Synergistic effect of composite template and La-doping on microdynamic behavior of photogenerated carriers in mesoporous nano-TiO2

The traditional view that the role of the composite template that is adopted in the preparation of nano-TiO₂ is only for forming a pore structure and increasing the material's specific surface area is challenged by this study. The complex impact of the composite template and La-doping on the microdynamic behavior of photo-generation free charge carriers (FCCs) in the mesoporous nano-TiO₂ is investigated using the transient photovoltaic (TPV) technique, supplemented by electric field-induced surface photovoltaic spectroscopy and a computer simulation method. The experimental results reveal that utilizing an appropriate composite template, such as polyethylene glycol and octadecylamine with a molar ratio of 1:1, may result in the rapid separation and prolonged diffusion distance of electron–hole pairs that were excited by a 355 nm and 50 μJ laser pulse. These may be responsible for the stronger and broader TPV response in the microsecond and millisecond regions of the La-doped nano-TiO₂ in TPV spectroscopy, as compared with that for materials that used other composite templates. This response is closely related to the reduced content of the surface state located at 367 nm. A suitable level of La-doping, however, was only responsible for the stronger and broader TPV response in the microsecond region of the spectrum of the nano-TiO₂. The computer simulation results confirm that the photo-generation FCCs microdynamic characteristics in the microsecond region may partially originate from the state density distribution of both the d-electron in the antibonding orbital and the p-electron in the bonding orbital moving up to higher levels, and from a broader band-gap after La-doping in the anatase lattice cell.     

Neodymium substitution effects in sol–gel derived Y3−xNdxAl5O12

Yttrium aluminium garnet (YAG) powders substituted by neodymium Y_3−xNd_xAl₅O₁₂ (x = 0.1, 0.25, 0.35, 0.5, 0.6, 0.7, 0.8, 1.5, 2.0, 2.5, and 3.0) were prepared by a simple aqueous sol–gel method using aluminium nitrate nonahydrate, yttrium oxide, neodymium oxide as the starting materials and ethane-1,2-diol as complexing agent. The powders annealed at 1000 °C in air were characterized by X-ray diffraction (XRD) analysis, infrared (IR) spectroscopy and scanning electron microscopy (SEM). It was demonstrated, however, that the total substitution of yttrium by neodymium does not proceed in the YAG. Pure cubic garnet phase was formed only at low concentration of neodymium (x = 0.1, 0.25, 0.35, 0.5, 0.6, 0.7, 0.8 and 1.5). With further substitution, when the amount of neodymium was x = 2.0, 2.5 and 3.0 the main part of garnet phase transformed in to the perovskite neodymium aluminate (NdAlO₃) phase.     

Co-processing as a tool to improve aqueous dispersibility of cellulose ethers

Cellulose ethers are important materials with numerous applications in pharmaceutical industry. They are widely employed as stabilizers and viscosity enhancers for dispersed systems, binders in granulation process and as film formers for tablets. These polymers, however, exhibit challenge during preparation of their aqueous dispersions. Rapid hydration of their surfaces causes formation of a gel that prevents water from reaching the inner core of the particle. Moreover, the surfaces of these particles become sticky, thus leading to agglomeration, eventually reducing their dispersion kinetics. Numerous procedures have been tested to improve dispersibility of cellulose ethers. These include the use of cross-linking agents, alteration in the synthesis process, adjustment of water content of cellulose ether, modification by attaching hydrophobic substituents and co-processing using various excipients. Among these, co-processing has provided the most encouraging results. This review focuses on the molecular mechanisms responsible for the poor dispersibility of cellulose ethers and the role of co-processing technologies in overcoming the challenge. An attempt has been made to highlight various co-processing techniques and specific role of excipients used for co-processing.     

Development of topical hydrogels of terbinafine hydrochloride and evaluation of their antifungal activity

The purpose of this study was to prepare hydrogels and microemulsion (ME)-based gel formulations containing 1% terbinafine hydrochloride (TER-HCL) and to evaluate the use of these formulations for the antifungal treatment of fungal infections. Three different hydrogel formulations were prepared using chitosan, Carbopol® 974 and Natrosol® 250 polymers. A pseudo-ternary phase diagram was constructed, and starting from ME formulation, a ME gel form containing 1% Carbopol 974 was prepared. We also examined the characteristic properties of the prepared hyrogels. The physical stability of hydrogels and the ME -based gels were evaluated after storage at different temperatures for a period of 3 months. The release of TER-HCL from the gels and the commercial product (Lamisil®) was carried out by using a standard dialysis membrane in phosphate buffer (pH 5.2) at 32?°C. The results of the in vitro release study showed that the Natrosol gel released the highest amount of drug, followed by Carbopol gel, chitosan gel, commercial product, and the microoemulsion-based gel in that order. In vitro examination of antifungal activity revealed that all the prepared and commercial products were effective against Candida parapsilosis, Penicillium, Aspergillus niger and Microsporum. These results indicate that the Natrosol®-based hydrogel is a good candidate for the topical delivery of TER-HCL.     

