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The industrial application of pea protein is limited due to its poor gelation properties. This study aimed to evaluate the effects of psyllium husk powder (PHP) on improving the rheological, textural, and structural properties of heat-induced pea protein isolate (PPI) gel. Scanning electron microscopy (SEM), intermolecular forces analysis, the quantification of the surface hydrophobicity and free amino groups, and Fourier transform infrared spectroscopy (FTIR) were conducted to reveal the inner structures of PPI-PHP composite gels, conformational changes, and molecular interactions during gelation, thereby clarifying the underlying mechanism. The results showed that moderate levels of PHP (0.5–2.0%) improved the textural properties, water holding capacity (WHC), whiteness, and viscoelasticity of PPI gel in a dose-dependent manner, with the WHC (92.60 ± 1.01%) and hardness (1.19 ± 0.02 N) peaking at 2.0%. PHP significantly increased surface hydrophobicity and enhanced hydrophobic interactions, hydrogen bonding, and electrostatic interactions in PPI-PHP composite gels. Moreover, the electrostatic repulsion between anionic PHP and negatively charged PPI in a neutral environment prevented the rapid and random aggregation of proteins, thereby promoting the formation of a well-organized gel network with more β-sheet structures. However, the self-aggregation of excessive PHP (3.0%) weakened molecular interactions and disrupted the continuity of protein networks, slightly reducing the gel strength. Overall, PHP emerged as an effective natural gel enhancer for the production of pea protein gel products. This study provides technical support for the development of innovative plant protein-based foods with strong gel properties and enriched dietary fiber content. [ABSTRACT FROM AUTHOR]

A novel fire-preventing composite gel, mainly made from steel slag (SS) and silica fume (SF), was created for a coal mine’s spontaneous combustion. The gelation mechanism of the steel slag-based composite gel (SSG) was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (SEM). The findings suggest that SSG is generated through the processes of hydration and geopolymerization involving SS and SF. And in the alkaline milieu of a 1.5 M water glass solution, SSG manifests enhanced strength and water retention capacities. Moreover, the fire prevention and extinguishing performance of the SSG was analyzed and verified using low-temperature oxidation, thermogravimetry, and low temperature nitrogen adsorption experiment (LTNA). The SSG has proven highly effective in suppressing spontaneous coal combustion by inhibiting CO production, raising the coal oxidation temperature, and reducing the contact area between oxygen and the coal body.

Gelation, an important quality attribute of meat products, significantly influences the appearance, flavor, and texture of meat products. Enhancing gelation in meat products holds immense importance in improving the production process and the quality. The gel properties of meat products are influenced by the content and structure of protein aggregates and the aggregation rate during processing. Protein additives have the potential to partially replace myofibrillar proteins in gelation and emulsification properties, leading to cost reduction, and therefore have attracted much research interest for the development of new meat products and the optimization of the processing technology. This paper summarizes recent studies on the gelation mechanism of myofibrillar proteins, and reviews the properties and applications of the major protein additives as well as recent progress in using protein additives combined with polysaccharide colloids, enzymes or phosphates to enhance the gelation of meat products. This review may serve as a valuable reference for enhancing the quality of gel-type meat products.

To investigate the effect of the chemical composition of a metal–organic crosslinker on the performances of fracturing fluid in high-temperature conditions, four zirconium (Zr) crosslinkers and one aluminum–zirconium (Al-Zr) crosslinker with a polyacrylamide were used. The crosslinkers possessed the same Zr concentration, but they differed in component amounts and the order of the addition of the crosslinker components, leading to different chemical compositions in the crosslinkers. The fracturing fluids prepared by different tested crosslinkers were compared in terms of properties of rheological behavior, sand-carrying ability, microstructure, and gel breaking characteristics. The results showed that the fracturing fluids prepared by zirconium lactic acid, ethanediamine, and sorbitol crosslinkers offered the slowest viscosity development and highest final viscosity compared to the zirconium lactic acid crosslinker and the zirconium lactic acid and ethanediamine crosslinker. The zirconium sorbitol, lactic acid, and ethanediamine crosslinker exhibited a faster crosslinking rate and a higher final viscosity than the zirconium lactic acid, ethanediamine, and sorbitol crosslinker; the crosslinker showed crosslinking density and crosslinking reactivity, resulting in more crosslinking sites and a higher strength in the fracturing fluid. The Al-Zr-based crosslinker possessed better properties in temperature and shear resistance, viscoelasticity, shear recovery, and sand-carrying ability than the Zr-based crosslinker due to the synergistic crosslinking effect of aluminum and zirconium ions. The tertiary release gelation mechanism of the Al-Zr-based fracturing fluid achieved a temperature resistance performance in the form of continuous crosslinking, avoiding the excessive crosslinking dehydration and reducing viscosity loss caused by early shear damage. These results indicated that the chemical compositions of metal–organic crosslinkers were important factors in determining the properties of fracturing fluids. Therefore, the appropriate type of crosslinker could save costs without adding the additional components required for high-temperature reservoirs. [ABSTRACT FROM AUTHOR]

