The gelation of hydroxypropyl guar gum by nano‐ZrO2

In the study, hydroxypropyl guar gum (HPG) gel is prepared by using Nano‐ZrO₂ particles as the cross‐linking agent. The Nan‐ZrO₂ particles are prepared by using oil‐water interface method. The physical properties such as morphology, particle size, and crystal structure of the Nano‐ZrO₂ particles are analyzed by SEM, particle size analyzer, FT‐IR, and XRD, respectively. The results show that the Nano‐ZrO₂ particles are spherical particles with a little agglomeration; these spherical particles have a tetragonal structure and higher crystallinity, and the mean diameter of the first‐level grain is 24 nm. The rheological properties including shear stress, complex modulus, elasticity modulus (G′), and viscosity modulus (G′′) of the Nano‐ZrO₂ cross‐linked HPG gel are investigated. The results show that the Nano‐ZrO₂ cross‐linked HPG gel is a pseudo‐plastic non‐Newtonian fluid with higher elastic modulus (G′ > G′′) and lower tanδ (tanδ < 1, the ratio of viscous and elastic modulus), which indicate that the Nano‐ZrO₂ cross‐linked HPG gel may have potential application in fracturing.     

In situ organically cross‐linked polymer gel for high‐temperature reservoir conformance control: A review

Polymer gel has been established as water‐blocking agents in oil recovery application. In this practice, a mixture known as gelant is injected into target area and set into a semisolid gel after a certain adequate time. Besides profile modification and water shutoff, the role of the polymer gel in conformance control is to block high permeability regions, before diverting injected water from high permeability to low permeability zones of the reservoir. It is to boost the oil displacement and sweep efficiency. This is the key to improve oil recovery in the heterogeneous oil reservoirs. However, very limited gels are applicable for harsh conditions, especially in high‐temperature reservoirs. Organically cross‐linked polymer is 1 of the materials for conformance control at high‐temperature reservoirs. Many experimental works and field applications have exhibited the potential of this technology. This paper presents a concise review on this polymer gel for conformance control at high‐temperature wells. Firstly, in situ organically cross‐linked polymer gel has been introduced, and the reason of the use over other types of polymer gels is summarized. The early studies of organically cross‐linked gel systems are also discussed, followed by the chemistry and the gelation mechanisms. An extensive review on factors that affect gelation kinetics and field applications is also discussed in some detail.     

Rheological behavior and particle suspension capability of guar gum: sodium tetraborate decahydrate gels containing cellulose nanofibrils

Guar gum (GG) fracturing fluids were studied by incorporating cellulose nanofibrils (CNFs) in anhydrous borax crosslinked guar gum gels. To fully understand the impact of CNF on the proppant suspension capability of developed fracturing fluids, their shear rate-dependent viscosity and viscoelasticity were investigated. The shear rate dependencies of fluids was fitted to the Carreau model. The zero shear rate viscosity and elasticity of fracturing fluids increased significantly by incorporating CNF in guar gum gels. On the other hand, the viscosity at high shear rates (>100 s^?1) decreased as desired. The proppant settling velocities through fracturing fluids were evaluated by modeling the terminal falling velocity of proppants moving through a Carreau model fluid. The experimental results of the rheological behavior and the modeling results of the proppant settling rate indicated that the fracturing fluids containing CNF had better suspension capabilities. In addition, the lower viscosities of CNF formulated GG gels at higher shear rates will make them more pumpable.     

Hydrophobic guar gum derivatives prepared by controlled grafting processes

Introduction of polyalkoxyalkyleneamide grafts to guar gum produces a new water soluble guar derivative. Modification of either guar gum or hydroxyopropyl guar is achieved in a three‐step process: carboxymethylation with sodium chloroacetate, esterification with dimethyl sulfate (DMS) and amidation with a series of polyalkoxyalkyleneamines. The process was followed using infrared spectroscopy; the grafted guar derivatives were characterized using ¹H NMR. A series of hydroxypropyl guar (HPR) derivatives with degrees of carboxymethylations ranging from 0.2–0.3 were modified with polyalkoxyalkyleneamines with molecular weights ranging from 300 to 3000. The ratio of oxypropylene to oxoethylene units in the polyalkoxyalkyleneamines was varied from 9/1 to 8/58 to adjust the hydrophobicity of the grafts. Aqueous solutions of the graft copolymers exhibit viscosities one to two orders of magnitude lower than the corresponding solutions of the parent guar gum. Copyright © 2007 John Wiley & Sons, Ltd.     

