流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

流变学法研究部分水解聚丙烯酰胺/Cr(Ⅲ)交联反应Ⅰ.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺(HPAM)/Cr(Ⅲ)交联体系的反应动力学.HPAM溶液的粘性模量G"大于弹性模量G＇,且其数值随时间不发生变化,体系为粘性溶液.而HPAM/Cr(Ⅲ)体系的G＇和G"的数值都随时间变化,G"在反应开始阶段大于G＇,当反应进行一段时间后,G＇超过G"占据主要地位,体系成为弹性体系.交联过程可分为三个阶段:第一上升阶段,平缓上升阶段和第二上升阶段.利用G＇～t曲线可以推测反应机理.实验发现成胶速率随反应物HPAM和Cr(Ⅲ)的浓度的增加而增加,而成胶时间缩短.在羧基浓度过量的情况下,交联反应对Cr(Ⅲ)浓度的反应级数是1.凝胶的有效弹性交联密度随聚合物浓度的增加而增加,且随凝胶反应的进行而增加.凝胶的交联点间的链平均分子量随Cr(Ⅲ)浓度的增加和交联反应的进行而下降.     

部分水解聚丙烯酰胺柠檬酸铝体系临界交联浓度的研究

采用落球粘度计、核孔膜过滤、动态光散射 (DLS)和2 7Al NMR法 ,研究了高分子量、低浓度的部分水解聚丙烯酰胺 (HPAM)与柠檬酸铝 (AlCit)体系形成交联聚合物溶液 (LPS)的临界交联浓度 .研究结果表明 ,HPAM AlCit体系在聚合物浓度较低时 ,溶液中主要发生形成交联聚合物线团 (LPC)的交联反应 ,此时形成的是LPS ,聚合物浓度增加到某一临界值后 ,体系中形成线团后 ,存在线团间的交联 ,此时形成的是弱凝胶 .不同方法所测得的HPAM AlCit体系的临界交联浓度基本相同 ,对于粘均相对分子质量为 1 4× 10 7的HPAM ,在NaCl浓度为 2 0 0 0mg L ,交联比 2 0∶1时形成的交联体系 ,其临界交联浓度在 2 0 0～ 30 0mg L间 .     

水解聚丙烯酰胺柠檬酸铝体系成胶行为与形态结构的研究

采用光学显微镜、扫描电镜及流变性能测试等手段 ,研究了部分水解聚丙烯酰胺 (HPAM )与柠檬酸铝 (AlCA)的成胶行为与形态结构 .结果表明 ,当AlCA浓度超过 10 0mg/L时 ,随HPAM浓度由低向高变化 ,HPAM AlCA交联体系可形成三种不同形态结构的凝胶 :分散凝胶 (由交联聚合物颗粒形成的分散体 )、两相(分散凝胶相与连续网状凝胶相 )共存凝胶和连续网状凝胶 .HPAM AlCA形成分散凝胶时 ,无明显的粘度升高现象 ,但体系中存在由HPAM大分子交联在一起的颗粒结构 .HPAM AlCA在形成连续网状凝胶时 ,体系复模量和复粘度大幅度提高 ,网状凝胶中含有粒状凝胶颗粒 .     

原子吸收法研究部分水解聚丙烯酰胺/Cr(Ⅲ)凝胶的交联密度

由 Cr( )交联部分水解聚丙烯酰胺 ( HPAM)形成的水凝胶已广泛应用于油田三次采油生产中 ,对于调整吸水剖面和提高原油采收率起到重要作用 .在 HPAM/Cr( )交联机理和交联动力学等方面的研究多采用粘度法 [1] 、紫外 -可见分光光度法 [2 ] 、流变学法[3] 、原子力显微镜 ( AFM)法 [4 ] 、粒度及其分布法 [5] 等 ,考察 HPAM/Cr( )交联反应过程 ,而对交联密度ρ的研究却少见报道 .ρ可用单位体积凝胶中参与交联反应的 Cr( )的量 ( g/cm3)来表征 ,在微观上反映了交联点的数目 ,在宏观上与凝胶的强度和脱水程度相联系 ,因而是交联体系…     

