Diffusion in polyacrylamide gels

Using a novel sorption technique, the diffusion of some series of solutes in polyacrylamide gels has been investigated with regard to: (a) molecular size of solute; (b) concentration of solute and gel polymer; and (c) temperature. The approach used also yields the partition coefficient pertaining to sorption equilibrium. The ratio, $\text{D}\text{D}{}_{\mathrm{o}}$, where D_o refers to diffusion in the pure solvent, is found to reflect in part the characteristic interactions between solute and gel polymer. The temperature results indicate that the apparent activation energy for solute diffusion is approximately independent of the polymeric component for dilute gels.     

Collapse of polyacrylamide gels

Summary Ageing of polyacrylamide gels is connected with the formation of charged groups on network chains. The presence of the electrostatic charges is required for the observation of the gel collapse.Presented at the 7th IUPAC Discussion Conference Polymer Networks, Karlovy Vary, CSSR, September 15–19,1980on leave from the Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 162 06 Prague 6, Czechoslovakia     

Formation and structure of polyacrylamide gels

Acrylamide and N,N′-methylenebis (acrylamide) (AAm–Bis) copolymerization has been in-vestigated in water at a monomer concentration of 1.8 w/v%. Conversion of monomer and pendant vinyl groups was measured as a function of the reaction time up to the onset of macrogelation. Experimental results indicate that 80% of pendant vinyl groups are consumed by cyclization reactions. When the monomer concentration was kept constant at 1.8%, the critical conversion at the gel point shows a minimum at 7.5 mol % Bits. The equilibrium degree of swelling of the polyacrylamide (PAAm) gels is independent of their crosslinker content. Calculation results show that the average reactivity of pendant vinyl groups for intermolecular links decreases as the Bis concentration increases. All these results suggest formation of PAAm microgels prior to the onset of macrogelation. As the reaction proceeds, microgels are connected to a macrogel through their peripheral pendant vinyls and radical ends, whereas those in their interior remain intact. The microgels seem to act as the junction points of the final inhomogeneous networks. © 1996 John Wiley & Sons, Inc.     

Friction coefficient in gelatin and polyacrylamide gels

Summary The slow neutron transmission technique is used to measure the friction coefficient f of gel macromolecules moving against a solvent. It is shown that in the range of concentrations C=3–30%, f of gelatin gels is linearly dependent on C. The values of the monomer friction coefficient of gelatin and the friction coefficient at infinite dilution are determined. It is demonstrated that the friction coefficient of polyacrylamide gels varies as the viscosity of a solvent in a wide temperature range, however at temperatures below 25°C the deviation from proportionality is observed.     

Swelling equilibria for heterogeneous polyacrylamide gels

To correlate swelling equilibria for heterogeneous polyacrylamide gels in water to the monomer concentration at preparation, it is necessary to modify the classic Flory–Rehner theory. The necessary modification concerns the relation which links the number of segments between juction points to the monomer concentration at preparation; that relation is here adjusted empirically. Modified theory is compared to experimental swelling equilibria for polyacrylamide gels synthesized in water by free-radical copolymerization of acrylamide (AAm) and N,N′-methylenebis(acrylamide) (BIS) at various monomer concentrations. Synthesis conditions studied are (1) different AAm-to-BIS ratios with fixed total monomer concentrations, (2) different total monomer concentrations with fixed AAm-to-BIS ratios, and (3) different AAm-to-BIS ratios with a fixed number of BIS moleculcs. The modified theory and experiment show good agreement. © 1996 John Wiley & Sons, Inc.     

Heterogeneities in polyacrylamide gels immersed in acetone-water mixtures

Summary Immersion of polyacrylamide gels in acetone-water mixtures with a high content of acetone leads to the formation of heterogeneous structures. The extent of heterogeneity increases as the initial swelling degree of the gel increases, or, as the polarity of the nonsolvent decreases. The nature of the deswelling curves indicates that the polymer-rich regions of the gel formed by the collapse transition block the solvent diffusion outside the gel. This prevents the equilibration of the gel volume with surroundings. Received: 14 April 1998/Revised version: 17 June 1998/Accepted: 17 June 1998     

Effects of inhomogeneities in polyacrylamide gels on thermodynamic and transport properties

The difference in swelling of polyacrylamide gels of various polymer concentrations and the nuclear magnetic resonance self-diffusion measurements of water in these gels suggest that inherent inhomogeneities in dilute gels play an important role in the thermodynamic and transport properties of these gels.     