The objective of this study is to enhance the comprehension of the mechanism of enzymatic gelation in milk by investigating statistically significant changes in milk viscosity and carrying out corresponding electron microscopic studies of the process of structure formation at the enzymatic stage of coagulation using various enzyme preparations. Employing a non-destructive method (Hot-Wire) to monitor viscosity, we were able to confirm a decrease in viscosity during the middle of this stage and identify a previously undescribed peak in viscosity change at the end of the enzymatic stage. By conducting parallel studies utilizing transmission electron microscopy and various methods of specimen preparation, it was possible to discover that a hierarchical transformation process in the protein component of milk started at the end of the enzymatic stage of gelation in milk. This process is triggered by a cooperative conformational transition in casein micelle clusters, which leads to a series of increasingly energy-intensive reactions resulting in the transformation of loosely bound micelle clusters into denser aggregates. The final structure of the milk gel primarily consists of the previously formed individual micelle aggregates. It was noted that no changes in the microstructure of the milk gel were observed during the enzymatic stage of gelation when milk-clotting enzymes (MCEs) of animal, plant, and microbial (GMO) origins were used. Furthermore, investigations into the molecular weight distribution of soluble protein substances in samples generated with different types of MCEs revealed that the enzyme derived from the fungi of Rhizomucor miehei had a greater proteolytic effect on milk proteins compared to other variants of MCEs. [ABSTRACT FROM AUTHOR]

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study is to enhance the comprehension of the mechanism of enzymatic gelation in milk by visualizing the evolution of its microstructure through transmission electron microscopy. In order to minimize the potential for artifacts during the preparation process and eliminate any possible difficulties in interpreting the resulting images, three distinct methods were employed in the research: shading the surface topography with vacuum deposition of heavy metal, negative staining of the specimen with a heavy metal solution and replicating a cleavage of a quick-frozen sample. The selection of time intervals for sampling the gel during its evolution is determined by the most probable significant modifications in the resulting gel. Based on the research, it has been shown that natural milk is a nonequilibrium system from the perspective of statistical thermodynamics. A notable observation is that the glycomacropeptides forming the hair layer on the surface of casein micelles are unevenly distributed, leading to the formation of micelle dimers and trimers. It has been determind that during the initial stage of enzymatic gelation in milk, clusters of loosely bound micelles are formed in areas with the highest concentration. The formation of micelle chains is absent at this stage due to the non-anisometric nature of micelles and the energetic disadvantage of their formation. It has been found that under the influence of enzymatic gelation near the gel point, a hierarchical process involving the transformation of the milk’s protein component is activated. The trigger mechanism for this process is a cooperative conformational transition in clusters of casein micelles, which initiates a chain of more energy-intensive reactions in the following sequence: hydro­phobic interactions → hydrogen bridges → electrostatic interactions → calcium bridges. The result is the conversion of loosely bound micelle clusters into denser aggregates, predominantly contributing to the formation of milk curd. It is worth noting that gelation in milk can be regarded as a process that reduces the free energy of the dispersed system. Understanding the correlation between the decrease in the free energy value during gelation and the physical properties of the finished cheese and other dairy products continues to be a relevant area of research.

The industrial application of pea protein is limited due to its poor gelation properties. This study aimed to evaluate the effects of psyllium husk powder (PHP) on improving the rheological, textural, and structural properties of heat-induced pea protein isolate (PPI) gel. Scanning electron microscopy (SEM), intermolecular forces analysis, the quantification of the surface hydrophobicity and free amino groups, and Fourier transform infrared spectroscopy (FTIR) were conducted to reveal the inner structures of PPI-PHP composite gels, conformational changes, and molecular interactions during gelation, thereby clarifying the underlying mechanism. The results showed that moderate levels of PHP (0.5–2.0%) improved the textural properties, water holding capacity (WHC), whiteness, and viscoelasticity of PPI gel in a dose-dependent manner, with the WHC (92.60 ± 1.01%) and hardness (1.19 ± 0.02 N) peaking at 2.0%. PHP significantly increased surface hydrophobicity and enhanced hydrophobic interactions, hydrogen bonding, and electrostatic interactions in PPI-PHP composite gels. Moreover, the electrostatic repulsion between anionic PHP and negatively charged PPI in a neutral environment prevented the rapid and random aggregation of proteins, thereby promoting the formation of a well-organized gel network with more β-sheet structures. However, the self-aggregation of excessive PHP (3.0%) weakened molecular interactions and disrupted the continuity of protein networks, slightly reducing the gel strength. Overall, PHP emerged as an effective natural gel enhancer for the production of pea protein gel products. This study provides technical support for the development of innovative plant protein-based foods with strong gel properties and enriched dietary fiber content.

To investigate the effect of K+ on the properties and mechanism of the composite gel system consisting of tamarind gum and κ-carrageenan, four methods including rheology, texture analysis, microstructure, and infrared spectroscopy were used to investigate the properties and structure of the composite gel with different K+ additions. The rheological results showed that the addition of K+ increased the modulus of the gel system and decreased the compliance and total deformation. When the addition of K+ increased to 15 mmol/L, the apparent viscosity reached its highest value of 2690 Pa·s. The results of texture analysis revealed that the strength and hardness of the gel system increased with the addition of K+, but its elasticity and cohesiveness decreased relatively. Infrared spectroscopy and microstructure demonstrated that K+ could promote the interaction between tamarind gum and κ-carrageenan, the gel pores tend to be dense and uniform, and the inter-pore walls were most regular and strong at the K+ addition of 15 mmol/L. The results showed that the addition of K+ could make the gel system exhibit better viscoelasticity and anti-deformation, and make the network structure more compact, which would provide a theoretical reference for the application of tamarind gum and κ-carrageenan in compounding.

