硅酸及其鹽的研究 Ⅰ.硅酸聚合的速度和機制

1.在较广的pH范围内,测定了硅酸胶凝的速度。表示pH和胶凝时间对数关系的曲线,其形状常为N字形,有一最高点和一最低点,不论所用酸的种类如何。不同的酸使曲线的最高点和最低点以及两者之间线段的部位显有区别。 2.硅酸离子随着溶液中外加酸浓度的增高而逐步与氢离子结合:H_2SiO_4→H_3SiO_4→H_4SiO_4→H_5SiO_4~ 。硅酸由聚合而形成凝胶的作用,在酸方和在硷方的机构不同。在硷方是原硅酸与其一价阴离子的缩合作用,而在酸方则是原硅酸和其一价阳离子的聚合作用。 3.根据以上的机构,我们提出一个关系式可以说明硅酸的胶疑时间和pH的关系。     

硅酸胶凝过程的显微研究

本文用不同浓度的盐酸酸化单硅酸钠溶液。硅酸胶凝过程中亚微观结构的变化通过显微录象和扫描电镜进行观察。结果发现,在碱性溶液中硅酸的胶凝过程分成三步。     

硅酸及其盐的研究(ⅩⅥ)——硅酸胶凝作用中的离解常数

以HOAc和H₂SO₄为酸化剂,研究了不同SiO₂/Na₂O摩尔比的硅酸钠在酸化后胶凝时间和pH的关系.从“N”曲线的结构求得了硅酸在胶凝作用中的各级离解常数.     

硅酸及其盐的研究 Ⅴ.氟离子和硅酸的聚合作用

在較广的pH范围內,测定氟离子对硅酸(酸化的水玻璃和单硅酸鈉)胶凝作用的影响。在中性和微碱性溶液中,氟离子促进硅酸胶凝,而且这作用随所加氟离子数量而加大。在酸性溶液中,氟离子也有促凝作用,并随氟离子增多而增加。但只增加到一定限度,过此限度,促凝作用卽行減退。所生凝胶的离浆溶液合氟量亦已测定。在碱性溶液,氟离子全部在离浆液中,表示氟离子不参加凝胶的組成而仅起催化作用。在酸陸溶液,氟离子全部或大部分在凝胶內,这表示它不仅参与反应而且是产物的組成部分。根据以前所提硅酸聚合的机制,对所观測到的結果作初步的解释。     

硅酸及其盐的研究 ⅩⅩⅠ.三甲基硅烷化-气相色谱法测定单硅酸的离解常数

单硅酸的离解常数是表征其基本性质的重要数据,前人已有不少工作,但由于测定的方法和实验条件不同,所得数据很不一致。本实验室曾用“N’曲线法测得了单硅酸的各级离解常数,由于这些常数系在单硅酸到达多硅酸直至凝胶的过程中所测得,故和公认的单硅酸标准离解常数差别很大,只能称为胶凝离解常数。     

~(13)C NMR谱验证醋酸与硅羟基的作用

硅酸溶液有自聚作用,即从低聚硅酸→中聚硅酸→高聚硅酸→硅凝胶。将硅酸溶液的胶凝时间对溶液的 pH 作图,曲线呈“N”形,曲线的位置随酸化剂种类等不同而改变。“N”曲线最高点位置用强酸(Hcl、H_2SO_4、HNO_3)皆在 pH1.5—2.0;用中强酸(H_3PO_4)在2.5左右;用弱酸(CH_3COOH)在2.5—4.0之间。并且曲线最低点位置也随酸化剂不同而明显不同。由于在所试酸化剂中,醋酸的差别最大,多年来一直引     

五种新型双胆固醇类衍生物的合成及其胶凝行为

以具有氢键形成结构基础的甘氨酸和范德华作用堆积倾向的胆固醇作为结构单元,以直链脂肪二酸为连接臂,通过DCC缩合,设计、合成并表征了5种双胆固醇衍生物.根据连接臂所包含亚甲基个数的不同,将这些化合物依次表示为1,2,3,4,5.系统考察了这些化合物在25种常见溶剂中的胶凝行为,结果表明,连接臂长度对化合物胶凝能力影响显著.其中,化合物1可以胶凝11种所测试溶剂,且最低胶凝浓度均不超过1.0wt%,化合物2可以胶凝其中的17种溶剂,化合物3可以胶凝11种,连接臂更长的化合物4和5则只能胶凝2种或者4种有机溶剂.SEM观察表明,连接臂长度对胶凝剂分子的微观聚集形貌也有显著影响.此外,聚集体形貌还与溶剂本性有关.值得注意的是,化合物2,3,4,5对DMSO的胶凝行为和在其中的聚集行为均表现出有趣的奇偶效应,即2和4可使DMSO胶凝,而3和5则不能使该溶剂胶凝,此外,2和4在其DMSO凝胶中形成容易折断的条片状聚集体,而3和5则以球状聚集体从DMSO中析出.FTIR分析表明,相对于自由态,聚集态时2,3,4,5的酰胺键N?H、C=O的伸缩振动和N?H的弯曲振动峰所对应波数呈现出明显的奇偶效应(即波数随连接臂碳原子个数增...     