Newly designed polyacrylamide/dextran gels for electrophoresis protein separation: synthesis and characterization

Newly designed gels for electrophoresis protein separation were synthesized from acrylamide, N,N′‐methylenebis (acrylamide) and dextran mixtures. Radical polymerization was initiated by ammonium persulfate and N,N,N′,N′‐tetramethylethylenediamine. The time dependence of absorbance during polymerization was monitored using UV‐visible spectroscopy. The exothermic polymerization process exhibited a sharp rise of temperature reminiscent of the Trommsdorff effect. The swelling kinetics of the synthesized gels was examined in deionized water and buffer solutions. One of the challenges was to find an alternative to commercial products, sold as mixtures with no detailed chemical contents, commonly used in sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS‐PAGE) for protein separation. For this reason, a systematic comparison was made of the properties of one of the most commonly used commercial gels, Duracryl^? from Genomics Solution Inc., and those of the synthesized polyacrylamide/dextran gels. Copyright © 2011 Society of Chemical Industry     

Synthesis and applications of polyacrylamide gels catalyzed by silver nitrate

Polyacrylamide gels are widely used as matrices for biomolecular analysis and fractionation, and they are being developed as biomaterials for diverse medical and industrial applications. This study reports silver nitrate as a novel catalyst for the synthesis of polyacrylamide gels from acrylamide and N,N‐methylene bisacrylamide monomers. The conditions were defined for silver‐catalyzed, free‐radical‐induced polymerization, and a suitable buffer system was devised for the electrophoretic resolution of nucleic acids. A silver‐staining procedure was modified for these gels, and they were compared with N,N,N′,N′‐tetramethylethylenediamine‐catalyzed gels for sensitivity and gel background. Silver nitrate and ammonium persulfate at final concentrations of 100 and 625 μg/mL, respectively, polymerized the resolving gels within 20 min at room temperature. These gels exhibited antimicrobial properties. The gels with ≥10 μg/mL silver nitrate showed a zone of complete inhibition of Staphylococcus aureus growth on a Luria–Bertani agar plate. The silver‐catalyzed gels were also suitable as antigen‐ and drug‐delivery devices. Silver, acting as both a catalyst and a microbicidal agent, was better than N,N,N′,N′‐tetramethylethylenediamine for the synthesis of polyacrylamide gels as drug‐ and oxygen‐delivery devices for topical applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and relaxation properties of medical‐purposed polyacrylamide gels

By IR and NMR spectroscopy methods, thermomechanical analysis, mechanical relaxation measurements, and computational simulation the effect of production conditions of acrylamide copolymer and N,N′‐methylenebisacrylamide derived hydrogels with respect to their properties were studied. Four hydrogel samples, prepared under different production conditions (γ‐radiation dose and autoclaving), were investigated. It was found that autoclaving and γ‐radiation lead to a slight increase of the crosslinking degree in the polymeric network and formation of alkene structures in polymeric chains. Stress relaxation and creep processes under axial compression of gel cylindrical samples were studied in detail. To approximate stress relaxation and creep curves new memory functions were used, based on the analysis of entropy production in the system during the relaxation process. It was found that primary γ‐radiation of initial gels induces an increase of quasi‐equilibrium rubbery elasticity modulus, and quasi‐equilibrium compliance is decreased. The opposite situation is observed during further autoclaving at 120°C. After autoclaving, required to sterilize the gels, their treatment by γ‐radiation again induced a noticeable increase of the modulus and compliance decrease. The mechanism of relaxation processes was found to be associated with the limiting stage of physical interaction between relaxants, representing different micro‐inhomogeneities in the material. The investigation results were compared with the data obtained by histology and morphology methods. A hydrogel obtained under additional γ‐radiation treatment and autoclaving did not swell when implanted into a living organism, and the tissue reaction to implantation of such gel was minimal. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1043–1058, 2005     