To investigate the effect of the chemical composition of a metal–organic crosslinker on the performances of fracturing fluid in high-temperature conditions, four zirconium (Zr) crosslinkers and one aluminum–zirconium (Al-Zr) crosslinker with a polyacrylamide were used. The crosslinkers possessed the same Zr concentration, but they differed in component amounts and the order of the addition of the crosslinker components, leading to different chemical compositions in the crosslinkers. The fracturing fluids prepared by different tested crosslinkers were compared in terms of properties of rheological behavior, sand-carrying ability, microstructure, and gel breaking characteristics. The results showed that the fracturing fluids prepared by zirconium lactic acid, ethanediamine, and sorbitol crosslinkers offered the slowest viscosity development and highest final viscosity compared to the zirconium lactic acid crosslinker and the zirconium lactic acid and ethanediamine crosslinker. The zirconium sorbitol, lactic acid, and ethanediamine crosslinker exhibited a faster crosslinking rate and a higher final viscosity than the zirconium lactic acid, ethanediamine, and sorbitol crosslinker; the crosslinker showed crosslinking density and crosslinking reactivity, resulting in more crosslinking sites and a higher strength in the fracturing fluid. The Al-Zr-based crosslinker possessed better properties in temperature and shear resistance, viscoelasticity, shear recovery, and sand-carrying ability than the Zr-based crosslinker due to the synergistic crosslinking effect of aluminum and zirconium ions. The tertiary release gelation mechanism of the Al-Zr-based fracturing fluid achieved a temperature resistance performance in the form of continuous crosslinking, avoiding the excessive crosslinking dehydration and reducing viscosity loss caused by early shear damage. These results indicated that the chemical compositions of metal–organic crosslinkers were important factors in determining the properties of fracturing fluids. Therefore, the appropriate type of crosslinker could save costs without adding the additional components required for high-temperature reservoirs.

Various polymers are the most widely used product to provide rheology for water-based fracturing fluid, however, they have weaknesses in terms of temperature resistance and salt resistance. The change from organic-based to inorganic thickeners may be a meaningful attempt. Inorganic silica gel is a potentially alternative viscosifier with high temperature resistance, excellent proppant carrying capacity, and can even be used to prepare fracturing fluids with high salinity of produced water. In this paper, the silica gel viscosifier was firstly prepared using sol–gel method. Then, the gelation time under different influencing factors and rheological properties of the silica gel viscosifier were studied in detail. Subsequently, the silica gel-based fracturing fluid was prepared by adding the desired amount of drag reducer to the silica sol solution, and the properties of novel fracturing fluid were systematically evaluated with regard to the temperature and shearing resistance, drag reduction, and static proppant suspension. The potential mechanism of gelation process by syneresis of silica gel was revealed at last. Results showed that the microstructure of silica gel is synthetic, amorphous and consists of a three-dimensional network of SiO2 particles. The effect of SiO2 concentration on the gelation time is more pronounced than other factors such as temperature and pH level. In addition, the silica gel viscosifier exhibits strong salt resistance, whether monovalent ions (Na+, K+) or divalent ions (Ca2+, Mg2+), and the gelation time decreased significantly with the increase of salt concentration. The shear viscosity of the silica gel viscosifier increased with an increase of SiO2 concentration, showing shear thinning behavior as well. Meanwhile, the silica gel-based fracturing fluid prepared by adding drag reducer into silica sol solution also presented excellent thermal stability and shear resistance, drag reduction and proppant suspension performances. The retained viscosity can be maintained above 50 mPa·s after shearing at 180 °C for 60 mins; the drag reduction rate shows a declining trend at high displacement due to the gelation process; the settling rate of 40/70 mesh sand proppant with 35 % sand ratio is less than 30 % after standing at 90 °C for 4 h. In addition, the gelation process is essentially the formation of Si-O-Si linkage by dehydration between SiO2 particles, which is gradually extended at both ends and sides of the chain, and eventually forms a rigid, highly porous, entangled network. Findings found in this study provide a research basis for the popularization and application of silica gel-based fracturing fluid.

To expand the applicability of gel fracturing fluids in ultra-high-temperature reservoirs, a temperature-resistant polymer was synthesized using the solution polymerization method. Subsequently, an ultra-high-temperature-resistant polymer gel was formulated by incorporating an organic zirconium crosslinking agent. A comprehensive investigation was carried out to systematically study and evaluate the steady shear property, dynamic viscoelasticity, and temperature and shear resistance performance, as well as the core damage characteristics of the polymer gel. The obtained results demonstrate that the viscosity remained at 147 mPa·s at a temperature of 200 °C with a shear rate of 170 s−1. Compared with the significant 30.9% average core damage rate observed in the guanidine gum fracturing fluid, the core damage attributed to the polymer gel was substantially mitigated, measuring only 16.6%. Finally, the gelation mechanism of the polymer gel was scrutinized in conjunction with microscopic morphology analysis. We expect that this study will not only contribute to the effective development of deep and ultradeep oil and gas reservoirs but also furnish a theoretical foundation for practical field applications. [ABSTRACT FROM AUTHOR]

So far, it has been difficult to directly compare diverse characteristic gelation mechanisms over different length and time scales. This paper presents a universal water structure analysis of several gels with different structures and gelation mechanisms including polymer gels, supramolecular gels composed of surfactant micelles, and cement gels. The spatial distribution of water molecules was analyzed at molecular level from a diagram of the relaxation times and their distribution parameters (τ–β diagrams) with our database of the 10 GHz process for a variety of aqueous systems. Polymer gels with volume phase transition showed a small decrease in the fractal dimension of the hydrogen bond network (HBN) with gelation. In supramolecular gels with rod micelle precursor with amphipathic molecules, both the elongation of the micelles and their cross-linking caused a reduction in the fractal dimension. Such a reduction was also found in cement gels. These results suggest that the HBN inevitably breaks at each length scale with relative increase in steric hindrance due to cross-linking, resulting in the fragmentation of collective structures of water molecules. The universal analysis using τ–β diagrams presented here has broad applicability as a method to characterize diverse gel structures and evaluate gelation processes. [ABSTRACT FROM AUTHOR]

