Preparation and pH‐sensitive swelling behavior of physically crosslinked polyampholyte gels

A novel polyampholyte hydrogels were prepared by free radical aqueous copolymerization of ionic complex consisting of acrylic acid (AAc), (N,N‐diethylamino) ethyl methacrylate (DEAEM), and acrylamide (designated as PADA). Without any chemical crosslinker, the formation of PADA network structures was mainly attributed to the electrostatic interaction of AAc (anionic monomer) and DEAEM (cationic monomer). The PADA gels exhibited a typical swelling behavior of polyampholyte gels in buffer solutions. The hysteresis of isoelectric point (pI) for PADA gels was observed after preswollen in alkaline solutions. The swelling behavior of PADA gels in response to change of pH was investigated. It was found that the equilibrium swelling ratio orderly decreased in buffer solutions with alternating pH between 2.2 and 5. An abrupt swelling was observed for the hydrogels at the pH near isoelectric point in the earlier stage of swelling process. The study of swelling kinetics of the hydrogels showed that the swelling process was in agreement with the second‐order swelling kinetics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3857–3861, 2006     

Contributions of the crosslinked and noncrosslinked moieties to the solvent-induced swelling of brown coals

A suite of brown coals from different sources was examined for solvent-induced swelling in two forms: oven-dried whole coal and pyridine-extraced coal. This enabled the swelling to be resolved into the component due to imbibition of solvent by the crosslinked part and the component due to the non-crosslinked part.     

Mechanical and swelling properties of polyacrylamide gel spheres

Spheres of crosslinked acrylamide-methylene bisacrylamide copolymer were produced by suspension polymerization. By introducing a vibrating stream of aqueous solution into an organic matrix, particle sizes of 0.33 ± 0.06 to 0.99 ± 0.41 mm in diameter resulted. The swelling of gel spheres in water was compared to that of larger ‘bulk’ gels, and a significant amount of hydrolysis occurred in the spheres due to the presence of tetramethylethylenediamine (TEMED), used as an initiator. The dependence of the elastic modulus of the gel spheres upon the crosslinker concentration was non-linear, even in the regime where linearity is observed for bulk gels; this appears to be due to the varying amounts of TEMED that diffuses in the spheres and is known to affect the modulus of bulk gels.     

Cs-AA-HEMA复合水凝胶的合成及溶胀性能

以壳聚糖、丙烯酸、甲基丙烯酸羟乙酯为原料,硝酸铈铵、过氧化二苯甲酰为引发剂,戊二醛为交联剂,制备了壳聚糖-丙烯酸-甲基丙烯酸羟乙酯复合水凝胶,探讨了凝胶溶胀过程和理论,研究了凝胶合成条件及溶剂性质对凝胶平衡溶胀度的影响.结果表明：随着丙烯酸浓度、甲基丙烯酸羟乙酯添加量的增加,凝胶平衡溶胀度先增大再减小,凝胶溶胀度随着戊二醛浓度增加而减小.壳聚糖-丙烯酸-甲基丙烯酸羟乙酯复合水凝胶是pH/离子/温度敏感型凝胶.     

DSC studies on states of water in crosslinked poly(methyl methacrylate-co-n-vinyl-2-pyrrolidone) hydrogels

Mixtures of methyl methacrylate (MMA) with N-vinyl-2-pyrrolidone (VP) of various composition in the presence of fixed concentration of ethylene glycol dimethacrylate (EDMA) have been copolymerized to 100% conversion by γ-irradiation. The resultant solid xerogels were swollen in water to yield hydrogels of equilibrium water contents ranging from 15 to 76wt%. The state of water in the poly(MMA-co-VP) hydrogels has been studied by differential scanning calorimetry (DSC) and the percentages of free freezing, freezable bound and nonfreezing water were found to vary with the xerogel composition, i.e. the degree of hydration of the hydrogels. At low equilibrium swelling, most of the water exists as a non-freezing type, whereas at higher equilibrium swelling the majority of water exists as free freezing water. The maximum number of non-freezing water molecules per VP unit in the hydrogel is about 7.5.     

