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.     

聚偏氟乙烯凝胶电解质组成间相互作用及其凝胶化研究

通过冷却聚偏氟乙烯 (PVDF) 丙烯碳酸酯 (PC)或PVDF PC LiClO4的溶液 ,制备了数个聚合物凝胶 .实验表明 ,聚合物凝胶的凝胶化时间 (tgel)与凝胶温度、聚合物浓度有关 ,且强烈地依赖于体系中盐的浓度 ,因为盐会缩短体系的tgel.凝胶体系中LiClO4的存在提高了其凝胶熔融温度 (Tgm) ,LiClO4的含量越大 ,相应凝胶的Tgm 越高 .用DSC和落球法所测凝胶的Tgm 有较大的差别 .这说明凝胶中可能存在热稳定性好和热稳定性相对较差的两种不同结构部分 .FT IR的研究结果表明 ,凝胶电解质的各组成 (LiClO4,PC和PVDF)间存在较强的相互作用 .对含盐和不含盐的两类凝胶体系的对比研究表明 ,两者不同的凝胶化现象和Tgm 归因于盐与聚合物或溶剂间的络合作用     

聚丙烯酰胺凝胶结构非均匀性的动态光散射研究

利用动态光散射技术研究了聚丙烯酰胺 (PAAm)凝胶结构的非均匀性 ,分析了PAAm凝胶结构非均匀性的形成原因及凝胶动态光散射的数据处理方法和分析结果的物理意义 .研究结果表明 ,PAAm凝胶中含有动态相关长度 (LC)不同的两相 ,其中 ,LC 为 10～ 2 0nm的区域是聚合物稀疏相 ,LC 为 85nm左右的区域是聚合物密集相 ,两相的不均匀分布形成了PAAm凝胶结构的非均匀性 .分析表明 ,PAAm凝胶存在两相主要是由于单体和交联剂的溶解度存在差异所致 .随交联度增大 ,PAAm凝胶结构的非均匀性显著增强     

自由基引发的凝胶化反应的Monte Carlo模拟

基于自由基凝胶化反应的基本原理,在一个具有周期性边界条件的二维网络上,利用动态ＭｏｎｔｅＣａｒｌｏ 方法模拟了聚合物凝胶的自由基凝胶化反应,得到了凝胶的具体结构,研究了总单体浓度（ 单体浓度和交联剂浓度之和） 对凝胶的分形结构和孔径分布的影响．模拟中首次考虑了聚合后单体的运动对凝胶结构的影响．结果表明：考虑聚合后单体的运动,可使所得凝胶网络的分形维数和凝胶化所需的最低浓度均显著小于动力学凝胶化模型和ＤＬＡ 模型的相应值．用移动气泡法得到了凝胶网络的孔径分布,发现凝胶网络中大孔所占百分率明显多于随机纤维网络模型．     

聚丙烯酰胺与Cr(Ⅲ)低聚物交联机理的研究

采用分离Cr(Ⅲ )低聚物 ,分别考察其与聚丙烯酰胺反应活性的方法 ,研究了Cr(Ⅲ )低聚物与部分水解的聚丙烯酰胺交联机理 .用离子交换色谱法分离Cr(Ⅲ )低聚物得到纯的单体、二聚体和三聚体 ,经紫外、氧化还原滴定和离子色谱法确定了它们的结构 ,分别用它们与部分水解的聚丙烯酰胺交联反应 .在pH =6～ 12 ,聚合物浓度在 30 0～ 10 0 0mg L ,交联剂Cr(Ⅲ )浓度在 2～ 2 5mg L的范围 ,对成胶因素进行对比研究 .实验结果发现二聚体成胶的pH范围宽 ,用量少 ,三聚体次之 ,单体最差 .说明Cr(Ⅲ )低聚物是成胶反应的决定步骤 ,二聚体的反应活性最高 .从而完善地阐述了Cr(Ⅲ )离子与聚丙烯酰胺交联反应的机理     

部分水解聚丙烯酰胺弱凝胶交联动力学的流变学分析

用流变学方法对部分水解聚丙烯酰胺(HPAM)苯酚甲醛间苯二酚交联体系的弱凝胶化过程进行了研究,通过对基团转化率和高分子交联转化率的分析,发现凝胶化过程在接近凝胶点时,处于反应动力学的初期,这使得交联点增加的动力学是比较简单的.通过在不同聚合物浓度和交联剂浓度并在地层温度和矿化度条件下线性粘弹性行为的研究,得到了交联体系凝胶化动力学过程的完整数据,发现聚合物浓度与交联剂浓度对凝胶点与凝胶强度的影响比较类似,反映出交联点增加的共同动力学特征.复数粘度在一个诱导期后,是以指数上升的,类似一个一级反应的特征.产生交联的临界聚合物浓度约为250mg L左右.并提出了剪切粘度数学模型,可以描述凝胶化过程中流变性质的变化.     