Photon transmission technique for monitoring formation and swelling of polyacrylamide gels

The in situ, real-time photon transmission technique was used to monitor the free radical crosslinking copolymerization of acrylamide and N,N′-methylenebisacrylamide (Bis). Gelation experiments were performed with various Bis contents at various wavelengths. It was observed that the transmitted photon intensity, I _tr, decreased dramatically at a certain reaction time, which is attributed to the increase in scattered light intensity, I _sc, during the formation of microgels in the system. The increase in I _scwas modeled using Rayleigh's equation where the reaction time was found to be proportional to the volume of the microgels. The disc-shaped polyacrylamide (PAAm) gels were dried before use during swelling experiments. Transmitted light intensity, I _tr, from the gel increased at initial stages when PAAm gels were immersed in water and then decreased exponentially as the swelling time increased. Decrease in I _trwas attributed to the lattice heterogeneities, which might have originated between microgels and holes in the swelling gel. Decrease in I _trwas modeled using the Li–Tanaka equation from which cooperative diffusion coefficients, D _c, were determined for gels of various Bis contents. It is observed that the D _cvalues increased with the Bis content.     

Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels

A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5% of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole%, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions. Received: 30 May 1997/Accepted: 26 June 1997     

Heavy metal removal using hydroxypropyl cellulose and polyacrylamide gels,kinetical study

In this article we report the removal of Pb, Ni and Cu using a hydrogel made with hydroxypropyl cellulose (HPC) and polyacrylamide (PAAm). The hydrogel successfully removed those metals, as shown by the results of atomic absorption spectroscopy; the polymer removed 53% of Pb, 52% of Ni and 51% of Cu. Different pHs were tried for these polymers. The highest metal removal was found at 40°C. The adsorption kinetics fitted Langmuir and Freundlich isotherms. Metal particles were detected on the hydrogel with electron microscopy and energy–dispersive X–ray spectroscpy, confirming that the gel removed the metals from the testing solutions. This polymer is a good option for treating wastewater and industrial waters as it removes metals and is composed of nontoxic materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43285.     

Ion‐conducting polymer gels of polyacrylamide embedded with K2CO3

A highly ionic conductive solid‐gel membrane based on polyacrylamide hydrogels with a K₂CO₃ additive was investigated. The polymer‐based gel was prepared by adding ionic species K₂CO₃ to a monomer solution followed by polymerization. After polymerization, the ionic species was embedded in the polymer‐based gel, where it remained. The ionic species behaved like a liquid electrolyte, whereas the polymer‐based solid‐gel membrane provided a smooth impenetrable surface that allowed for the exchange of ions. The gel membranes were obtained in the form of thin films of reasonable mechanical strength. Their ambient temperature conductivities were in the range 10^?2 to 10^?1 S/cm. The effect of K₂CO₃ concentration on the conductivity of the gels prepared was examined in the temperature range from 0 to 100°C. The microstructure and chemical composition of the gels studied were characterized by environmental scanning electron microscopy and FTIR, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2076–2081, 2004     

大豆蛋白/聚丙烯酰胺复合膜的性能研究

制备浓度6%的聚丙烯酰胺与大豆蛋白浆液,研究聚丙烯酰胺含量对浆液的粘度、pH值、粘附力以及浆膜断裂强度、断裂伸长率、耐磨性、吸湿性和水溶性的影响。结果表明,随着聚丙烯酰胺含量的增加,浆液的粘度与粘附力不断增大,pH值降低,浆膜耐磨性变化不大,水溶性有所降低,断裂强度先增大后减小,断裂伸长率则先减小后增大。在聚丙烯酰胺含量40%时,断裂强度为32.374 N,断裂伸长率为23.065%,吸湿率为20.53%,浆膜柔韧性和吸湿性得到显著改善,可以应用于经纱上浆。     

Synthesis and characterization of partially hydrolyzed polyacrylamide nanocomposite weak gels with high molecular weights