低浓度部分水解聚丙烯酰胺/柠檬酸铝交联体系剪切稳定性研究

采用粘度法、核孔膜过滤和动态光散射(DLS)法,研究了高分子量低浓度的部分水解聚丙烯酰胺(HPAM)与柠檬酸铝(AlCit)反应所形成的交联体系的剪切稳定性和HPAM剪切降解后与AlCit反应所形成的体系的封堵性能及降解机理.研究结果表明,低浓度的HPAM与AlCit反应所形成的交联聚合物体系随剪切速率增加,其对1.2μm的核孔膜的封堵能力降低.HPAM稀溶液剪切降解后再与AlCit反应,低剪切速率对其封堵性能影响较小,而高剪切速率会使得其封堵性能大大降低.HPAM/AlCit交联体系和HPAM剪切降解后形成的交联体系的封堵性能下降的原因是HPAM/AlCit交联体系中交联聚合物线团(LPC)尺寸和HPAM中高分子线团的尺寸变小.     

柠檬酸铝/聚丙烯酰胺胶态分散凝胶反应动力学和机理的研究

采用粘度法研究了柠檬酸铝（AlCit)与部分水解取丙烯酰胺（HPAM）胶态分散凝胶体系的反应动力学。结果表明，胶态分散凝胶体系的交联反应是一级反应。并推导出胶态分散凝胶体系的反应动力学方程。     

低浓度HPAM/AlCit交联体系的27Al NMR研究

用27Al NMR谱研究了高分子量低浓度的部分水解聚丙烯酰胺(HPAM)与柠檬酸铝(AlCit)体系交联反应过程中Al的化学位移和Al的自旋-晶格弛豫时间的变化. 结果表明, HPAM与AlCit反应后, 与HPAM分子链上的羧基发生配位交联的Al的化学位移向低场移动, 而不参与交联反应的AlCit分子结构中Al的化学位移基本不变. HPAM/AlCit交联体系中存在三种形态的Al, 分别对应三种不同的自旋-晶格弛豫时间. 当HPAM的质量浓度≤200 mg/L时, HPAM与AlCit反应过程中交联态Al的自旋-晶格弛豫时间τ13随反应进行变小, HPAM与AlCit主要发生分子内交联反应. 当HPAM的质量浓度≥250 mg/L时, HPAM与AlCit反应过程中交联态Al的自旋-晶格弛豫时间τ13随反应进行变大, HPAM与AlCit主要发生分子间交联反应.     

粘度法研究胶态分散凝胶交联过程

通过粘度测定方法,研究了部分水解聚丙烯酰胺（ＨＰＡＭ）／ 柠檬酸铝（ＡｌＣｉｔ） 交联过程中粘度变化的特性．聚合物浓度高的ＨＰＡＭ／ＡｌＣｉｔ 体系粘度随反应时间的延长而上升,其体系粘度最终高于相同聚合物浓度的ＨＰＡＭ 溶液粘度．聚合物浓度低的ＨＰＡＭ／ＡｌＣｉｔ 体系粘度随反应时间的延长而下降,其体系粘度低于相同聚合物浓度的ＨＰＡＭ 溶液粘度．ＨＰＡＭ／ＡｌＣｉｔ 交联体系的聚合物浓度低于临界浓度时,交联反应后形成稀胶态分散凝胶（ＴＣＤＧ） ．在实验条件下,临界浓度在１５０ ～３００ｍｇ／Ｌ 之间．当聚合物浓度于临界浓度和７００ｍｇ／Ｌ之间时,形成浓胶态分散凝胶（ＣＣＤＧ） ;当聚合物浓度高于７００ｍｇ／Ｌ 时,ＨＰＡＭ／ＡｌＣｉｔ 交联体系形成整体凝胶．     

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.     