Behavior of a Metastable Gel of Sodium N‐Stearoyl‐l‐Glutamate/Water System

Gel formation was observed at 25°C in a mono sodium N‐stearoylglutamate (C18GS)/water system by quick cooling (quenching, 15°C/minute), whereas coagel was formed by slow cooling (annealing, 1°C/minute). Two kinds of phase transition temperatures, T_gel (coagel‐gel) and T_c (gel‐liquid crystal or micelle), were detected in the annealing system using a differential scanning calorimeter (DSC). On the other hand, only T_c was observed in the quenching system. Since the phase transition entropies at T_c in both the quenching and annealing systems are similar, both gels are considered to be in the same structure, and the gel observed in the quenching system at low temperature is in the metastable, supercooled state. Judging from the ¹H‐NMR data and microscopic observation, a homogenous gel is formed above 7 wt% of C18GS. With an increase in surfactant concentration, the thixotropic tendency of the gel increases due to the decrease in free‐water. Since it was difficult to show gel formation with the shorter chain homologs, C14GS and C12GS, the hydrocarbon chain length of the surfactant appears to be very important in the formation of a metastable, supercooled gel.     

Hydrophobicity of fluoro‐containing physical crosslinkage domains in hydrophobically modified poly(acrylic acid) gels

A series of hydrophobically modified poly(acrylic acid) gels were prepared by the radical copolymerization of acrylic acid and small amounts of hydrophobic comonomers, 2‐(N‐ethylperfluorooctane‐sulfoamido)ethyl methacrylate and lauryl acrylate, in tert‐butanol. The effects of the fractions and species of hydrophobes on hydrophobic association were determined. The hydrophobic association within the hydrophobically modified gels was proven with measurements of swelling and fluorescence as well as Fourier transform infrared spectroscopy. Fluorocarbon‐modified hydrogels showed stronger hydrophobicity than hydrocarbon‐modified hydrogels. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1236–1244, 2002     

Effects of added surfactants on thermoreversible gelation of associating polymer solutions

The influence of added surfactants on physical properties of associating polymer solutions was examined by a new statistical‐mechanical theory of associating polymer solutions with multiple junctions and by computer simulation. The sol–gel transition line, the spinodal line, and the number of elastically effective chains in the mixed networks were calculated as functions of the concentration of added surfactants. All of them exhibited nonmonotonic behavior as a result of the following two competing mechanisms. One was the formation of new mixed micelles by binding surfactants onto the polymer associative groups. These micelles serve as crosslink junctions and promote gelation. The other was the replacement of polymer associative groups in the already formed network junctions by added surfactants. Such replacement lowers connectivity of junctions and destroys networks. The critical micelle concentration was also calculated. The results are compared with the reported experimental data on poly(ethylene oxide)‐based associating polymers and hydrophobically modified cellulose derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 733–751, 2004     

Effects of microcrystallites on swelling behavior in chemically crosslinked poly(vinyl alcohol) gels

We report the swelling ratio and network structure of a poly(vinyl alcohol) (PVA) gel chemically crosslinked by glutaraldehyde with different degrees of crosslinks. Microcrystallites were formed in a chemical PVA gel during a drying process and were confirmed by X‐Ray diffraction (XRD) measurements and Fourier transform infrared (FTIR) spectroscopy. The formation of microcrystallites in the dried gels was suppressed by increasing the degrees of chemical crosslinks. When the dried samples were immersed in pure water at 25 °C, the swelling ratio depended on the degree of chemical crosslinks resulting from the destruction of physical crosslinks by microcrystallites. On the other hand, when the dried samples were immersed in a poor solvent of a mixture of dimethyl sulfoxide and water at 8 °C, the gels did not swell and stayed in the collapsed state. Starting from the collapsed state, the equilibrium swelling ratios were measured while the temperature was increased to 90 °C and then decreased to 8 °C. As a result, irreversible swelling behaviors were observed for all gels with different degrees of crosslinks, which were attributed to the destruction of microcrystallites. The swelling behavior is discussed in terms of the formation and destruction of additional physical crosslinks in the chemical PVA gels. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Drying dissipative structures of the thermosensitive gels of poly(N-isopropyl acrylamide) on a cover glass