This article reviews different studies on the gelation mechanisms and network structural characteristics in polysaccharide gels at the different length scales of observation: macroscopic, microscopic, and molecular. Rheological and micro-DSC (Differential Scanning Calorimetry) measurements represent the macroscopic viewpoints on the gelation of pure kappa-carrageenan (KC), iotacarrageenan (IC) and KC/IC mixtures. Microscopic rheological properties observed using particle tracking experiments have been used to elucidate the formation of heterogeneous networks of KC-rich and IC-rich domains in mixed KC/IC gels, and facilitate observations of their aging process. Nuclear magnetic resonance (NMR) relaxation time measurements provide information on the tumbling motion and local mobility; these molecular-level experiments are presented for agar, agarose, native gellan and deacylated gellan chains. NMR diffusion measurements of gelling and probe polymers give insights into the conformational changes, aggregation and network formation, and aging mechanisms, and are presented for all studied polysaccharides. [ABSTRACT FROM AUTHOR]

In this paper, the gel properties of sodium alginate with Y3+, Ce3+, La3+ and Er3+ were studied. By studying the mechanical properties, equilibrium water content, ion exchange rate and gel mechanism of seaweed rare earth gel, it was found that: The coordination form of rare earth ions and carboxyl group in sodium alginate was pseudo-bridged monodentate coordination and bridge coordination. At the same time, the special three-dimensional network structure of the rare earth gel was formed through the planar and non-planar geometry formed by intramolecular and intermolecular chelation, and the gel strength of the gel formed by La3+, Y3 +, Er3+, Ce3+ and sodium alginate M/G≈1 was between 32 and 41 N, the Young’s modulus was between 14 and 20 N, the elasticity was between 55% and 59%, the equilibrium water content was greater than 93%, the strength of the four gel was Ce3+> Er3+> Y3+> La3+, the elasticity was Ce3+1, the affinity of seaweed rare earth gel was in this order：Er3+>Ce3+>Y3+>La3+. When M/G=0.99≈1 and M/G=0.19 Er3+> Y3+> La3+. Among them, Ce3+, Y3+ and La3+ had a certain preference for G fragment of sodium alginate, and Er3+ had a certain preference for M fragment. This study would lay a theoretical foundation for the intensive processing and utilization of sodium alginate and the development of new functional materials of rare earth elements.

Highlights Metal–organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels. The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents. Abstract The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe3O4@C/rGO and Ni-doped Fe3O4@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (− 58.1 dB and 6.48 GHz) and 2.8 mm (− 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

A novel fire-preventing composite gel, mainly made from steel slag (SS) and silica fume (SF), was created for a coal mine's spontaneous combustion. The gelation mechanism of the steel slag-based composite gel (SSG) was investigated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (SEM). The findings suggest that SSG is generated through the processes of hydration and geopolymerization involving SS and SF. And in the alkaline milieu of a 1.5 M water glass solution, SSG manifests enhanced strength and water retention capacities. Moreover, the fire prevention and extinguishing performance of the SSG was analyzed and verified using low-temperature oxidation, thermogravimetry, and low temperature nitrogen adsorption experiment (LTNA). The SSG has proven highly effective in suppressing spontaneous coal combustion by inhibiting CO production, raising the coal oxidation temperature, and reducing the contact area between oxygen and the coal body. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of oat β-glucan on the formation mechanism, microstructure and physicochemical properties of konjac glucomannan (KGM) composite hydrogel. The dynamic rheology results suggested that the addition of oat β-glucan increased the viscoelastic modulus of the composite hydrogel, which was conducive to the formation of a stronger gel network. Gelling force experiments showed that hydrogen bonds and hydrophobic interactions participated in the formation of the gel network. Textural profile analysis results found that the amount of oat β-glucan was positively correlated with the elasticity, cohesiveness and chewiness of the composite hydrogel. The water-holding capacity of the composite hydrogel was enhanced significantly after the addition of oat β-glucan (p < 0.05), which was 18.3 times that of the KGM gel. The thermal stability of KGM gel was enhanced after the addition of oat β-glucan with the increase in Tmax being approximately 30 °C. Consequently, a composite hydrogel based on KGM and oat β-glucan was a strategy to overcome pure KGM gel shortcomings. [ABSTRACT FROM AUTHOR]

Highlights: Metal–organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels. The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents. The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal–organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal–oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe3O4@C/rGO and Ni-doped Fe3O4@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (− 58.1 dB and 6.48 GHz) and 2.8 mm (− 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA. [ABSTRACT FROM AUTHOR]

To expand the applicability of gel fracturing fluids in ultra-high-temperature reservoirs, a temperature-resistant polymer was synthesized using the solution polymerization method. Subsequently, an ultra-high-temperature-resistant polymer gel was formulated by incorporating an organic zirconium crosslinking agent. A comprehensive investigation was carried out to systematically study and evaluate the steady shear property, dynamic viscoelasticity, and temperature and shear resistance performance, as well as the core damage characteristics of the polymer gel. The obtained results demonstrate that the viscosity remained at 147 mPa·s at a temperature of 200 °C with a shear rate of 170 s−1. Compared with the significant 30.9% average core damage rate observed in the guanidine gum fracturing fluid, the core damage attributed to the polymer gel was substantially mitigated, measuring only 16.6%. Finally, the gelation mechanism of the polymer gel was scrutinized in conjunction with microscopic morphology analysis. We expect that this study will not only contribute to the effective development of deep and ultradeep oil and gas reservoirs but also furnish a theoretical foundation for practical field applications.