Cohesively Enhanced Conductivity and Adhesion of Flexible Silver Nanowire Networks by Biocompatible Polymer Sol–Gel Transition

Silver nanowire (AgNW) networks are a promising candidate to replace indium tin oxide (ITO) as transparent conductors. In this paper, a novel transparent composite conductor composed of AgNW/biocompatible alginate gel on a flexible polyethylene terephthalate (PET) substrate, with synchronously enhanced adhesion and reduced resistivity, is prepared without high‐temperature annealing. The sheet resistance of the flexible AgNW/PET film reduces from 300 to 50.3 Ohm sq^?1 at transmittance of 94%. The optical and electrical performance is superior to that obtained from the flexible ITO film on PET. Meanwhile, the sheet resistance does not show great change after tape test, suggesting a good adhesion of AgNW to the polymer substrate. Moreover, the AgNW composite film shows a good stability to resist long‐term storage, solvent damage, and ultrasonication. Finally, polymer solar cells employing the composite AgNW film as the electrode are realized, displaying an efficiency of 2.44%.     

Design of Porous Alginate Hydrogels by Sacrificial CaCO3 Templates: Pore Formation Mechanism

Fabrication of porous alginate hydrogels with a well‐controlled architecture useful for tissue engineering is still a challenge. Here, CaCO₃‐based templating is utilized to design stable alginate gels with controlled pore dimensions in the range of 5–50 μm. The mechanism of pore formation is studied considering two factors affecting the pore size: i) osmotic pressure generated during the dissolution of sacrificial CaCO₃ templates and ii) alginate gel network density. Osmotic pressure can achieve an upper limit of 100 MPa but does not affect the gel porosity. Additional osmotic pressure (range of kPa) induced by dextrans pre‐encapsulated into CaCO₃ vaterite is also insufficient for pore enlargement. Pore stability depends merely on the gel network density and on the number of crosslinking calcium ions provided locally per unit time; pores are collapsed when template dissolution is too slow or if there is insufficient alginate concentration (below 2%). Young's modulus indicates the soft nature of the prepared hydrogels (tens of kPa) applicable as soft porous scaffolds with a tuned internal structure.     

硅铝凝胶制备与晶化研究

本文以铝胶和硅胶为原料,采用溶胶-凝胶方法进行了硅铝凝胶形成及晶化行为研究.结果表明,要形成稳定铝硅溶胶pH值必须控制在3以下,采用氨水和乙酰丙酮可调节胶凝时间.采用XRD和TEM研究了凝胶和不同温度热处理之后粉体组成和结构,从干凝胶至莫来石的整个形成过程首先是生成硅铝尖晶石,然后才是莫来石,所得到的粉体存在较为严重的二次团聚.在硅铝凝胶中引入氟化铝有助于莫来石晶须生成.     

Effects of Various Viscosity Enhancers and pH on Separating Haem from Porcine Red Blood Cells

Haem derived from animal blood is a valuable source of organic iron which may be used as a supplement in foods. The purpose of this study was to examine the effects of sodium carboxymethyl cellulose (NaCMC), propylene glycol alginate (PGA) and sodium alginate (SA) as viscosity enhancers on the separation of haem from porcine red blood cells, and on the distribution of iron between the haem and non-haem fractions of the extracts. Iron determinations were carried out spectrophotometrically on the supernatants obtained by centrifuging the cell suspensions and on two successive washings of the cells. In the first washings the total extracted iron content using NaCMC was highest when a high-viscosity grade was used; there were no significant differences (P>0·05) between the results obtained with this material and those obtained using PGA or SA. There were also no significant differences (P>0·05) among the three treatments in terms of non-haem content. The absorbances at 540nm of the first washings were lower when the washing was carried out at pH 1·4 rather than at pH 1·0 or 2·0. There were no significant differences associated with changes in the viscosity enhancer in the absorbances of the second washings, but the absorbances at pH 1·4 were generally higher than those at pH 1·0 or 2·0. Enhancement of the absorbances on the addition of 1,10-o-phenanthroline indicated that the extracted iron was present in the ferrous form.     

Studies of temperature and time-dependent network formation in commercial epoxy resins using modified imidazole curing agents

Two commercial epoxy resins, MY750 and MY720, were cured over a range of cure temperatures with a series of novel curing agents based on modified imidazoles. A combination of techniques, including dynamic viscometry, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, high performance and gel permeation chromatography, were used to analyse the reaction mixture. It appears that for a given formulation and given resin, the viscosity behaviour near gelation is different for different cure temperatures and the mechanism appears to be dependent not only on the nature of the imidazole curing agent, but also on the cure temperature. Higher temperature cure appears to lead to the formation of a less ‘homogeneous’ reaction mixture at the gel point, containing oligomeric chain lengths of higher polydispersity, whereas in the lower temperature cure, oligomers of a smaller range of chain lengths are present.     

EVOH基梳型聚合物的合成和表征

以乙烯-乙烯醇共聚物(EVOH)为原料,在乙醇钠的催化作用下,通过与环氧乙烷(EO)的反应,合成出侧链为醚链结构且端基为羟基的梳型聚合物.采用红外光谱(IR)、核磁共振波谱(NMR)、凝胶渗透色谱(GPC)法对梳型聚合物的结构及其分子量进行了表征.讨论了EVOH与EO摩尔配比(r)和催化剂对接枝反应速度、接枝度、接枝长度、粗产率、分子量及其分子量分布的影响.结果表明:增加催化剂的用量有利于环氧乙烷的转化率提高,接枝反应速度明显增加;随着r的减少,EVOH的接枝度增加,侧链上接枝EO的数目逐渐变大,而产物的粗产率变化不大,均为35%左右.