凝胶条件对PVDF／PVC中空纤维膜性能及结构的影响

采用干-湿相转化法制备PVDF/PVC共混中空纤维膜,通过对水通量、孔隙率、平均孔径的测试及扫描电镜的微观分析,讨论了凝胶浴组成、温度和芯液浓度对PVDF/PVC中空纤维膜性能及结构的影响,并进行了详细的理论分析.试验结果表明,提高凝胶浴温度和浓度有利于增加膜的水通量,但对孔隙率有一定的影响,在芯液中加入一些溶剂是提高通量的一种手段.但加入量要合理.     

制膜工艺条件对PVC/SPES共混膜性能的影响

采用溶剂-非溶剂扩散致相分离的方法,在不同制膜条件下(铸膜液聚合物含量、铸膜液温度、凝胶浴温度和凝胶浴组成)制备了PVC/SPES共混膜,并对膜的纯水通量、截留率、断裂强度、耐污染性能和膜的断面结构等性能进行了测试,从而探讨制膜工艺条件对PVC/SPES共混膜微观结构及性能的影响.通过对不同聚合物含量的共混膜的纯水通量、截留率、机械性能和耐污染性能测试比较,得到PVC/SPES共混膜的最佳制膜条件:聚合物质量分数为16％,铸膜液温度为70℃,凝胶浴温度为20℃,凝胶浴为纯水.     

PVDF/CA共混微滤膜的研制

通过PVDF与CA共混来提高PVDF膜的亲水性,以纯水通量、膜的最大泡点压力、平均泡点压力等性能为指标,设计了九因素(共混比、固含量、溶剂种类、溶剂比、添加剂种类及含量、蒸发时间、凝胶浴温度、凝胶时间)四水平的正交试验表研究膜制备过程中各因素对PVDF/CA共混微滤膜性能的影响.实验结果表明:固含量是最主要的影响因素,其次是共混比、溶剂种类、添加剂含量、凝胶浴温度、凝胶时间、蒸发时间、添加剂种类和溶剂比.较佳的成膜条件为:PVDF/CA共混比4∶1,固含量12%~14%,添加剂N-甲基-2-吡咯烷酮质量分数2%~3%,二甲基甲酰胺/正丁醇混合溶剂比7∶1,蒸发时间30 s,在20~30℃的自来水中凝胶50~70 min.在此较优条件下可制备孔径为0.55~0.65μm,0.06 MPa下的纯水通量27℃时为205.37~292.53 mL/(cm2.h)的PVDF/CA共混微滤膜.     

PVDF/PVA共混膜的研究

采用湿法相转化法制备了聚偏氟乙烯(PVDF)/聚乙烯醇(PVA)共混膜,研究了PVDF/PVA共混体系的相容性,并讨论了PVDF/PVA共混比、固含量、添加剂浓度、凝固条件与后处理对膜结构及性能的影响.结果表明,PVDF/PVA为不相容体系,在成膜过程中产生界面微孔;随PVA含量增加,PVDF/PVA共混膜水通量先增大后减小,在PVDF/PVA为8/2时呈较大值,截留率变化趋势则相反;PVA的存在明显改善了PVDF/PVA共混膜的亲水性,表现为随其含量增加共混膜接触角明显减小;随固含量增加,膜厚度增加,孔隙率降低,水通量减小,截留率升高;添加剂PEG600浓度为6%时,孔隙率高,水通量大,但截留率低;凝固浴种类直接影响膜结构及性能;热处理可完善膜结构从而获得性能更优的膜.选择适当的铸膜条件可制成较好的膜产品,而且共混膜通量明显大于各组分通量的加权,表明共混是一种改善PVDF膜性能的有效方法.     

两步法制备醋酸纤维素微滤膜的研究

以二醋酸纤维素酯为制膜材料，以DMF／丙酮为混合溶剂体系，采用两步法制备微滤膜，第一步在水蒸气气氛中吸湿并挥发溶剂而分相凝胶，第二步浸入水中固化制膜．研究了聚合物浓度、溶剂比例、添加剂含量、吸湿时间等因素对膜性能的影响，制备了孔径约0．5μm的微孔滤膜，其性能指标可基本达到商业膜的标准．     

PVDF/EVOH共混膜制备及其抗污染特性的分析

用相转化法对聚偏氟乙烯(PVDF)超滤膜进行了乙烯-乙烯醇共聚物(EVOH)共混改性,系统考察PVDF/EVOH共混比和凝胶浴温度对共混膜性能的影响.并使用原子力显微镜(AFM)胶体探针定量测定了共混改性前后,亲/疏水性污染物与膜之间作用力的变化特点,结合宏观过滤实验解析添加EVOH对PVDF抗污染性能的影响.结果表明:PVDF/EVOH相容性最佳的共混比为9∶1.与纯PVDF膜相比,PVDF/EVOH共混膜的亲水性明显提高.共混膜的亲水性及拉伸强度随着凝胶浴温度的增大而增大,但是纯水通量随着凝胶浴温度的增大而减小.主要是因为高凝胶浴条件下膜表面有致密的皮层形成.膜-污染物间作用力及污染试验表明,添加EVOH后有效降低了膜-污染物间的相互作用力及相应的膜污染速率,表明了EVOH的引入能有效改善了膜的抗污染性.     