Silk fibroin hydrogel not only has biocompatibility, but also has environmental response ability. It plays an important role in the development of material. The gelation mechanism of silk fibroin hydrogel is very important to textile and medicine fields. The molecular dynamics simulation was used to discuss the structure and non-bond interaction of silk fibroin hydrogel. The results show that the non-bond interactions between silk fibroin molecules and water molecules have certain influence on the formation of silk fibroin hydrogel. According to the hydrogen bond analysis, the hydrogen bonds are mainly formed between random coil peptide fragments at the two ends of silk fibroin molecules and residues 252-254 are the key residues. The electrostatic and polar solvation interactions between silk fibroin molecules plays a major role in cross-linking of the coil segments of two silk fibroin molecules.

So far, it has been difficult to directly compare diverse characteristic gelation mechanisms over different length and time scales. This paper presents a universal water structure analysis of several gels with different structures and gelation mechanisms including polymer gels, supramolecular gels composed of surfactant micelles, and cement gels. The spatial distribution of water molecules was analyzed at molecular level from a diagram of the relaxation times and their distribution parameters (τ–β diagrams) with our database of the 10 GHz process for a variety of aqueous systems. Polymer gels with volume phase transition showed a small decrease in the fractal dimension of the hydrogen bond network (HBN) with gelation. In supramolecular gels with rod micelle precursor with amphipathic molecules, both the elongation of the micelles and their cross-linking caused a reduction in the fractal dimension. Such a reduction was also found in cement gels. These results suggest that the HBN inevitably breaks at each length scale with relative increase in steric hindrance due to cross-linking, resulting in the fragmentation of collective structures of water molecules. The universal analysis using τ–β diagrams presented here has broad applicability as a method to characterize diverse gel structures and evaluate gelation processes.

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study was to evaluate the effect of oat β-glucan on the formation mechanism, microstructure and physicochemical properties of konjac glucomannan (KGM) composite hydrogel. The dynamic rheology results suggested that the addition of oat β-glucan increased the viscoelastic modulus of the composite hydrogel, which was conducive to the formation of a stronger gel network. Gelling force experiments showed that hydrogen bonds and hydrophobic interactions participated in the formation of the gel network. Textural profile analysis results found that the amount of oat β-glucan was positively correlated with the elasticity, cohesiveness and chewiness of the composite hydrogel. The water-holding capacity of the composite hydrogel was enhanced significantly after the addition of oat β-glucan (p < 0.05), which was 18.3 times that of the KGM gel. The thermal stability of KGM gel was enhanced after the addition of oat β-glucan with the increase in Tmax being approximately 30 °C. Consequently, a composite hydrogel based on KGM and oat β-glucan was a strategy to overcome pure KGM gel shortcomings.

A novel and simple gelling system based on a water-soluble copolymer of isobutylene and maleic anhydride (commercial name, Isobam) was adopted to manufacture various ceramics via spontaneous gelation. The gelation mechanism of AlN slurry was investigated using infrared spectroscopy. Results show that Isobam was hydrolyzed to produce the –COOH group, and the hydrogen bonding was formed between the –COOH and –CONH 2 groups of Isobam during spontaneous gelation. Meanwhile, the gelling process of the Isobam system could be accelerated via enhancing hydrogen bonding through APS addition. With 1 wt% addition of APS, the gelation time reduced to 23 h, the viscosity of 50 vol% AlN slurry decreased to 0.21 Pa·s, and the flexural strength of green body improved by 48%. Therefore, the presence of hydrogen bonding in the Isobam gelation mechanism was confirmed, and it could be enhanced by introducing APS to accelerate gelation. [ABSTRACT FROM AUTHOR]

Sodium silicate solutions, also known as waterglass, have been found to have remarkable utility in a variety of applications. The cumulative weight of evidence from 70 years of varied analysis indicates that silicate solutions consist of a wide range of species, from monomers through oligomers, up to colloids. Moreover, the structure and distribution of these species are greatly dependent upon many parameters, such as solute concentrations, silica to alkali ratio, pH, and temperature. The most interesting and characteristic property of silicate solutions is their ability to form silica gels. Overall, despite extensive research using different spectroscopic and scattering techniques, many questions related to sodium silicate's dynamic structure, stability, polymerization, and gelation remain difficult to answer. The multitude of simultaneous reactions which restructure the silicate species at the atomic scale in response to variation in solution and environmental parameters, makes it difficult to investigate the individual events using only experimental data. Molecular modelling provides an alternative way to study the unknown areas in the aqueous silicate and silica gel systems, generating key insights into the chemical reactions at microscopic length scales. However, sufficient sampling remains a challenge for the practical use of molecular simulation for these systems. Based on both experimental and modelling studies, this review provides a detailed discussion over the structure and speciation of sodium silicate solutions, their gelation mechanism and kinetics, and the syneresis phenomenon. The goal is not only to review the current level of understanding of sodium silicate solutions, silica gels and characterization techniques suitable for studying them, but also to identify the gaps in the literature and open up opportunities for advancing knowledge about these complex systems. We believe that the future direction of research should be toward correlating atomistic, molecular, and meso-scale level details of interactions and reactions in silicate solution and establishing a fundamental understanding of its gelation mechanism and kinetics. We believe that this knowledge could eliminate the "trial and error" approach in manufacturing, and improve structural control in the synthesis of important materials derived from these solutions, such as silica gels and zeolites. [Display omitted] • Review of factors affecting sodium silicate solution's speciation and gelation. • Visualization of chemical structure of sodium silicate solutions and gels. • A general theory of silica gelation modified for sodium silicate solutions. • Molecular modelling provides atomistic insight into complex silica-water reactions. • Insights illustrate the need to advance our understanding of silica-water systems. [ABSTRACT FROM AUTHOR]