High‐molecular‐weight partially hydrolyzed polyacrylamide nanocomposite (HPAMNC) weak gels were synthesized and evaluated for their flooding behaviors in oil‐recovery applications. The structure, morphology, and properties of the obtained HPAMNC samples and their weak gels were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). XRD patterns clearly proved the exfoliation of the montmorillonite (MMT) layers in the polymer matrix; this was consistent with TEM analysis. The morphology of the HPAMNC was proven to be in a cross‐wire aggregated form by SEM analysis. The viscosity‐average molecular mass of the obtained HPAMNC was approximately 8.51 × 10⁶ under the optimized MMT load at 1.0 wt %. The flooding experiments showed that the oil‐recovery rates in sand pack tubes with low and high permeability were enhanced by approximately 35.1 and 46.2%, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42626.     

大豆蛋白/聚丙烯酰胺复合膜的性能研究

制备浓度6%的聚丙烯酰胺与大豆蛋白浆液,研究聚丙烯酰胺含量对浆液的粘度、pH值、粘附力以及浆膜断裂强度、断裂伸长率、耐磨性、吸湿性和水溶性的影响。结果表明,随着聚丙烯酰胺含量的增加,浆液的粘度与粘附力不断增大,pH值降低,浆膜耐磨性变化不大,水溶性有所降低,断裂强度先增大后减小,断裂伸长率则先减小后增大。在聚丙烯酰胺含量40%时,断裂强度为32.374 N,断裂伸长率为23.065%,吸湿率为20.53%,浆膜柔韧性和吸湿性得到显著改善,可以应用于经纱上浆。     

Rheological and thermal stability of novel weak gels based on sulfonated polyacrylamide/scleroglucan/chromium triacetate

The present study deals with weak gels based on sulfonated polyacrylamide (SPA)/scleroglucan (SC)/Cr³⁺ with an exceptional thermal stability in electrolyte media. The rheological results showed that on increasing the SC concentration the shear viscosity and storage modulus of the SPA/SC/Cr³⁺ system were increased and the dependence of the storage modulus on frequency became weaker. The yield stress of the SPA/SC/Cr³⁺ system was higher than that of the corresponding SPA/SC system. The thermochemical stability increased with increasing relaxation time. The SPA/SC/Cr³⁺ semi‐interpenetrating network exhibited the lowest viscosity loss in electrolyte media; therefore this system may be a potential candidate for enhanced oil recovery applications. © 2016 Society of Chemical Industry     

Influence of pore size distribution on water adsorption on silica gels

The influence of pore size distribution on water adsorption has been analysed for a series of partially dehydroxylated silica gels with different pore structure, assessed from the analysis of nitrogen and CO₂ adsorption isotherms. It has been observed that some silica gels show water adsorption mainly in the first range of relative pressures (relative pressure from 0 up to 0.6), while other silica gels also show water adsorption at higher relative pressures. Comparison of the N₂ and water adsorption isotherms points out that only silica gels containing mesoporosity show water adsorption at relative pressures higher than 0.6. Moreover, a good correlation between the initial part of water adsorption isotherms (relative pressure from 0 up to 0.3) and CO₂ adsorption isotherms has been found (the higher the CO₂ adsorption capacity, the higher the water adsorption capacity at low pressure).     

Swelling and dissolution in cleaning of whey protein gels

Fluid dynamic gauging was used to study swelling and dissolution, under alkaline conditions, of heat-induced gels prepared from solutions of β-lactoglobulin (βLg), a whey protein isolate and whey protein concentrate. Recent developments in the understanding of the cleaning behaviour of proteinaceous dairy foulant, obtained using heat-induced βLg gels, are summarised. The thickness-time profiles for βLg gels exhibited Fickian behaviour, whilst the whey protein-based systems showed linear swelling behaviour. The pH values at which the latter gels started to swell were significantly higher than those observed for βLg, while they all showed a pH/volume fraction threshold for dissolution. These differences in swelling and dissolution behaviour are related to the structure of the gels, i.e. fine stranded vs. particulate, and suggest that the key step in the alkaline dissolution of industrial dairy foulants is the conversion of particulate gels to the fine-stranded form.