Surface-initiated atom transfer radical polymerization of methyl methacrylate on magnetite nanoparticles

The synthesis of magnetite nanoparticles coated with a well-defined graft polymer is reported. The magnetite nanoparticles with an initiator group for copper-mediated atom transfer radical polymerization (ATRP), 2-(4-chlorosulfonylphenyl) ethyltrichlorosilane (CTCS) chemically bound on their surfaces were prepared by the self-assembled monolayer-deposition method. The surface-initiated ATRP of methyl methacrylate (MMA) was carried out with the CTCS-coated magnetite nanoparticles in the presence of free (sacrificing) initiator, p-toluenesulfonyl chloride. Polymerization proceeded in a living fashion, exhibiting first-order kinetics of monomer consumption and a proportional relationship between molecular weight of the graft polymer and monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.7 chains/nm². The molecular weight and polydispersity of the graft polymer were nearly equal to those of the free polymer produced in the solution, meaning that the free polymer is a good measure of the characteristics of the graft polymer. The graft polymer possessed exceptionally high stability and remarkably improved dispersibility of the magnetite nanoparticles in organic solvent.     

常德发酵米粉中的微生物分离纯化与鉴定

本文对常德发酵米粉中的微生物进行了分离纯化,并用试剂盒对其进行了鉴定.鉴定结果为胚芽乳杆菌（Lactobacillus plantaum）等十二株乳酸杆菌,鸟链球菌（Enterococcus avium）等五株乳酸链球菌,酿酒酵母（Saccharomyces cervisiae）等九株酵母菌.     

Optically detected cyclotron resonance in semiconductors

In high quality semiconductor crystals, occurrence of cyclotron resonance is beautifully reflected on luminescence spectra. This feature is demonstrated in typical elemental semiconductor Ge, both doped and undoped. One obtains new information of kinetics in free carriers, free excitons, bound excitons and electron-hole drops.     

Schiff's bases of polyallylamine

Summary Schiffs bases of polyallylamine were synthesized by the reaction with four aldehydes. Salicylaldehyde (S)- and 2-pyridinecarboxaldehyde (P)-Schiff's base could be used as reverse osmosis membranes when crosslinked with divinyl sulfone, diacetyl or ethylene glycol diglycidyl ether. S-base membrane had a high mechanical strength but poor water permeability (K₁), while P-base membrane showed a high rejection, particularly against CoCl₂, and a high K₁ because of chlate formation, but poor strength. The membranes of P-base and a hybrid PS-base exhibited a possibility of separating alkali metal salts and transition metal salts from each other.     

Properties of poly(4-vinylpyridine-co-methyl vinyl ketone) membranes for reverse osmosis

The copolymer prepared from 4-vinylpyridine and methyl vinyl ketone could form a dense and tough membrane which is stronger than cellulose acetate when crosslinked with malonyl dihydrazide (MD) or 2-phenyl-4,6-dihydrazino-s-triazine (PDT), showing a fair performance in reverse osmosis for NaCl and CoCl₂ feed. The relationship between the content of MD or PDT and the membrane performance was investigated. An increase in MD or PDT led to an increase in membrane thickness and water content as well as the performance. A maximum rejection was obtained at ca. 30 mol % MD and ca. 13 mol % PDT based on MVK, and a maximum membrane strength at 20–30 mol % crosslinking agent. A membrane of a lower NaCl rejection tended to be permselective due to the complexation of the CoCl₂ with membrane. About 1:1 copolymer gave membranes of a higher rejection, which may be related to monomer arrangement in the copolymer chain. There methods for the flux improvement were presented and discussed: preparation of a copolymer blend membrane containing a hydrophilic monomer, crosslinking quaternization of membranes with diiodobutane, and oximation of the membrane material in order to introduce hydrophilic groups.     

Rates of gas absorption with interfacial turbulence caused by micro-stirrers

Rates of absorption of CO₂ into water, a 0.2 mol/L NaOH solution and a 40 wt% glycerol solution with and without the interfacial turbulence caused by micro-stirrers, made of a magnetic material, were measured with use of a stirred vessel with known gas-liquid interfacial area. The effect of the interfacial turbulence on the rate of gas absorption was remarkable in the lower range of the bulk turbulence. The enhancement factors due to the interfacial turbulence were calculated with use of the age distribution function of the Danckwerts type and they agreed well with the experimental results.     