Synthesis and swelling properties of new crosslinked polyorthocarbonates

Crosslinked polyorthocarbonates were synthesized by the condensation of tetraethyl orthocarbonate and hydroxyl functional monomers. The main goal of this study was to produce a solvent‐absorbent polymer with a high absorption capacity and to use these polymers for the removal of organic solvents from the environment and the recovery of these solvents. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, solid‐state ¹³C‐NMR spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. All of the polymers (except Poly 1 and Poly 2 ) had a high and fast uptake ability for organic solvents, such as tetrahydrofuran, dichloromethane, benzene, and acetone. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The water state in crosslinked poly(vinyl alcohol)–collagen hydrogel and its swelling behavior

Poly vinyl alcohol (PVA) with pendent carboxyl group was synthesized and verified. The collagen was chemical crosslinked with the produced PVA under the help of crosslinker. Then, the PVA–collagen hydrogels were prepared through the repeated freezing–thawing. Since the water states in hydrogels play an important role in the performance of the product, thermogravimetric (TG) analysis and differential scanning calorimeter (DSC) were conducted to study the different states of water. The results indicated that the weight ratio of nonfreezable water to dry gel in PVA–collagen hydrogels was about 25%. Meanwhile, the swelling behaviors in distilled water and 0.9% saline were studied. The one‐phase exponential associate equation can fit the process very well. Calculated from the simulation equation, the swelling ratios at equilibrium in distilled water and saline were 14.353 g/g dry gel and 14.205 g/g dry gel, respectively. The results illustrated that the ions in solution would decrease the swelling ratio of the hydrogel. At the same time, the lyophilization might have slighter influence to the microstructure of hydrogels and should be more suitable for the swelling research than heat drying. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Equilibrium swelling studies of highly swollen acrylamide/mesaconic acid hydrogels

Acrylamide/mesaconic acid (AAm/MA) hydrogels were prepared by free radical solution polymerization in aqueous solution of acrylamide (AAm) with mesaconic acid (MA) as comonomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4‐butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. The influence of mesaconic acid content in hydrogels was examined. Swelling of AAm/MA hydrogels was increased up to 2301% (for containing 20 mg MA and crosslinked by EGDMA) to 3296% (for containing 80 mg MA and crosslinked by BDMA), while AAm hydrogels swelled up to 1330% (crosslinked by BDMA) to 1400% (crosslinked by EGDMA). The values of equilibrium water content of the hydrogels are 0.9301–0.9706. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non‐Fickian in character. Diffusion coefficients of AAm/MA hydrogels were calculated by the short time approximation and found to be from 38.01 × 10^?6 cm² s^?1 to 182.73 × 10^?6 cm² s^?1. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2253–2259, 2005     

依兰煤在液化溶剂中的溶胀动力学研究

笔者以依兰煤为原料,研究了依兰煤在室温至2000℃范围内在液化起始溶剂和循环溶剂中的溶胀行为,并确定了依兰煤在试验条件下的溶胀动力学参数。试验结果表明：依兰煤在液化起始溶剂和循环溶剂中的溶胀度随溶胀温度的增加和溶胀时间的延长而增大;依兰煤在这2种溶剂中的溶胀都是受Case-Ⅰ扩散控制为主的过程,其溶胀活化能分别为4．18和4．22kJ·mol^-1。     

Cationic polyacrylamides increase the rate of liquefaction and hydrolysis of cornstarch

Cationic polyacrylamides (c‐PAMs) bind to starch granules and decrease the temperature for the onset of gelatinization by 8^°C. c‐PAM increases the binding of α‐amylase to cornstarch; the rate of cornstarch hydrolysis also increases. By analogy to previous work on the c‐PAM promoted hydrolysis of cellulose, it is proposed that the polymer reduces the charge on the surface of starch through a charge‐patch mechanism. Because both enzyme and substrate are negatively charged, the bound c‐PAM reduces the charge repulsion experienced by the approaching enzyme, which leads to stronger enzyme‐substrate binding and faster hydrolysis. Overall, the c‐PAM reduces enzyme dose by up to 62% under the conditions used. There is a mirror image relationship between the viscosity of the medium and the hydrolysis rate, which allows optimization of these parameters with enzyme and c‐PAM dosage. Low c‐PAM levels increase viscosity by agglomerating the substrate, but the viscosity drops at higher c‐PAM concentration. © 2012 American Institute of Chemical Engineers AIChE J, 59: 79–83, 2013     

