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111.
An enzymatic treatment with cellulases fromTrichoderma viride was investigated in its effect on the pore structure of different types of bead cellulose. One objective of this study was to establish a suitable procedure for combined enzymatic treatment and solvent exchange that would restore the original pore structure which the beads had before drying without causing major losses in mechanical stability. Another aim was to further increase the accessible pore space and internal surface area for separation of large molecular weight compounds with regard to Chromatographic applications. Finally, an attempt was made to extend the findings for unsubstituted beads to the derivatives carboxymethyl (CM) and diethylaminoethyl (DEAE) cellulose beads. The enzymatically treated samples were characterized by microscopic methods and porosity measurements such as mercury porosimetry, nitrogen sorption and size exclusion chromatography. It was found that under controlled conditions the low-porosity surface layer of dried beads could be removed making the internal pore space accessible without reducing the resistance to deformation of the beads. Additionally, a shift in pore size distribution towards larger pores was observed. Supplementary swelling treatments in solvents of high swelling power could substantially restore the former porosity of the dried beads but did not enhance the accessibility to the cellulases to a considerable extent. Internal pore volume and surface area of the derivatives were dramatically increased in the case of DEAE upon enzymatic hydrolysis, however, at the expense of mechanical stability, whereas CM was found to be less affected. 相似文献
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114.
A large number of experimental results of different surfactant adsorption systems (mainly on the silicas) obtained from both equilibrium and kinetic studies under different conditions are interpreted by a model of small individual surface aggregates. The adsorption model is contrasted with the influences of various factors, including electrostatic interaction, hydrophobic interaction, concentrations, types of coions, types of counterions, surfactant structure, alkyl chain length, types of head groups, neutral electrolytes, pH, adsorbent structure, porosity, surface charge density, and surface polarity.Dedicated to Frau Professor Dr. Elsa Ullmann on the occasion of her 80th birthday 相似文献
115.
Weiwei He Louise M. A. Jakobsen Line F. Zachariassen Axel K. Hansen Henrik J. Andersen Hanne Christine Bertram 《Magnetic resonance in chemistry : MRC》2022,60(7):651-658
Currently, the existence of a gut–bone axis receives massive attention, and while sound premises and indirect proofs exist for the gut–bone axis concept, few studies have provided actual data linking the gut and bone physically. This study aimed to exploit the versatile nature of nuclear magnetic resonance (NMR) to link NMR relaxometry data on bone mineralization with NMR spectroscopic profiling of gut metabolites. For this purpose, sample material was obtained from a 6-week intervention study with ovariectomized (OVX) rats (n = 49) fed with seven different diets varying in calcium content (0.2–6.0 mg/kg) and prebiotic fiber content (0–5.0% w/w). This design ensured a span in (i) calcium available for bone mineralization and (ii) metabolic activity in the gut. After termination of the intervention, longitudinal (T1), transverse (T2) relaxation, and mechanical bone strength were measured on the excised femur bones. A PLS model with high predictability (Q2 = 0.86, R2 = 0.997) was demonstrated between T2 decay curves and femur mechanical strength. Correlations were established between bone T2 populations and gut short-chain fatty acids. In conclusion, the present dual NMR approach showed strong correlation between T2 relaxation and mechanical strength of the bone, and when metabolic activity in the gut was modulated by inulin, the potential existence of a gut–bone axis was demonstrated. 相似文献
116.
Porosity of porous Al alloys 总被引:12,自引:0,他引:12
Two porosity models of porous Al alloys with different pore types (ball and polygon shape) were established. The experimental results coincide well with theoretical computations. The porosity of Al alloys (Prc) consists of three parts, porosity caused by preform particles (Prp), additional porosity (Pra), and porosity caused by solidification shrinkage (Prs). Prp is the main part of Prc while Pra is the key for fabricating porous Al alloys successfully in spite of its little contribution to Prc. 相似文献
117.
锐钛矿型多孔TiO2薄膜的溶解法制备及性能表征 总被引:2,自引:0,他引:2
在具有锐钛矿晶粒的TiO2溶胶中加入苯丙乳液粒子,使用该混合液浸渍提拉涂膜,然后利用甲苯将薄膜中的苯丙乳液粒子溶解去除,并通过重复涂膜,在室温下获得了具有良好多孔性的锐钛矿型TiO2薄膜。考察了多孔薄膜的表面形貌、光学性能、吸附性能和光催化性能。结果表明:随薄膜涂膜次数的增加,TiO2多孔薄膜的吸光度增大,透光率减小,光吸收边波长向长波方向移动。罗丹明B在TiO2多孔薄膜上的吸附量随涂膜次数的增加先升高,后降低;多次涂膜会在薄膜中产生半封闭的孔洞,经过长时间的毛细渗透等作用能进一步增加薄膜对罗丹明B的吸附。TiO2多孔薄膜通过吸附+光催化氧化的模式快速分解罗丹明B,其活性主要受到薄膜在光催化反应初期的吸附能力的影响。此外,TiO2的负载量、光的利用效率、以及光生电荷迁移及其分离等也是影响薄膜光催化活性的因素。 相似文献
118.
Matsuda Atsunori Matsuno Yoshihiro Tatsumisago Masahiro Minami Tsutomu 《Journal of Sol-Gel Science and Technology》2001,20(2):129-134
Porous silica films were obtained by a heat treatment of poly(ethyleneglycol)-containing gels for micro-patterning. Changes in porosity and the amount of adsorbed water with the heat treatment temperature in the silica films were evaluated from the refractive index of the films. The apparent refractive index of the silica films in an ambient atmosphere was much higher than the intrinsic refractive index of the film due to the large amount of adsorbed water in the films. The amount of adsorbed water in the films decreased with an increase in the heat treatment temperature and became almost zero after a heat treatment at 850°C. The decrease in the amount of adsorbed water in the films was caused by the decrease in silanol groups, which acted as the sites for water adsorption in the films. The drastic decreases in thickness and in porosity of the films at temperatures from 850 to 950°C occurred after the disappearance of silanol groups in the films. The densification of the films due to collapse of the pores at high temperatures should have resulted from the viscous flow of silica network. 相似文献
119.
Jiugui Liu Lizhong Jiang Jiayu Zhan Dezhen Wu Riguang Jin 《Frontiers of Chemistry in China》2007,2(1):13-16
A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane
(PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU
films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy
and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal
treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the
size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the
existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass
fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the
decrease of tensile strength and the rise of water absorption.
Translated from Chemistry Journal of Chinese Universities 2006, 27(1): (in Chinese) 相似文献
120.
焦化过程半焦孔隙结构时空变化规律的实验研究——孔隙率、比表面积、孔径分布的变化 总被引:6,自引:1,他引:6
以井式加热炉(φ150mm×300mm) 为主体模拟工业炼焦过程,借助压汞法考察了焦化过程中不同焦化温度、炉内径向不同位置半焦的孔隙结构参数的变化。结果表明,半焦中存在丰富的大孔和中孔,孔隙率和比表面积随焦化温度、径向位置呈规律性变化;相同焦化温度下,由边缘沿中心方向先减少后增加;相同位置下,孔隙率随着温度的升高逐渐变小,至900℃后孔隙率略有增大,比表面积在900℃左右达到最小值后随温度升高又迅速增加;此外,半焦孔隙以孔径大于5.0μm的孔为主,孔径小于0.4μm、介于0.4μm~5.0μm和大于5.0μm的孔累积孔隙分率分别约占总孔体积分数的10%、20%和70%,孔径分布的高峰处于60 μm~150μm。SEM分析显示,焦柱中存在丰富的大孔,且边缘和中心处孔径较大。 相似文献