Gas absorption with consecutive chemical reaction: Absorption of carbon dioxide into aqueous amine solutions

Experiments were carried out over a wide range of contact time for the absorption of carbon dioxide into aqueous amine solutions. It was suggested from the experimental results with a laminar liquid-jet, a wetted wall column and a quiescent liquid absorber that the present absorption processes should be analyzed by a gas absorption with the consecutive reaction of the form of A + 2B →k_I R and A + R →k_II Products. The values of rate constants for the second-order first reaction step (k₁) for the diethanolamine and triethanolamine were estimated as 1340 and 16.8 1/mol-sec, respectively. The value of rate constant for the second reaction step was found to be constant irrespective of the liquid reactant.     

Properties of reverse osmosis membranes prepared from poly(4-vinyl pyridine)-acrylonitrile copolymer and the partially quaternized copolymer

Reverse osmosis membranes were prepared from 4-vinyl pyridine(4VP)-acrylonitrile (AN) copolymers and those partially quaternized. Their salt rejection (S) and hydraulic water permeability (K₁) were investigated with regard, to co-polymer composition, the membrane profile by SEM observation, cross-linking quaternization with diiodobutane (DIB) and the method of membrane preparation. S decreased with increasing AN content, but K₁ was closely dependent on water content which had a minimum at about 65% 4VP. The increase in K₁ and water content in a high AN range was caused by the change in the membrane structure from dense to porous one.Quaternization with DIB to a small extent notably improved K₁, up to ten times without significant change in S, and most effectively improved both of the membrane structure and the performance of AN rich copolymer membranes which were the highest in tensile strength among the copolymers. It was found by IR and elemental analysis that DIB charged was nearly completely reacted. The DIB modified membranes were anion exchangeable and more than two-thirds of iodide were exchanged for chloride. The modification reduced the membrane strength, to the least extent in the AN rich copolymers, with increasing DIB due to an increase in water content. The quaternized membranes prepared by surface-treating with DIB gave an essentially similar performance and had a composite structure which held unreacted layer.Monofunctional quaternizing agents merely brought about a poor membrane performance.Water transport through the membranes followed solution-diffusion mechanism for the membranes of volume fraction of water smaller than 0.41. The membranes modified with DIB to a small degree were regarded as tight ionic membranes and able to be treated as a nonionic ones, although they behaved ionically showing a decrease in S with the increasing feed concentration.     

干法糊化对燕麦粉面团应力松弛特性的影响

采用挤压、蒸汽、微波及烘烤4种干法处理燕麦籽粒或燕麦粉,测定不同处理及不同糊化度燕麦粉面团的应力松弛特性。结果表明:挤压、蒸汽、微波及烘烤处理的燕麦粉糊化度分别为77.8%、39.3%、17.8%及13.7%。相对于其他糊化方法,挤压处理组面团的松弛时间、阻尼系数、残余应力最大,分别为60.90 s、3.70×10~6N·m~(-2)·s、9.39×104N·m-2;糊化度与燕麦粉面团的松弛时间、阻尼系数、残余应力均显著正相关(R=0.97、0.99、0.99;P0.05)。干法糊化显著提高了燕麦粉面团的黏性和结合力。     

电生功能水用于提高鲜切马铃薯产品品质的试验研究

对电生功能水杀灭鲜切马铃薯表面微生物以及抑制马铃薯切片氧化褐变的效果进行了研究。用电生功能水及自来水分别处理经过大肠杆菌O78，金黄色葡萄球菌26003，枯草芽胞杆菌1．1849三种微生物接种的马铃薯切片，对处理后其微生物指标进行了观察。试验发现采用普通自来水浸泡清洗并不能有效的降低样品的微生物指标，而用指标为pH2．5、ORP1180mV、ACC35mg／L的电生功能水处理鲜切果蔬产品，可以明显的降低附着于产品上的各类微生物。通过考察电生功能水浸泡处理对马铃薯切片表面色泽的影响，确认了电生功能水抑制其氧化褐变的效果，实验证明，电生功能水具有与常用褐变抑制剂L-半胱氨酸 柠檬酸等同的抗褐变效果。对提取到的马铃薯多酚氧化酶进行酶活钝化实验发现，电生功能水可以使马铃薯PPO活性降低50％以上，与L-半胱氨酸 柠檬酸对马铃薯PPO活性的抑制能力相当，说明电生功能水能有效的钝化果蔬组织中多酚氧化酶的活性而抑制果蔬切片氧化褐变的发生。试验结果证明：电生功能水处理可以有效杀灭附着于鲜切马铃薯表面的各种微生物，并可以较好的抑制鲜切马铃薯氧化褐变的发生，增加了产品的食用安全性，提高了产品的品质。