Drying dissipative structural patterns of the thermosensitive gels of poly(N-isopropyl acrylamide) were studied on a cover glass. As the temperature of suspension and room rose from 25 to 50 °C, the small size of drying pattern area extended to the beautiful flickering spoke-like ones transitionally at the critical temperature ca. 35 °C. The principal patterns at 25 °C were the single or multiple broad rings of the hill accumulated with the gels. At 50 °C, on the other hand, the flickering spoke-like patterns were observed at the inner area of the broad ring especially at the gel concentrations higher than 1 × 10⁻³ g/ml. These observations support that the extended gels at low temperatures apt to associate weakly to each other, whereas the gels at high temperatures shrink and move rather freely with the convectional flow of water, though the very weak intergel attractions still remain. In the presence of sodium chloride at high temperatures, the cooperative patterns formed between the gel spheres and the salt. The gravitational and Marangoni convectional flow of the gels and the very weak interactions between the gels and substrate (cover glass) are important for the flickering spoke-like pattern formation.     

Preparation and properties of chitosan‐poly(N‐isopropylacrylamide) semi‐IPN hydrogels

Chitosan (CS), CS‐poly(N‐isopropylacrylamide)(PNIPAM) and their dyed (pyrene) hydrogels were prepared using glutaraldehyde (Glu) as a crosslinker. The gelation rate, swelling behaviors in ethanol/water mixtures, electricity‐induced contraction and thermoresponse of the gels were investigated using fluorescence probe technique. Results showed that CS/Glu, and PNIPAM‐containing CS/Glu gels exhibited similar properties in all aspects examined, except that the transparence of the CS‐PNIPAM/Glu gel is very dependent upon the temperature. The CS‐PNIPAM/Glu gel is transparent below 30°C, whereas opaque above 32°C. It is expected that this observation may be useful for the design and preparation of new kinds of hydrogel devices. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 474–481, 2000     

Tailoring Mesopores in Monolithic Macroporous Silica for HPLC

Mesopore formation in silica gels having continuous macropores has been investigated. The macroporous wet silica gel prepared by the sol‐gel process including phase separation was aged in a basic solvent making use of hydrolysis of urea in a closed condition. The mesopore structure was finally obtained by subsequent evaporation drying of solvent and heat‐treatment at 600°C for 2 h. The dissolution‐reprecipitation kinetics at the interfaces between wet gel skeletons and an external solvent affected the size and volume of pores formed within the skeletons. Below 120°C, mesopores suitable for various chromatographic applications have been formed typically within 24 h. On the other hand, at 200°C, the pore size attained the macropore dimensions (>50 nm), and the whole macroporous morphology was significantly modified.     

An anhydrous sol–gel system derived from methyldichlorosilane

Pyridine‐catalyzed reactions of methyldichlorosilane with bis(trimethylsilyl)carbodiimide afford a dichlorosilane‐derived anhydrous sol–­gel material. Both trimethylchlorosilane formation and Si–H disproportionation act as crosslinking mechanisms. The dried gels form amorphous or crystalline materials, depending on the sample history. The xerogels gave Si/C/N ceramics when pyrolyzed at 1200 °C. Copyright © 1999 John Wiley & Sons, Ltd.     