The delayed crosslinking amphiphilic polymer gel system based on multiple emulsion for in-depth profile control

Delayed crosslinking polymer gel systems are widely used in-depth profile control technology for water production control. In this paper, an amphiphilic polymer P(AM-NaA-DDAM) was synthesized by a free radical micellar polymerization method and a delayed crosslinking amphiphilic polymer gel system was prepared based on multiple emulsion of W₁/O/W₂ emulsion which was prepared by a two-step emulsification method. The optimized formulation of amphiphilic polymer gel systems is: 0.15% P(AM-NaA-DDAM), 0.3% methenamine, 0.02% resorcinol, and 0.3% citric acid. The delayed gelation time of the delayed crosslinking amphiphilic polymer gel system is closely related to the stability of the W₁/O emulsion. By using multiple emulsion delayed crosslinking method, the delayed crosslinking amphiphilic polymer gel system with diesel as the oil phase can delay the gelation time up to 168 hours.     

添加剂对PVDF相转化过程及膜孔结构的影响

研究了PVP、PEG及LiCl 3种成孔添加剂下PVDF DMAc H2 O 添加剂体系的成膜机理 .无论那种添加剂的铸膜液相转换成膜过程中都存在凝胶分相和液液分相两种相变方式 ,在 30～ 6 0℃时凝胶分相在较低的非溶剂浓度下先于液液分相发生 ,LiCl作为添加剂较PEG、PVP对铸膜液有较强的致凝胶作用 ,成膜过程中凝胶分相段时间依PVP、PEG、LiCl的顺序延长 ,导致液液分相初始分相点处聚合物浓度增大 ,阻止了大孔结构的充分发展 .制得的膜依PVP、PEG、LiCl的顺序有效孔隙率和通量降低 ,结晶度升高 .以LiCl为添加剂制得的膜几乎不改变PVDF膜的疏水性 ,而以PVP或PEG为添加剂的膜隔水压差降低约 2 0kPa .     

水溶性高分子弱凝胶体系凝胶化过程的Monte Carlo模拟

为研究弱凝胶的形成过程,并把高分子弱凝胶用于三次采油,采用三维Monte Carlo模拟了高分子溶液凝胶化过程. 模拟预测了凝胶化开始的时间,得到了凝胶化过程中分子量分布的演化规律和胶团生长的三维图像. 发现生成溶胶与凝胶团的歧化过程,初始聚合物的浓度对能否形成凝胶至关重要,低于临界浓度不能形成凝胶. 模拟了凝胶化速度和聚合物浓度以及交联剂浓度的关系,并与粘度随凝胶化时间变化的实验结果进行比较, 结果表明, 聚合物浓度较高时,浓度对交联反应的影响减弱,这一趋势与实验结果相一致.     

THE MECHANISM OF COPOLYMERIZATION OF VINYL AND DIVINYL MONOMER Ⅵ: A STUDY ON THE MECHANISM OF THE STRUCTURE FORMATION OF CROSSLINKED POLYSTYRENE

In order to study the mechanism of the formation of maeroporous copolymer, the overall reaction kinetics, phase separation and gelation of the S/EGDM in the presence of inert solvents and the physical properties of the eopolymer were investigated and compared with the corresponding system of S/DVB and S/DVB/MMA. The formation of the network structure of the macroreticular polymer was studied and a model of the mechanism suggested.     