新疆伊犁煤溶胀行为的研究

本文研究了新疆伊犁煤在甲苯、甲醇、四氢呋喃（THF）、N-甲基吡咯烷酮（NMP）和陆梁原油不同溶剂下的溶胀行为,考察了煤预处理温度、不同溶剂、煤／溶剂体积比、溶胀时间对煤溶胀度的影响。结果表明：经过110℃真空干燥预处理煤样的溶胀度大于经过50℃真空干燥预处理煤样的溶胀度;相同条件下,NMP的溶胀度最大;煤／溶剂体积比越大,煤的溶胀度越小;溶胀24h煤样的溶胀度同溶胀60h煤样的溶胀度变化不大。     

果胶-g-聚(丙烯酸-co-丙烯酰胺)水凝胶溶胀性能研究

在水溶液中通过接枝共聚法制备出果胶-g-聚(丙烯酸-co-丙烯酰胺)水凝胶(PECAA),研究了PECAA在蒸馏水中的溶胀动力学,考察了其在不同溶剂中的溶胀行为。结果表明,PECAA在蒸馏水中的溶胀动力学过程可分为3个阶段;以PECAA在蒸馏水中的饱和溶胀度为参照值,其在自来水中的饱和溶胀度比值最高,其次为NaCl溶液,在CuSO4溶液中的饱和溶胀度比值最低。     

Effect of polymer solution concentration on the swelling and mechanical properties of glycol chitosan superporous hydrogels

This study examined the effect of the polymer solution concentration on the swelling and mechanical properties of glycol chitosan (GCS) superporous hydrogels (SPHs). GCS SPHs were synthesized using a gas blowing method using glyoxal as the crosslinking agent at different polymer solution concentrations. A small change in the GCS solution concentration resulted in a remarkable change in compression strength and swelling kinetics without any significant loss in equilibrium water imbibing capacity. The increase in mechanical strength accompanied by the decrease in swelling kinetics was caused by the generation of smaller pores during the gelation process of the reactant systems associated with a higher polymer solution viscosity. The apparent diffusion coefficients for a variety of GCS/simulated gastric fluid solution systems were determined from the theoretical fitting of experimental dynamic swelling data, explaining the effects of the solution concentration and crosslinking density on the swelling kinetics. The diffusion coefficients determined in this study are expected to be used as the basic information in estimating the swelling kinetics of samples in different dimension. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of temperature on swelling and mechanical properties of a sulphobetaine hydrogel

The swelling and mechanical properties of a hydrogel based on the zwitterionic monomer N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulphopropyl)ammonium betaine crosslinked with ethylene glycol dimethacrylate have been determined as a function of temperature. The volumetric swelling has been found to decrease slightly with temperature. On the other hand, the Young's modulus as well as the experimental crosslink density increase with temperature. The results obtained have been explained by examining the changes with temperature of the partial molar Gibbs free energy of dilution in conjunction with the variation of its enthalpic and entropic contributions.     

戊二醛对壳聚糖-聚醚水凝胶溶胀动力学的影响

以壳聚糖和聚醚为原料、戊二醛为交联剂合成了壳聚糖-聚醚水凝胶。研究了壳聚糖-聚醚水凝胶溶胀机理,探讨了戊二醛浓度对该水凝胶的溶胀度、溶胀速率和溶胀动力学的影响。结果表明,戊二醛浓度不仅是影响水凝胶溶胀度的主要因素,随着戊二醛浓度的增大,壳聚糖-聚醚水凝胶的溶胀度逐渐减小,而且影响其溶胀动力学类型,当戊二醛浓度为0.107 mol·L^-1,该水凝胶的溶胀过程属于Fickian类型,当戊二醛浓度为0.320、0.533 mol·L^-1,其溶胀过程属于non-Fickian类型。     

Plugging properties and profile control effects of crosslinked polyacrylamide microspheres