CA/PSf共混超滤膜的制备及性能研究

以聚砜(PSf)为基膜材料,醋酸纤维素(CA)为共混膜材料,N,N-二甲基乙酰胺(DMAc)为溶剂,去离子水为凝固浴,采用非溶剂致相分离法(NIPS法)制备CA/PSf共混平板超滤膜.综合考察了共混膜有机物溶出量,铸膜液聚合物浓度和共混比以及不同凝固浴组成对膜结构、水通量、水接触角、孔隙率、蛋白质截留率的影响.结果表明:相对于传统的以聚乙烯吡咯烷酮(PVP)作为添加剂的共混膜,使用CA作为添加剂,共混膜有机物溶出量大幅降低.随着CA含量的增加,共混膜孔隙率逐渐增大,亲水性增加.另外,随着凝胶浴中溶剂含量的增大,共混膜纯水通量不断降低,BSA截留率逐渐升高,膜形态结构变得更加致密.     

利用非溶剂诱导相分离法制备低介电常数聚酰亚胺微孔薄膜EI北大核心CSCD

利用非溶剂诱导相分离法,制备了一种低介电常数聚酰亚胺(PI)微孔薄膜。扫描电镜观察表明,聚酰亚胺微孔薄膜中泡孔均匀,其平均孔径在6~28μm之间。随着聚酰胺酸(PAA)浓度的增大及凝固浴温度的升高,所制得的聚酰亚胺微孔薄膜的孔隙率和平均孔径均增大。介电性能分析表明,聚酰亚胺微孔薄膜的介电常数明显下降,当孔隙率为80%时,聚酰亚胺微孔膜的介电常数(1 MHz)为1.81。拉伸性能测试表明,随着孔隙率增加,聚酰亚胺微孔膜的拉伸强度和拉伸模量均逐渐下降,但断裂伸长率增大。     

利用非溶剂诱导相分离法制备低介电常数聚酰亚胺微孔薄膜

利用非溶剂诱导相分离法,制备了一种低介电常数聚酰亚胺(PI)微孔薄膜。扫描电镜观察表明,聚酰亚胺微孔薄膜中泡孔均匀,其平均孔径在6~28μm之间。随着聚酰胺酸(PAA)浓度的增大及凝固浴温度的升高,所制得的聚酰亚胺微孔薄膜的孔隙率和平均孔径均增大。介电性能分析表明,聚酰亚胺微孔薄膜的介电常数明显下降,当孔隙率为80%时,聚酰亚胺微孔膜的介电常数(1 MHz)为1.81。拉伸性能测试表明,随着孔隙率增加,聚酰亚胺微孔膜的拉伸强度和拉伸模量均逐渐下降,但断裂伸长率增大。     

PVDF/PMMA/CA共混膜的制备及性能研究

主要讨论了PVDF(聚偏氟乙烯)／PMMA(聚甲基丙烯酸甲酯)／CA(醋酸纤维素)三元共混膜的制备及性能,并研究了影响膜性能的主要因素．正交实验结果表明：在PVDF／PMMA／CA体系中,PVDF同亲水性物质PMMA和CA的共混比是影响共混膜的水通量的首要因素;而PMMA与CA的共混比则对共混膜强度影响最大,当PMMA与CA的质量共混比为1：1时,膜强度最大;PMMA对膜的亲水性有较大的贡献,共混膜中只要有PMMA加入,其润湿角就变得同纯PMMA膜的润湿角相接近,通过采用红外衰减全反射法和干膜撕裂法,分别从微观和宏观上证明了PVDF／PMMA/CA气制膜体系在自来水中将会发生分层凝胶现象;综合考虑膜的各种性能,针对PVDF／PMMA／CA体系,较佳的制膜条件定为A883C2D12,也就是PVDF/CA/PMMA的质量共混比为12：2：1,以质量溶剂比为8：2的二甲基甲酰胺(DMF)／冰乙酸混合溶剂溶解,制得的膜的性能较好．     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.