Polymer stabilisers for temperature-induced dispersion gelation: versatility and control

In this study the temperature-induced gelation of butadiene-acrylonitrile latex containing the added temperature-responsive polymer surfactant, poly(NIPAM-co-PEGMa) is investigated for the first time. (NIPAM and PEGMa are N-isopropylacrylamide and poly(ethylene glycol)methacrylate, respectively.) The results are compared with temperature-induced gelation of oil-in-water emulsions containing 1-bromohexadecane. The effect of added anionic surfactant, NaDBS (sodium dodecylbenzene sulfonate) on the temperature-induced gelation process and mechanism is considered. It was found that the gelation temperature (T(gel)) for the latex occurs at the cloud point temperature (T(cpt)) of the polymer and that T(gel) is much less affected by added NaDBS than is the case for emulsion gelation. The mathematical predictive theory recently derived for temperature-induced emulsion gelation was applied to the latex data and gave a good fit (i.e., T(gel) approximately 1/C(p), where C(p) is the concentration of added poly(NIPAM-co-PEGMa)). However, the causes for the variation of T(gel) with C(p) for temperature-induced latex and emulsion gelation are different. The variation of T(gel) for latex gelation in the presence of added NaDBS originates from surfactant association with poly(NIPAM-co-PEGMa) which increased T(cpt). In the case of emulsion gelation there are electrostatic interactions above T(cpt) which control T(gel). The subtle difference in the temperature-induced latex gelation mechanism is a consequence of the very high latex surface area (cf. emulsion), small inter-particle separation and the presence of electrolyte. The reason that T(gel) follows 1/C(p) for the latex is due to a fortuitous T(cpt) approximately 1/C(p) relationship that applies for poly(NIPAM-co-PEGMa) solution in the presence of NaDBS. The work presented here shows that addition of poly(NIPAM-co-PEGMa) to dispersions gives a versatile method for temperature-triggered gelation. Furthermore, the theory presented provides a framework for predicting their gelation temperatures.     

Gelation of "catanionic" vesicles by hydrophobically modified polyelectrolytes

The gelation of mixed cationic/anionic surfactant vesicles of sodium dodecyl sulfate/didodecyldimethylammonium bromide and sodium dodecylbenzenesulfonate/cetyltrimethylammonium tosylate by hydrophobically modified sodium polyacrylate is studied rheologically. When the vesicles are cationically charged, mixtures with this anionic polyelectrolyte form precipitates. When the vesicles are anionically charged, however, these mixtures display a progression from a Maxwell fluid to a critical gel to a solidlike gel with increasing vesicle and/or polyelectrolyte concentration. Consideration of the viscous behavior with increasing vesicle and polymer volume fraction indicates that the gel network is formed by the bridging of the hydrophobically modified polymer between vesicles. The similarity between the gelation results for the two anionic systems suggests the results can be generalized to other similarly charged mixtures.     

Study of the polymer concentration and polymer/crosslinker ratio effect on gelation time of a novel grafted polymer gel for water shutoff using a central composite design method

In this research article, a hydrogel was prepared by crosslinking of carboxymethyl cellulose‐g‐polyacrylamide copolymer aqueous solution with chromium(III) acetate for the purpose of a water shutoff job in the oil reservoir. The experiments were conducted to investigate the main effects of copolymer concentration and crosslinker/copolymer ratio on gelation time of the hydrogel system. Then the effects of these two factors and their interactions on the gelation time were determined by using a central composite design (CCD) of the response surface method. CCD was used to generate the quadratic mathematical model for the gelation time response as a function of copolymer concentration, crosslinker/copolymer ratio, and their interaction. Furthermore, the analysis of variance (ANOVA) was used to evaluate the quality of the quadratic model. The ANOVA result of the developed model showed that the model was highly significant. The result also showed that the crosslinker/polymer ratio had more effects on the gelation time than did the polymer concentration and their interaction. A response surface method provides an optimum gel formulation. Core flooding experiments reveal that a significant permeability reduction on the sand pack cores can be achieved at reservoir conditions, when it is treated with an optimum gel formulation. Hence, this gel system may be suitable in the water shutoff job required for enhanced oil recovery from the oil fields. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of SDS on the gelation of hydroxypropylmethylcellulose hydrogels

Thermal behavior of aqueous hydroxypropylmethylcellulose (HPMC)/surfactant mixtures was studied in the dilute concentration regime using micro-differential scanning calorimetry (DSC). The surfactant used was sodium n-dodecyl sulfate (SDS). The heat capacity of HPMC gel with various concentrations of SDS was much higher than that of the pure HPMC gel. The addition of SDS at different concentrations showed dissimilar influences on the gelation of HPMC; SDS at lower concentrations (≤6 mM) did not affect gelation temperature significantly except for enhancing the heat capacity whilst SDS at higher concentrations (≥6 mM) not only resulted in the gelation of HPMC at higher temperatures but also changed the pattern of the gelation thermograph from a single mode to a bimodal. On the basis of the observed thermal behavior of HPMC/SDS systems, the mechanism behind the sol-gel transition was discussed in terms of the properties of the surfactant and their influences on the extent of polymer/surfactant binding and polymer/polymer hydrophobic association. Gelation kinetics was analysed using the results from the DSC measurements. The kinetic parameters were determined.     

