temperature annealing at 350°C for 2 h in a nitrogen atmosphere. Furthermore, the selective crystallization of a-Ge:H sublayers in an a-Si:H( ∼50 Å)/a-Ge:H( ∼1000 Å) multilayer film was achieved by annealing at 350°C. The poly-Ge sublayers included large crystal grains with dimensions of about 3000 Å, which were three times as thick as the poly-Ge sublayers.

Low temperature poly-Si thin-film transistor fabrication by metal-induced lateral crystallization

A new low temperature crystallization method for poly-Si TFTs was developed: Metal-Induced Lateral Crystallization (MILC). The a-Si film in the channel area of a TFT was laterally crystallized from the source/drain area, on which an ultrathin nickel layer was deposited before annealing. The a-channel poly-Si TFTs fabricated at 500/spl deg/C by MILC showed a mobility of 121 cm/sup 2//V/spl middot/s, a threshold voltage of 1.2 V, and an on/off current ratio of higher than 10/sup 6/. These electrical properties are much better than TFTs fabricated by conventional crystallization at 600/spl deg/C.

Design of a polyvinyl alcohol hydrogel containing phospholipid as controlled-release vehicle for rectal administration of (±)-propranolol HCl

Polyvinyl alcohol hydrogels which contained phospholipid, egg yolk lecithin or hydrogenated soya lecithin were designed as a transrectal delivery system for propranolol hydrochloride. The hydrogel preparations containing phospholipid were prepared by a low-temperature crystallization method. The release profile of propranolol from hydrogel preparations containing phospholipid complied with Fickian diffusion (Higuchi model). The release of propranolol from the hydrogel preparation decreased with higher contents of phospholipid (approximately 2% w/w). In rats plasma concentrations of propranolol after rectal administration of hydrogel preparations containing phospholipid (1 and 2% w/w) were prolonged compared with those of rats receiving preparations without phospholipid.

Evaluation of Polyvinyl Alcohol Hydrogel as Sustained-Release Vehicle for Transdermal Sytem of Bunitrolol-HCL

AbstractIn order to evaluate a bunitrolol (β-blocker preparation using poly(vinyl alchol) (PVA) hydrogel for hypertension as a transdermal delivery system, in vitro release characteristics and the permeation of bunitrolol through rat sking from hydrogel and the bunitrolol plasma profile after application onto abdominal skin in rats were examined. The PVA hydrogel containing bunitrolol-HCl was prepared by a low temperature crystallization method. The release of bunitrolol from PVA hydrogel followed with Ficklan diffusion (Higuchi model); the drug relaase, profile versus square root of relase. The release rate and premeation through rat skins of bunitrolol from hydrogels affected with preparation at various physical and chemical states. Longer freezing times, higher polymerization and higher concentration of PVA resulted in lower permeation. These results had relations with the results of release tests. Higher pH of preparation resulted in a higher permeation of bunitrolol, which did not have a relaion with...

Evaluation of polyvinyl alcohol hydrogel as a sustained-release vehicle for rectal administration of indomethacin.

In order to evaluate an indomethacin polyvinyl alcohol (PVA) hydrogel for rectal administration, the in vitro release characteristics of indomethacin from the hydrogel and indomethacin plasma concentrations after rectal administration were examined. The PVA hydrogel containing indomethacin was prepared by a low-temperature crystallization method. The release of indomethacin from the PVA hydrogel agreed with the Fickian diffusion model for 10 hr. Rectal administration of indomethacin hydrogels to rats yielded high indomethacin plasma concentrations, without producing a sharp peak, and a sustained-release effect. In dogs, the indomethacin hydrogel produced a similar sustained-release effect; however, the indomethacin plasma concentration was relatively low compared with that of an indomethacin suppository.