Rheological and swelling behavior of semi‐interpenetrating networks of polyacrylamide and scleroglucan

Preparation and characterization of novel semi‐interpenetrating polymer network (semi‐IPN) hydrogels based on partially hydrolyzed polyacrylamide (HPAM) and scleroglucan solution crosslinked with chromium triacetate are described. Effects of scleroglucan concentration on the gelation process and swelling behavior of synthesized hydrogels in different media were investigated using dynamic rheometery and swelling tests, respectively. Oscillatory shear rheology showed that the limiting storage modulus of the semi‐IPN gels increased with increase in scleroglucan concentration. It was also found that the viscous energy dissipating properties of the semi‐IPN gels decreased with increase in the crosslinker concentration of the gelation system. In addition, the loss factor slightly decreased by increasing the scleroglucan content, indicating that the viscous properties of this gelling system decreased more than its elastic properties. The swelling tests showed that the equilibrium swelling ratio (ESR) of the semi‐IPN networks decreased with increase in scleroglucan content, due to the decrease of ionic groups of polyelectrolyte hydrogel. However, the semi‐IPN gels showed lower salt sensitivity in synthetic oil reservoir water as compared with HPAM gels. Therefore, these semi‐IPN hydrogels may be considered potentially good candidates for enhanced oil recovery (EOR) applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal gelation of cellulose in a NaOH/thiourea aqueous solution

Utilizing a novel solvent of cellulose, 6 wt % NaOH/5 wt % thiourea aqueous solution, for the first time, we prepared the thermally induced cellulose gel. We investigated the thermal gelation of cellulose solutions with rheometry and the structure of the gel with 13C NMR, wide-angle X-ray diffraction, environmental scanning electron microscopy, and atomic force microscopy. The cellulose solutions revealed an increase in both the storage modulus (G') and the loss modulus (G") with an increase in the temperature during gelation. The temperature at the turning point, where G' overrides G" because of the onset of gelation, decreased from 38.6 to 20.1 degrees C with an increase of cellulose concentration from 4 to 6 wt %. Given enough time, G' of all solutions can exceed G" at a certain temperature slightly lower than the gelation temperature, indicating that the occurrence of the gelation is also a function of time. Each of the assigned peaks of NMR of the cellulose gel is similar to that of the cellulose solution, suggesting that the gelation resulted from a physical cross-linking. The gels were composed of relatively stable network units with an average diameter of about 47 nm. At either a higher temperature (at 60 degrees C for 30 s) or a longer gelation time (at 30 degrees C for 157 s), the gel in the 5 wt % cellulose solution could form. A schematic gelation process was proposed to illustrate the sol-gel transition: the random self-association of the cellulose chains having the exposed hydroxyl in the aqueous solution promotes the physical cross-linking networks.     

Effect of Cationic Surfactant on the Gelation of HPAM by Cr(III)

Aqueous gels formed by the crosslinkage of Cr(III) with partially hydrolyzed polyacrylamide (HPAM), have been commonly applied in the field of petroleum production1. Polymer and surfactants are used in enhancement of oil recovery2. Some studies3 indicate that a strong interaction is existent between polyeletrolytes and oppositely charged surfactants. So it is very important to study the effect of cationic surfactants on the gelation process of crosslinkage of Cr(III) with HPAM. To o…     

Rheological study of the sol-gel transition in silica alkoxides

The sol-gel transition of the system tetramethylorthosilicate-water-methanol under basic conditions has been studied by rheological measurements. The gelation time t(g) has been determined from the measurements of the elastic G' and viscous G' moduli as a function of time at different frequencies according to Winter's criterion. At gelation time the frequency dependence of both moduli follows a power law with an exponent related to the fractal dimension of the network structure. Different initial monomer concentrations, hydrolysis molar ratios, and temperatures are studied. The decrease of the gelation time with an increase of initial monomer concentration or hydrolysis molar ratio is well-described by a power law. An apparent activation energy is deduced from the temperature dependence of gelation time.     