低温聚乙烯醇(PVA)水凝胶结构的初步研究

本文采用透射电子显微镜(TEM)研究了低温PVA水凝胶的结构,直接观察到该体系呈明显的相分离结构,可将所形成结构视为聚集态水平上的宏观网络结构,认为正是这种网络结构的形成而赋予了体系强度和弹性.观察到,随着冷冻时间的增长,逐渐形成完善的网络结构,随着体系中PVA浓度的增大,网络结合得更加紧密.还从DSC测定了该相分离结构解体的热焓变化,进一步证实了显微镜的观察结果,提出了该体系凝胶化过程的宏观机制.     

Influence of Molar Mass and Concentration on the Thermogelation of Methylcelluloses

In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration.     

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。     

Effect of mixed solvent on solution properties and gelation behavior of poly(vinyl alcohol)

In this work, the static and dynamic light scattering measurements were used to investigate the solution properties and the aging effects on PVA/DMSO/water ternary system in dilute region at 25 °C. It was found that the phase separation and aggregate behavior occurs rapidly and obviously when DMSO mole fraction (X₁) in the solvent mixture is between 0.2 and 0.33, especially at 0.25. In this solvent composition range, a broad peak which indicates phase separation and chain aggregation can be observed from static light scattering measurement. However, when DMSO mole fraction is increased to 0.37, no such peak is present. For this ternary system, the gelation mechanism and the relationship between the phase separation behavior and the gelation of the formed physical gels were also investigated through the gelation kinetic analyses in the dilute and semi-dilute region. It is concluded that the cononsolvency effect in the dilute solution is not the sole origin that affects the phase separation, aggregation, and gelation behavior for the ternary system in a higher polymer concentration range. The hydrodynamic factors such as the higher viscosity and slower polymer chain diffusion that are resulted from higher polymer concentration should be also considered.     

Radiation-induced crosslinking of polyvinyltrimethylsilane in the presence of ethylene glycol dimethacrylate and allyl methacrylate

Radiation-induced crosslinking of homogeneous glassy polyvinyltrimethylsilane was carried out either by the γ-irradiation of the polymeric films containing 3–20 wt% of ethylene glycol dimethacrylate or by the radiation-induced grafting of allyl methacrylate from vapour phase onto films made of pure polymer. The dependence of grafting value on the absorbed γ-irradiation dose and film thickness was investigated. The modified films were analyzed for the sol/gel content and the dependence of gel fraction yield of crosslinked polymer on absorbed dose, concentration of the crosslinking agents and film thickness.The radiation-chemical yields of crosslinking and degradation as well as gelation doses were calculated. The permeability of oxygen and nitrogen through the crosslinked films was determined.     

Glassy correlations and microstructures in randomly cross-linked homopolymer blends

We consider a microscopic model of a polymer blend that is prone to phase separation. Permanent cross-links are introduced between randomly chosen pairs of monomers, drawn from the Deam-Edwards distribution. Thereby, not only density but also concentration fluctuations of the melt are quenched-in in the gel state, which emerge upon sufficient cross-linking. We derive a Landau expansion in terms of the order parameters for gelation and phase separation, and analyze it on the mean-field level, including Gaussian fluctuations. The mixed gel is characterized by thermal as well as time-persistent (glassy) concentration fluctuations. Whereas the former are independent of the preparation state, the latter reflect the concentration fluctuations at the instant of cross-linking, provided the mesh size is smaller than the correlation length of phase separation. The mixed gel becomes unstable to microphase separation upon lowering the temperature in the gel phase. Whereas the length scale of microphase separation is given by the mesh size, at least close to the transition, the emergent microstructure depends on the composition and compressibility of the melt. Hexagonal structures, as well as lamellas or random structures with a unique wavelength, can be energetically favorable.