Various polymers are the most widely used product to provide rheology for water-based fracturing fluid, however, they have weaknesses in terms of temperature resistance and salt resistance. The change from organic-based to inorganic thickeners may be a meaningful attempt. Inorganic silica gel is a potentially alternative viscosifier with high temperature resistance, excellent proppant carrying capacity, and can even be used to prepare fracturing fluids with high salinity of produced water. In this paper, the silica gel viscosifier was firstly prepared using sol–gel method. Then, the gelation time under different influencing factors and rheological properties of the silica gel viscosifier were studied in detail. Subsequently, the silica gel-based fracturing fluid was prepared by adding the desired amount of drag reducer to the silica sol solution, and the properties of novel fracturing fluid were systematically evaluated with regard to the temperature and shearing resistance, drag reduction, and static proppant suspension. The potential mechanism of gelation process by syneresis of silica gel was revealed at last. Results showed that the microstructure of silica gel is synthetic, amorphous and consists of a three-dimensional network of SiO 2 particles. The effect of SiO 2 concentration on the gelation time is more pronounced than other factors such as temperature and pH level. In addition, the silica gel viscosifier exhibits strong salt resistance, whether monovalent ions (Na+, K+) or divalent ions (Ca2+, Mg2+), and the gelation time decreased significantly with the increase of salt concentration. The shear viscosity of the silica gel viscosifier increased with an increase of SiO 2 concentration, showing shear thinning behavior as well. Meanwhile, the silica gel-based fracturing fluid prepared by adding drag reducer into silica sol solution also presented excellent thermal stability and shear resistance, drag reduction and proppant suspension performances. The retained viscosity can be maintained above 50 mPa·s after shearing at 180 °C for 60 mins; the drag reduction rate shows a declining trend at high displacement due to the gelation process; the settling rate of 40/70 mesh sand proppant with 35 % sand ratio is less than 30 % after standing at 90 °C for 4 h. In addition, the gelation process is essentially the formation of Si-O-Si linkage by dehydration between SiO 2 particles, which is gradually extended at both ends and sides of the chain, and eventually forms a rigid, highly porous, entangled network. Findings found in this study provide a research basis for the popularization and application of silica gel-based fracturing fluid. [ABSTRACT FROM AUTHOR]

In this work, the gelation mechanism of graphene quantum dots (GQDs) into hydrogels is investigated using dynamic light scattering and ultraviolet-visible techniques. Hydrogels are prepared through the hydrothermal reduction of concentrated GQDs solutions (20–50 mg/mL) using l -ascorbic acid as the reducing agent. At early stages of the gelation process (first 2 h), J-type aggregation of GQDs results in the formation of particles with dimensions around 10 nm. As the gelation process proceeds, formation of larger particles through the aggregation of almost all GQDs results in slower dynamics and hindered Brownian motions in the solution. With the reduction of a majority of edge-carboxyl groups through six first hours of the hydrothermal process, a change in the self-assembly mechanism takes place (from J-type to H-type). A GQDs hydrogel, with an interconnected colloidal morphology and a very low density (~0.009 g/cm 3 ) can be obtained after 8 h of the hydrothermal process. The specific surface area of the prepared GQDs hydrogel, fabricated through the hydrothermal reduction of the 20 mg/mL GQDs precursor solution, is >1000 m 2 /g. Hydrogels and cryogels prepared using GQDs as the building units can be applicable where hyper-porous structures with large number of available sites are needed. [ABSTRACT FROM AUTHOR]

Chitosan colloidal systems, created by dispersing in aqueous solutions of hydrochloric acid, with and without the addition of disodium β-glycerophosphate (β-NaGP), were prepared for the investigation of forming mechanisms of chitosan hydrogels. Three types of chitosan were used in varying molecular weights. The impacts of the charge and shape of the macromolecules on the phase transition process were assessed. The chitosan system without the addition of β-NaGP was characterized by stiff and entangled molecules, in contrast to the chitosan system with the addition of β-NaGP, wherein the molecules adopt a more flexible and disentangled form. Differences in molecules shapes were confirmed using the Zeta potential and thixotropy experiments. The chitosan system without β-NaGP revealed a rapid nature of phase transition-consistent with diffusion-limited aggregation (DLA). The chitosan system with β-NaGP revealed a two-step nature of phase transition, wherein the first step was consistent with reaction-limited aggregation (RLA), while the second step complied with diffusion-limited aggregation (DLA). [ABSTRACT FROM AUTHOR]

• A high-temperature CO 2 -responsive smart gel system is designed, and it has good heat and salt resistance. • The influence rules of CO 2 -responsive smart gel system properties are studied. • The viscosity-temperature chart of the smart gel is drawn. • Combined with statistical analysis methods, a mathematical model is constructed. • The order of influence degree of the studied factors on the gelation is obtained. The CO 2 capture, utilization and storage (CCUS) are very important. CO 2 -responsive materials have good CO 2 responsiveness and can play a certain role in CCUS. However, the use temperature of CO 2 -responsive surfactant is relatively low, and the main factors affecting their performance are still not clear, seriously affecting their large-scale application. In this work, a kind of high-temperature CO 2 -responsive surfactant was synthesized, and it can form a high-temperature CO 2 -responsive smart gel system when combined with counter ion salt. The effects of temperature, surfactant concentration, salinity, aging time and oil content on the properties of the CO 2 -responsive smart gel system were studied by means of rheological experiments and SEM characterization. Combined with statistical analysis methods, a large number of experimental data were analyzed and fitted, a mathematical model was constructed. The mathematical model was highly feasible and statistically significant. Based on the mathematical model, the main factors affecting the performance of the CO 2 -responsive smart gel system were analyzed, and the gelation mechanism of the gel system was obtained. This work is expected to provide some guidance for the future application of the CO 2 -responsive smart gel. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design of new gelator based on crystal engineering approach having urea functional group and thiazole moiety. • Seven gelators with varying aliphatic long chain were synthesized to realize delicate hydrophilic-hydrophobic balance. • Variable temperature SANS were used to understand the supramolecular packing of molecules in solid, liquid and gel phase. • Unprecedented high selectivity and sensitivity towards iodide ions was observed by urea containing gels. A simple series of thiazole-urea-aliphatic chain-based compounds (1–7) were designed and synthesized using the principle of Crystal Engineering. The aliphatic alkyl chain of compounds was varied to obtain the delicate hydrophobic-hydrophilic balance between solute–solvent molecules required to attain the supramolecular gelation. Interestingly, all the compounds turned out to be excellent gelators for polar solvents including water mixtures with alcohols and acetonitrile. To get an insight into the packing of molecules in solid-state, solution, and gel phases various physicochemical techniques were employed such as SANS, SEM, PXRD, DFT calculation, etc. UV–Vis spectrometric measurements of compound 1 in the solution phase were carried out to establish the anion sensing capability. Very high sensitivity and selectivity of iodide ion in presence of other ions and degelation of acetonitrile gel of compound 1 in presence of iodide salts, make these compounds a unique class of LMOGs. [ABSTRACT FROM AUTHOR]