Gel–sol transition for soluble polyimide solution

Copolyimides were synthesized in N‐methyl‐2‐pyrrolidone (NMP) to prepare polyimide (PI) solutions with various concentrations, and gels can form in PI/NMP solution with a suitable concentration or at a low temperature. Gel–sol transition in the PI/NMP solution has been investigated through a combination of polarized optical microscope, differential scanning calorimeter measurement, and rheological measurements. According to Winter–Chambon theory, the critical gel point is 12 wt %, and the loss tangent (tan δ) shows frequency independence. Gel–sol transition temperature (T_gel) for the 13 wt % solution is around 65 °C. Below the T_gel, the gel exhibits strong optical planar texture, indicating the formation of a fully anisotropic phase, which has a great importance for the fabrication of PI fibers by gel‐spinning. Dynamic temperature sweep measurements show that the formation of the gel from solution is thermoreversible and is significantly delayed in the cooling process. Under the favorable conditions, the tensile strength and modulus of the fibers derived from the solution are about 0.7 and 12.5 GPa using gel‐spinning method, which is believed to afford broad application potential in preparing high‐performance PI fibers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 450–459     

Supramolecular polymer gels formed from carboxy‐terminated telechelic polybutadiene and polyamidine through amidinium‐carboxylate salt bridge

In this article, we report the preparation and properties of the bulk supramolecular polymer gels prepared from a polybutadiene based on the amidinium‐carboxylate salt bridge, highlighting the difference from a well‐established network system based on carboxylic acid and amine. We have prepared the amidinium‐carboxylate salt bridge‐based supramolecular polymer gels from a carboxy‐terminated telechelic polybutadiene and a linear polyamidine having N,N′‐di‐substituted acetamidine group in the main chain. FTIR analysis along with Small angle X‐ray scattering measurements indicated that the salt bridge was attributed to the gelation through three‐dimensional network formation. Virtually no fluidity was observed for the supramolecular gel containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at room temperature and a T_gel of 37 °C. For comparison, the supramolecular polymer gels crosslinked by ammonium‐carboxylate salt were prepared using a linear polyethyleneimine instead of the polyamidine. The gel with equimolar amounts of the carboxyl group and the secondary amino group showed liquid‐like fluidity with a G′ value of about 0.01 MPa at room temperature, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form without salt formation, as evidenced by FTIR analysis. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1815–1824     

Synthesis of biotin‐tagged chemical cross‐linkers and their applications for mass spectrometry

Chemical cross‐linking combined with mass spectrometry (MS) has been used to elucidate protein structures and protein‐protein interactions. However, heterogeneity of the samples and the relatively low abundance of cross‐linked peptides make this approach challenging. As an effort to overcome this hurdle, we have synthesized lysine‐reactive homobifunctional cross‐linkers with the biotin in the middle of the linker and used them to enrich cross‐linked peptides. The reaction of biotin‐tagged cross‐linkers with purified HIV‐1 CA resulted in the formation of hanging and intramolecular cross‐links. The peptides modified with biotinylated cross‐linkers were effectively enriched and recovered using a streptavidin‐coated plate and MS‐friendly buffers. The enrichment of modified peptides and removal of the dominantly unmodified peptides simplify mass spectra and their analyses. The combination of the high mass accuracy of Fourier transform ion cyclotron resonance (FT‐ICR) MS and the tandem mass spectrometric (MS/MS) capability of the linear ion trap allows us to unambiguously identify the cross‐linking sites and additional modification, such as oxidation. Copyright © 2009 John Wiley & Sons, Ltd.     

Antimicrobial agents as photostabilizers for rigid poly(vinyl chloride)

Some amide derivatives of ethylene glycol‐bis(2‐aminoethylether)‐N,N,N^′,N^′‐tetraacetic acid (EGTA) have been prepared via their coupling with different aniline derivatives: amino, methyl, chloro, and hydroxy aniline. The EGTA amide derivatives were characterized, and their antimicrobial activities were evaluated. These antimicrobial agents have been investigated as photostabilizers for rigid poly(vinyl chloride) (PVC), suspension PVC, with a K value of 70. Their stabilizing efficiencies were evaluated by determining the percentage of weight loss, the intrinsic viscosities, as well as the amount of formed gel of the photodegraded PVC. The extent of discoloration and the change in the mechanical properties of the photodegraded polymer were also evaluated. The applied materials reduced the loss in weight that resulted from HCl evolution during photodegradation. Both viscosity and gel content measurements showed also a decrease in their values during the degradation process. The decrease in the percentage of gel formation upon applying the investigated photostabilizers reflects the lowering in extent of cross‐linking of the polymer, which implies preserving the mechanical properties of PVC. The extent of discoloration was also improved in the presence of the investigated compounds. The results have proved a greater stabilizing efficiencies of the antimicrobial EGTA amide derivatives than that of the phenyl salicylate ultraviolet (UV) absorber, which is commonly used as an industrial stabilizer. A radical mechanism was proposed to account for the stabilizing action of the investigated products. Copyright © 2011 John Wiley & Sons, Ltd.     