Linear Viscoelastic Behavior of Multiphase Dispersions

The linear viscoelastic behavior of polymer-thickened oil-in-water emulsions, polymer-thickened solids-in-liquid suspensions, and their blends is investigated using a controlled-stress rheometer. The emulsions exhibit a predominantly viscous behaviour at low values of oil concentration in that the loss modulus (G") exceeds the storage modulus (G') over most of the frequency range. At high values of oil concentration, the emulsions exhibit a predominantly elastic behavior. The ratio of storage modulus to loss modulus (G'/G") increases with the increase in oil concentration. Emulsions follow the theoretical model of J. F. Palierne (1990, Rheol. Acta 29, 204) only at low values of oil volume fraction (/=G' over most of the frequency range. The ratio G'/G" varies only slightly with the increase in solids volume fraction. The Palierne model describes the linear viscoelastic properties of suspensions accurately only at low values of solids volume fraction. At high values of solids concentration, the Parlierne model underpredicts the linear viscoelastic properties of suspensions and the deviation increases with the increase in solids concentration. The blends of emulsions and suspensions exhibit strong synergistic effects at low to moderate values of frequencies; the plots of blend modulus versus emulsion content exhibit a minimum. However, at high values of frequency, the blend modulus generally falls between the moduli of pure suspension and pure emulsion. The high-frequency modulus data of blends of emulsions and suspensions are successfully correlated in terms of the modulus ratio versus volume fraction of solids, where modulus ratio is defined as the ratio of blend modulus to pure emulsion modulus at the same frequency. Copyright 2000 Academic Press.     

Self‐Assembly Fractal Microstructures of HPAM/Chromium Acetate and HPAM/Phenolic Aldehyde Colloidal Dispersion Gel

Abstract

HPAM (partially hydrolyzed polyacrylamide)/chromium acetate and HPAM/phenolic aldehyde colloidal dispersion gels (CDGs) were investigated microscopically using atomic force microscope. The results show that the colloidal dispersion gels eventually form self‐assembly branch‐like fractal structures over a scanning range of micrometers. The fractal aggregates of single twigs formed by compact assembly of nanometer particles were observed over a smaller scanning range regardless of the concentration of HPAM and the crosslinking reagent. This indicated an HPAM‐dependence for the formation of the fractal structure and the crosslinking reagent independence of the geometrical morphology of the gel. Also, the results demonstrated that the elastic modulus (G′) of the fractal structure formed by the smaller (nanometer‐sized) colloidal particles was one order of magnitude higher than obtained for the micrometer‐sized particles. The elastic modulus (G′) and the dynamic stability of the gels increased with decreasing particle diameter.     

Effect of deacetylation rate on gelation kinetics of konjac glucomannan

Effect of deacetylation rate on the gelation behaviors on addition of sodium carbonate for native and acetylated konjac glucomannan (KGM) samples with a degree of acetylation (DA) range of 1.38-10.1 wt.% synthesized using acetic anhydride in the presence of pyridine as catalyst was studied by dynamic viscoelastic measurements. At a fixed alkaline concentration (C(Na)), both the critical gelation times (t(cr)) and the plateau values of storage moduli (G'(sat)) of the KGM gels increased with increasing DA. While at a fixed ratio of alkaline concentrations to values of DA (C(Na)/DA), the similar t(cr) and (G'(sat)) values independent of DA were observed. On the whole, increasing KGM concentration or temperature shortened the gelation time and enhanced the elastic modulus for KGM gel. The effect of deacetylation rate related to the C(Na)/DA on the gelation kinetics of the KGM samples were discussed.     

低浓度HPAM/AlCit交联聚合物溶液性质研究

采用粘度法、扫描电镜（SEM）、核孔膜过滤、动态光散射（DLS）和27Al NMR法，研究了高分子量低浓度的部分水解聚丙烯酰胺（HPAM）与柠檬酸铝（AlCit）体系交联反应过程溶液性质变化.结果表明，HPAM与AlCit反应在低剪切速率时体系粘度随反应进行而降低，在剪切速率较高时具有剪切稠化现象，HPAM与AlCit反应过程中交联态Al的自旋 晶格弛豫时间随反应进行变短.低浓度的HPAM与AlCit发生分子内交联反应形成交联聚合物线团（LPC）在水中的分散体系，即交联聚合物溶液（LPS）.交联聚合物溶液中LPC的平均流体力学半径约为238 nm，其形态接近球形，具有多分散性. LPS对1.2 μm核孔膜的封堵程度与其反应时间有关.