The amidourea-based homoduplex was developed as a super organogelator, which could form stable gels in wide-tested solvents. And the reversible gel to solution transition was responsive to heat/cool and acid/base stimuli. The organogels were extensively investigated by H NMR, UV-visible absorption spectroscopy, fluorescence spectroscopy, scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Based on these data, the gelation mechanism was rationally proposed. The hydrogen-bonded homoduplexes served as the basic assembling units, and further aggregated into three dimensional networks via π-π stacking and van der Waals interactions, which consequently led to the entangled fibers for the gel formation. [ABSTRACT FROM AUTHOR]

Abstract: Using sodium caprylate as a model molecule, in the present work, we unraveled the gelation mechanism of sodium soaps in organic solvents from its correlation with the microstructure morphology. It is interesting to find that both the formation of organogels and radiation-like gel fibers are controlled by Na+ concentration in the system. As the gel-activator, the sodium ions not only accelerate the gelation process and enhance the gel networks, but also induce the morphology transformation from fibers to radiative nanoribbons. TEM and XRD characterization reveals that the Na+ enhanced effect should be ascribed to the structure transformation of sodium caprylate from layers to hexagonal packing, due to its reduced inter-separation after the addition of Na+. Based on these results, the gelation mechanism of sodium soaps has been also proposed. [Copyright &y& Elsevier]

The flow behavior, dynamic viscoelasticity, and optical rotation of aqueous solutions of wheat amylose were measured using a rheogoniometer and a polarimeter. The amylose solutions, at 25 °C, showed shear-thinning behavior at a concentration of 1.2%, but plastic behavior at 1.4 and 1.6%, the yield values of which were estimated to be 0.6 and 1.0 Pa, respectively. The viscosity of the wheat amylose increased a little with increase in temperature up to 10 or 20 °C at 1.2% or 1.4 and 1.6%, which was estimated to be a transition temperature. The elastic modulus increased with increase in concentration, and increased with increasing temperature up to 20, 25 and 30 °C, which was estimated to be a transition temperature, respectively, then decreased gradually but stayed at a large value even at high temperature (80 °C). A very low elastic modulus of the wheat amylose was observed upon addition of urea (4.0 M) and in alkaline solution (0.05 M NaOH) even at low temperature. The optical rotation of wheat amylose solution increased a little with decreasing temperature down to 25 °C, then increased rapidly with further decrease in the temperature. The mode of gelation mechanism of amylose molecules, which was previously proposed, was confirmed and a retrogradation mechanism of wheat amylose was proposed. [ABSTRACT FROM AUTHOR]

Salt ions play an important role in the quality structure of food and sensory properties. This study aims to investigate the effects of different concentrations of calcium chloride (0–0.012 mol/L) on the gel properties and interactions of heat-induced Mesona chinensis polysaccharide (MCP)-whey protein isolate (WPI) mixed gels. It was found that the apparent viscosity decreases gradually with the increase of calcium ion concentration, especially when the calcium ion concentration reaches 0.012 mol/L, the apparent viscosity is the lowest. The water holding capacity of the mixed gel decreased from 86.25% to 32.05% and the network structure of the gel became looser, which was consistent with low-field magnetometry results and the variation of microstructure. In the in vitro digestion experiments, the addition of 0.003 mol/L calcium chloride was effective in reducing the degradation of the gel. The results of chemical bonding analysis indicated that hydrogen bond and hydrophobic interactions were the key forces that promoting gel formation and maintaining the gels network structure. This study showed that calcium ions could change the contribution of hydrogen bonding, disulfide bonds, and hydrophobic interactions to the gelation process. [Display omitted] • The G′ and G″ values decreased with increasing calcium ion concentration. • High calcium ions concentration reduced water holding capacity. • The addition of 0.003 mol/L calcium ion reduced the degradation of the gel. • Hydrogen bonding and hydrophobic interactions are the main forces holding gels. [ABSTRACT FROM AUTHOR]

Abstract: In this work we present an analysis of the thermal behavior of hydroxypropylmethyl cellulose aqueous solutions, from room temperature to higher temperatures, above gelation. We focus on significant aspects, essentially overlooked in previous work, such as the correlation between polymer hydrophobicity and rheological behavior, and the shear effect on thermal gelation. Micropolarity and aggregation of the polymer chains were monitored by both UV/vis and fluorescence spectroscopic techniques, along with polarized light microscopy. Gel formation upon heating was investigated using rheological experiments, with both large strain (rotational) tests at different shear rates and small strain (oscillatory) tests. The present observations allow us to compose a picture of the evolution of the system upon heating: firstly, polymer reptation increases due to thermal motion, which leads to a weaker network. Secondly, above 55 °C, the polymer chains become more hydrophobic and polymer clusters start to form. Finally, the number of physical crosslinks between polymer clusters and the respective lifetimes increase and a three-dimensional network is formed. This network is drastically affected if higher shear rates, at non-Newtonian regimes, are applied to the system. [Copyright &y& Elsevier]