In this article, the morphology, particle size, and plugging properties of crosslinked polyacrylamide (CPAM) microspheres were investigated through optical microscopy, scanning electron microscopy (SEM), nuclear‐pore membrane filtration experiments, a micro‐visual model, sandpack experiments, parallel twin‐tube plugging, and oil displacement experiments. The results revealed that the primary particle sizes of the CPAM microspheres ranged from several hundreds of nanometers to 5 μm; however, after the microspheres were fully swelled in water, their sizes increased by approximately five times of their original sizes. As a CPAM microsphere dispersion system had good dispersibility and deformation capabilities, a 1.2 μm nuclear‐pore membrane as well as the deep part of a sandpack tube could be effectively plugged. Consequently, the flow diversion effect was achieved in the vertical and planar directions. When the CPAM microspheres migrated in porous media, they could displace residual oil on the pole wall and water flow channel to realize the synchronization of profile control and coordination and improve recovery efficiency. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43666.     

Aspects of crosslinking sulfonated polyacrylamides from rheological studies on their gels

Crosslinking of sulfonated polyacrylamide by zirconium requires some acrylate sites on polymer chain, and a schematic reaction is proposed to describe this process. Moreover, gelation kinetics is found to be fairly proportional to polymer acrylate site content. On the other hand, decreasing sulfonation level or solvent salt concentration is shown to result in increasing the system gelation, and an explanation of such behavior is attempted. Furthermore, we find that gelation kinetic is highly dependent on zirconium concentration in an unusual manner. So, for a given polymer sample, a maximum of zirconium concentration exists above which gelation kinetic decreases until it vanishes. This behavior is interpreted by existence of a background reaction where highly stable zirconium complexes are formed. This reaction indeed competes against the polymer cross-linking process and zirconium concentration increases. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1067–1072, 1997     

丙烯酰胺类共聚物水凝胶的合成及性能研究

用自由基聚合法合成了不同摩尔配比的HEMA／AM共聚物水凝胶材料。研究了单体组成、温度、pH值、离子强度等因素对凝胶溶胀性能的影响。结果表明：水凝胶的溶胀速度较快;水凝胶在pH值小于4及pH值大于9的酸、碱溶液中发生水解,导致水凝胶的饱和含水量大幅增加,而在弱酸性溶液中几乎没有变化;水凝胶的饱和含水量对离子强度的变化不够敏感;随着温度的升高水凝胶的饱和含水量略有减少,说明此类水凝胶对温度的敏感性也较弱。     

The effects of the pH value of the swelling medium on the kinetics of the swelling of a poly(acrylic acid) hydrogel

The isothermal kinetics curves of the swelling of a poly(acrylic acid) hydrogel in buffer solutions of different pH values (5, 7, and 9) at temperatures ranging from 30 to 40°C were determined. The possibilities of applying the Fick kinetics model and the Peppas equation were examined. It was found that the applicability of these models were limited. The kinetics model of a first‐order chemical reaction was found to describe the swelling kinetics of the PAA hydrogel in all the investigated buffer solution at all the investigated temperatures. Swelling kinetics is determined by the rate of expansion of the network. The kinetic parameters (E_a, ln A) of the swelling of the PAA hydrogel in buffer solutions of different pH values were determined. The activation energy and the pre‐exponential factor of the swelling of the PAA hydrogel in buffer medium decreased with increasing pH value of the swelling medium. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Determination of hydrogel swelling factors by two established and a novel non-contact continuous method

Hydrogels were introduced as suitable materials for applications in, e.g., medical, agriculture, or daily life areas. Swelling characteristics of a hydrogel are important and must be precisely known for various fields of application. In medicine, where hydrogels are used as implants or drug delivery systems, precise knowledge of the swelling behavior is essential. Especially in ophthalmology as part of cataract surgery, the visco-elastic properties of the hydrogels could even allow for the restoration of accommodation. The easiest way to describe the swelling is by measuring the swelling ratio, generally done by scaling. Besides that, it can also be done by volume investigations. The similarities and differences are studied on five hydrogel samples made of methyl methacrylate and N-vinyl pyrrolidone. Additionally, a first camera-based approach, potentially providing an automated, quasi-continuous non-contact method for swelling kinetics investigations, is described.