硅酸及其盐的研究(Ⅺ)——单硅酸胶凝作用的温度效应和活化能

用H₃PO₄、HAc和HCl为胶凝剂,在较广pH范围内,研究0°、20°、30°、40°、50°和70℃等不同温度对单硅酸胶凝作用的影响,并求出活化能。所得结果表明:活化能随胶凝剂的种类和硅酸溶液的pH不同而不同。但也发现硅酸浓度不同时,活化能也有所不同。若总盐浓度恒定,则活化能不变。用硅酸聚合理论的有关概念,对所得结果作了解释。     

含磷小分子有机胶凝剂的合成及其胶凝行为研究

将对苯二酚双磷酸酯与胆固醇、甘氨酸胆固醇酯以及氯甲酸胆固醇酯的乙二胺反应产物反应得到了3种含磷双胆固醇衍生物(分别记作 1, 2, 3), 考察了这些化合物对35种常见溶剂的胶凝能力. 发现1仅可使CHCl₃部分胶凝, 3除了可使正戊烷部分胶凝外, 还可使正己烷到正癸烷6种烷烃胶凝, 结构介于1和3之间的2则既可胶凝醇类溶剂(正戊醇到正癸醇), 又可胶凝烷烃类溶剂(正戊烷到正癸烷、环己烷), 呈现出对质子性溶剂和非质子性溶剂的双性胶凝能力. 结合凝胶形貌的扫描电镜分析结果, 可以认为胶凝剂结构上的微小变化会导致其在胶凝能力和聚集体形貌上的巨大差异. 利用红外光谱、X射线衍射等手段进一步探讨了胶凝剂分子在凝胶中的堆积方式和彼此之间的相互作用本质.     

钕铁硼速凝薄片中α-Fe析出临界冷却速度的估算

采用FMI-I-600-R-C型真空感应熔炼速凝炉制备了不同厚度的钕铁硼速凝薄片,并用螺旋测微器从中分别选取厚度为0.2,0.3,0.4,0.5,0.6和0.7 mm的速凝薄片,采用扫描电子显微镜对各个薄片进行微观组织和微区成分分析,发现厚度为0.2~0.4 mm的速凝薄片中没有α-Fe析出,而厚度超过0.4 mm的速凝薄片靠近自由面处均存在α-Fe,表明冷却速度沿着厚度方向是逐渐降低的。当厚度超过0.4 mm时,靠近自由面处的冷却速度过低而不能完全抑制α-Fe的生成,以0.4 mm厚速凝薄片为研究对象,结合热传导理论和凝固理论,应用数学解析法计算了α-Fe在钕铁硼速凝薄片中析出的临界冷却速度。     

用金胺O作荧光探针研究PVA-H_2O-DMSO体系的凝胶过程

<正> 它在可见光区发荧光,其荧光量子效率随环境的粘度不同有较明显的变化。这是由于其分子中的芳香基团与中心碳是单键连接,易于转动。当环境的粘度增加时,这种转动受到阻碍,因而分子吸收激发光能后,损失于这种转动的热能相对减少,荧光量子效率则相对     

A NOVEL EOR POLYMER (Ⅱ)——INVESTIGATION ON IN-SITU GELATION OF SMRF SYSTEM IN BEREA CORE

In-situ gelation of aqueous sulfomethylated resorcinol formaldehyde (SMRF) system inBerea core has been investigated. Two sets of displacement experiments were conducted with thissystem (containing 5% NaCl, 0. 036% CaCl_2. 2H_2O). The brine permeabilities of the coreswere reduced significantly from about 600 to 0.1 md. The in-situ gelation in Berea core occurreda little bit earlier than gelation anticipated from bulk test in the experiments. The gel time waseasier to control at initial pH between 6 and 8. During injection of SMRF system, the apparentviscosity was less than 1 mPa·s at 41℃.     

羟基聚丁二烯羟值测定新方法

本文建立了两个相关的∑Aa_i-B_2型凝胶化反应方程,含试样官能团数和重均官能度两个未知数.解联立方程,得到一元二次方程.通过测定该方程的系数,间接测得试样官能团数和重均官能度.该方法用于H_2O_2引发的羟基聚丁二烯羟值测定。其结果比目前国内外通用的经典酰化法高一倍以上.证明新的羟值数据是正确的.     

Thermoreversible gelation of blend of poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) in γ-butyrolactone solution

Thermoreversible gelation behavior of blend of poly(vinylidene fluoride) and poly(vinylidene fluoride-trifluoroethylene) in γ-butyrolactone solution was studied. Sol-gel transition temperature increased with the increase of polymer concentration, but was independent of the blend ratio of two polymers. An equation for gelation rate was derived, assuming that the gelation is a first-order reaction and that the gelation rate obeys an Arrhenius type. According to the equation, the growth index of gelation and supercooling temperature had a dominant effect on gelation rate. The growth index of gelation, which was calculated from the dependence of activation energy on the supercooling temperature in the isothermal gelation, varied with the blend ratio of two polymers. Growth index of gelation larger than 2 was obtained for the blend gels studied in this experiment. It may suggest that the multidimensional growth of gels occurs in such polymer blend solutions. X-ray diffraction and differential scanning calorimetry measurements showed existence of separate crystals due to each component of polymer in the blend gels. © 1996 John Wiley & Sons, Inc.     