The kinetics of particle growth in lead zirconate titanate sol gel precursor solutions has been investigated. It was found that chemical reaction limited aggregation was responsible for most of the sol aging, followed by diffusion limited aggregation in the later stage. At the beginning, particles grow by reaction between initial polymers and particles. As the particle number-density increases, a particle-particle aggregation characterised by an exponential growth law becomes the predominant mechanism. When particles grow larger, towards gel formation, the aggregation changes to diffusion limited. Mathematical models derived according to the above mechanisms agreed well with experimentally measured particle growth profiles. [ABSTRACT FROM AUTHOR]

Continuous oscillatory experiments were used to investigate the viscoelastic properties and structural evolution of silica gels obtained from unsheared and presheared sols, at pH 8. The processes controlling structural evolution before, at and after the gel point are discussed. Although the viscoelastic properties of the aged gels are comparable (implying similar structures on length scales of several microns), their chemical properties and microstructures (<1 μm) are significantly different. This is directly related to the different aggregate structures formed in the unsheared and presheared systems (50 and 700 nm, respectively) and the associated concentration of surface hydroxyls available for cross-linking and formation of stable siloxane bonds. [ABSTRACT FROM AUTHOR]

Zirconium oxide gels were prepared by controlled hydrolysis and condensation of zirconium-n-propoxide in alcoholic solution. After completion of the gelation the aging and drying of the alcogel was observed in situ by Small and Wide Angle X-ray Scattering experiments at room temperature. The xerogels obtained have been annealed at different temperatures to crystallization. The structural changes were observed by using SAXS and WAXS. Structural models reproducing the experimental WAXS data have been simulated by the reverse Monte Carlo method. A comparison between zirconium oxide xerogels obtained under different thermal treatments was made and evidence was found that thermal treatment at higher temperatures and preparation conditions affect the atomic arrangement of these amorphous gels. [ABSTRACT FROM AUTHOR]

Silica aerogels are materials of very high porosity obtained through a sol-gel process. Since their structural properties greatly influence their acoustical and mechanical properties, it is important to follow how the different chemical reactions occur during this process. We present a study of these evolutions for two different types of alcogels through acoustical measurements in the ultrasonic range. These samples have been chosen because of the significantly different behavior of the derived aerogels. The data obtained during gelation show fluctuations of the velocity that can be interpreted in terms of chemical changes. The absence of major changes in the velocity before and after gelation is explained with the aid of Biot's theory of acoustic propagation in porous media. [ABSTRACT FROM AUTHOR]

We investigated the influence of formamide on the acid-catalyzed sol-gel process at 40°C, by Fourier transformed infrared spectroscopy. Two silica sols were studied: one containing formamide and one without. Following the time evolution of both the Si−O(H) stretching vibration at around 950 cm−1 and the Si−O(−Si) vibration between 1080 and 1200 cm−1, we were able to describe the structural evolution of each sol. We thus observed, in the case of the formamide containing sol, a peculiar two-step structural evolution which eventually resulted in a highly interconnected gel. [ABSTRACT FROM AUTHOR]

As shown in the figure, viscosity modulus dominates in polymer solution. However, the elastic modulus of acid gel fracturing fluid is always greater than the viscous modulus, showing obvious gel characteristics. SEM showed that the fracture fluid had obvious structural changes before and after cross-linking. In petroleum exploitation, fracturing is a very important technique for the reservoir with low porosity and permeability. The fracturing fluid is the key to fracturing operation. Due to the limitation of lithology complexity, it is difficult for conventional acid-based fracturing fluids to meet technical requirements during the production of carbonate oil and gas resources. In this work, a novel acid gel fracturing fluid was designed. The system has high viscosity which is convenient to carry proppant. Meanwhile, the fluid has good basic properties to meet on-site operation requirements. Since the properties of fracturing fluid depend not only on the molecular structure of thickener, but also on the crosslinked structure formed by polymer and crosslinker. The dynamic cross-linking mechanism of this acid gel fracturing fluid system was focused on. The differences in fluid properties between polymer based fluid and fracturing fluid were investigated by conducting viscoelastic tests. A rheological dynamic model based on the change of viscosity with reaction time was established. The effect of shear rate on cross-linking viscosity and reaction rate was studied. Moreover, the microstructure changes of the system before and after the gelation reaction were revealed through the scanning electron microscopy (SEM) experiment. Based on these experimental results, the cross-linking mechanism of this novel acid gel fracturing fluid can be concluded, which benefits the application in oilfield. [ABSTRACT FROM AUTHOR]

Silk fibroin hydrogel not only has biocompatibility, but also has environmental response ability. It plays an important role in the development of material. The gelation mechanism of silk fibroin hydrogel is very important to textile and medicine fields. The molecular dynamics simulation was used to discuss the structure and non-bond interaction of silk fibroin hydrogel. The results show that the non-bond interactions between silk fibroin molecules and water molecules have certain influence on the formation of silk fibroin hydrogel. According to the hydrogen bond analysis, the hydrogen bonds are mainly formed between random coil peptide fragments at the two ends of silk fibroin molecules and residues 252-254 are the key residues. The electrostatic and polar solvation interactions between silk fibroin molecules plays a major role in cross-linking of the coil segments of two silk fibroin molecules.