Immobilization of Thienyl-Containing Azo Pigments on Silica Gel Surface

Reactions of chlorinated silica gel with thienyllithium and its derivatives gave silica gels modified by organic fragments. By successive chemical transformations of the latter immobilized thienyl-contaning azo pigments were obtained. Azo pigments can also be immobilized on silica gel surface through reactions with 2,4,6-trichloro-1,3,5-triazine. Silica gels with grafted azo pigments are characterized by high resistance to light and washing.     

Formation of junction zones in thermoreversible methylcellulose gels

To analyze the structure of junction zones formed in methylcellulose (MC) gel, the modified Eldridge–Ferry method was applied to phase diagrams for aqueous solutions of different molecular weight MCs derived from micro‐DSC, small‐angle X‐ray scattering, and visual inspection. The results suggested that junctions in MC gels took thin, rodlike fringed‐micellar crystallites. The junction multiplicity s decreased from 4.3 for low‐temperature melting gels to 2.0 for high‐temperature melting gels. With increasing molecular weight, the number ζ of statistical units in a junction along a single chain increased from 27 to 54. Because the number depends sensitively on the enthalpy of bonding per mole of the repeat units of MC, our estimate is considered to give an upper bound to the junction length. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 943–946, 2001     

PH-Responsive and Self-Healing Hydrogels Fabricated with Guar Gum and Reactive Microgels

Hydrogels (MR gels) with pH-responsive and self-healing properties were prepared via guar gum solutions and reactive microgel. The reactive microgel was characterized through scanning electron microscope (SEM), laser particle-size analysis measurements, and FTIR. Compared with general hydrogels cross-linked by borax (B gels), the MR gels exhibit superior properties on the aspects of viscosity, viscoelasticies, and temperature resistance. Furthermore, the viscosities of MR gels increase with the rising pH value, and it can dynamically reconstruct after being destructed by external force. In addition, the microstructure of the MR gel was characterized by SEM, which confirms that the reactive microgel indeed as cross-linker and each microgel can cross-link several chains as if the chains were grafting from the microgels. These features show that the addition of reactive microgels can enhance the strength of MR gels significantly and indicate that the MR gels have a great potential application in hydraulic fracturing, especially in high-temperature oil fields.     

Coreflooding and Pore-Scale Visualization of Foamed Gel Flowed in Porous Network Media

To investigate the mechanisms of enhancing oil recovery and the flow behaviors of foamed gel in porous media, foamed gels with characteristics of excellent strength and viscosity were prepared with polymer, crosslinking agent, foam agent, and formation water. The breakthrough-vacuum method and a rotary viscometer were used to evaluate the strength and viscosity of foamed gel. Coreflooding and pore-level visualization experiments were performed in heterogeneous reservoir models. Laboratory results illustrate that high strength and viscosity of foamed gel can be prepared by 0.15% NJ-8, 0.2% polyacrylamide solution, and 1.5% foaming agent. The strength and viscosity of the foamed gel reached 0.06 MPa and 10,000 MPa · s, respectively. The results of coreflooding experiments in heterogeneous cores show that oil recovery can be improved by approximately 36.9% after injecting 0.3 pore volume of the foamed gel, and enhanced oil recovery is mainly attributed to the improving sweep efficiency of mid- to low-permeability layers. Images of visualization flooding demonstrate that foamed gel exhibits good oil resistance and elasticity when used with crude oil. Furthermore, the new amoeba effect, Jamin effect, fluid-diverting effect, and extruding effect between foamed gel and oil in porous media can enhance oil recovery by improving sweep efficiency.