酶凝干酪素物理凝胶化过程的有限元模拟

以酶凝干酪素的凝胶化过程为对象,利用有限元方法数值分析了在凝胶化过程中温度场的空间分布和时间演变规律.在此基础上,基于一阶的凝胶化动力学方程,数值模拟了凝胶体系的复剪切模量场,进而分析了材料配方、体系尺寸与冷却方案对复剪切模量场的影响规律.模拟结果表明,由于热阻的差异,体系表面的冷却速率大于内部,表面首先发生凝胶化;而由于预凝胶化阶段的平均冷却速率决定了无穷复剪切模量的值,最终体系内部的复剪切模量超过表面的.     

Nanofibrosis of uncrystallizable poly(lactide‐co‐glycolide) via phase separation

Poly(lactide‐co‐glycolide) (PLGA) copolymers are a kind of biocompatible and biodegradable materials being widely used in tissue engineering. However, phase separation had not been reported successfully in fabricating these amorphous polymers into nanofibrous matrix, although this technique had shown advantages over electrospinning in producing a nanofiber network. In this study, tetrahydrofuran (THF)/H₂O solvent pairs were found suitable solvents to induce the formation of uniform PLGA gel at selected gelation temperatures. The results indicated that fine nanofibrous structures with fiber diameter around 40–60 nm could be obtained following the steps of gel formation, solvent extraction, and freeze‐drying, by controlling the concentration of PLGA/THF/H₂O solution, THF/H₂O ratio, and gelation temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Role of urea in the preparation of highly porous nanocomposite aerogels

The preparation of highly porous CoFe2O4-SiO2 nanocomposite aerogels was successfully achieved by a novel sol-gel procedure involving urea-assisted co-gelation of the precursor phases. This method allows fast gelation, giving rise to an aerogel with 97% porosity. The formation of CoFe2O4 nanocrystals homogeneously distributed within the matrix occurs after calcination at 750 degrees C and is complete at 900 degrees C. Despite the high temperature required for the formation of the CoFe2O4 nanocrystals, the high porosity typical of aerogels is still retained.     

凝胶化反应全过程的激光光散射跟踪研究

在苯乙烯（Ｓｔ） 二乙烯苯（ＤＶＢ）自由基共聚的凝胶化反应过程中定时取样，得到凝胶化点前后及至终点的一系列样品，然后用激光光散射技术，包括研究散射光强及其角度依赖性的静态光散射（ＳＬＳ）和研究散射光频移的动态光散射（ＤＬＳ），表征了这系列样品的重均分子量Ｍｗ、均方旋转半径Ｒｇ、第二维利系数Ａ２及流体力学半径Ｒｈ等静、动态参量及这些参量的变化规律，定量地描述了凝胶化反应全过程     

聚丙烯酰胺稀溶液的粘度与剪切速率的关系的研究

聚丙烯酰胺稀溶液的粘度与剪切速率的关系的研究陈九顺，刘忠义，刘波，张艳红（黑龙江大学化学系，哈尔滨，１５００８０）关键词聚丙烯酰胺，部分水解聚丙烯酰胺，粘度，剪切速率水溶性高聚物聚丙烯酰胺（ＰＡＭ）和部分水解聚丙烯酰胺（ＰＨＰ）的水溶液是一种假塑性流...     

INFLUENCE OF ALCOHOL-BASED NONSOLVENTS ON THE FORMATION AND MORPHOLOGY OF PVDF MEMBRANES IN PHASE INVERSION PROCESS

Through the preparation of PVDF membranes using various nonsolvent coagulation baths following the phase inversion process, the influence of alcohol-based nonsolvents on the formation and structure of PVDF membranes were investigated. The light scattering and light transmission measurements were used to characterize the equilibrium phase diagram and the gelation speed, respectively. The locations of the crystallization-induced gelation boundaries for various systems and precipitation processes were explained from the corresponding thermodynamic and kinetic parameters. It was found that the better affinity between alcohol-based nonsolvents and DMAc solvent caused the gelation boundaries further away from the PVDF-DMAc axis with the coagulation bath varying from water, methanol, ethanol to iso-propanol. Due to the lower exchange rate of DMAc and alcohols, the delayed demixing took place for the membrane-forming using alcohols as baths, and the delayed time became longer when the coagulation bath was changed from methanol, ethanol to iso-propanol. The characterization results of membranes indicate that the influence of nonsolvents on the phase diagram and the precipitation process are in agreement with those on the membrane morphology. The better thermodynamic stability and a low exchange diffusion rate of PVDF/DMAc/alcohols favor the liquid-solid phase separation in gelation process, and therefore yield the membranes with a porous upper surface, a particular bottom surface and symmetrical structure.