Rate Of Gel Formation Research Articles

Experimental Evaluation of Performance of a Low-Initial-Viscosity Gel Flooding System.

In order to effectively adjust reservoir heterogeneity and further exploit the remaining oil, a new type of low-viscosity gel was prepared by adding a regulating agent, retarder, and reinforcing agent on the basis of a polymer + Cr3+ crosslinking system. The new gel has the advantages of low initial viscosity, a slow gel formation rate, and high strength after gel formation. The effectiveness of the gel was verified through three-layer core displacement experiments, and the injection scheme was optimized by changing the slug combination of the polymer and the gel. The results showed that the gel can effectively block the high-permeability layer and adjust reservoir heterogeneity. An injection of 0.1 pore volume (PV) low-initial-viscosity gel can improve oil recovery by 5.10%. By changing the slug combination of the gel and polymer, oil recovery was further increased by 3.12% when using an injection of 0.07 PV low-initial-viscosity gel +0.2 PV high-concentration polymer +0.05 PV low-initial-viscosity gel +0.5 PV high-concentration polymer.

Effect and mechanism of freezing on the quality and structure of soymilk gel induced by different salt ions.

The increasing attention toward frozen soy-based foods has sparked interest. Variations exist in the quality and structure of soymilk gels induced by different salt ions, leading to diverse changes post-freezing. This study compared and analyzed the effects of calcium chloride (CC), magnesium chloride (MC) and calcium sulfate (CS) on the quality characteristics and protein structure changes of soymilk gels (CC-S, MC-S and CS-S) before and after freezing, and clarified the mechanisms of freezing on soymilk gel. The formation rate of soymilk gel is influenced by the type of salt ions. In comparison to CS and MC, soymilk gel induced by CC exhibited the fastest formation rate, highest gel hardness, lowest moisture content, and smaller gel pores. However, freezing treatment deteriorated the quality of soymilk gel induced by different salt ions, leading to a decline in textural properties (hardness and chewiness). Among these, the textual state of CC-induced soymilk gel remained optimal, exhibiting the least apparent damage and minimal cooking loss. Freezing treatments prompt a transition of soymilk gel secondary structure from β-turns to β-sheets, disrupting the protein's tertiary structure. Furthermore, freezing treatments also fostered the crosslinking between soymilk gel protein, increasing the content of disulfide bonds. The quality of frozen soymilk gel is influenced by the rate of gel formation induced by salt ions. After freezing, soymilk gel with faster gelation rates exhibited a greater tendency for the transformation of protein-water interactions into protein-protein interactions. They showed a higher degree of disulfide bond formation, resulting in a more tightly knit and firm frozen gel network structure with denser and more uniformly distributed pores. © 2024 Society of Chemical Industry.

One Step Encapsulation of Mesenchymal Stromal Cells in PEG Norbornene Microgels for Therapeutic Actions.

Cell therapies require control over the cellular response under standardized conditions to ensure continuous delivery of therapeutic agents. Cell encapsulation in biomaterials can be particularly effective at providing cells with a uniformly supportive and permissive cell microenvironment. In this study, two microfluidic droplet device designs were used to successfully encapsulate equine mesenchymal stromal cells (MSCs) into photopolymerized polyethylene glycol norbornene (PEGNB) microscale (∼100-200 μm) hydrogel particles (microgels) in a single on-chip step. To overcome the slow cross-linking kinetics of thiol-ene reactions, long dithiol linkers were used in combination with a polymerization chamber customized to achieve precise retention time for microgels while maintaining cytocompatibility. Thus, homogeneous cell-laden microgels could be continuously fabricated in a high-throughput fashion. Varying linker length mediated both the gel formation rate and material physical properties (stiffness, mass transport, and mesh size) of fabricated microgels. Postencapsulation cell viability and therapeutic indicators of MSCs were evaluated over 14 days, during which the viability remained at least 90%. Gene expression of selected cytokines was not adversely affected by microencapsulation compared to monolayer MSCs. Notably, PEGNB-3.5k microgels rendered significant elevation in FGF-2 and TGF-β on the transcription level, and conditioned media collected from these cultures showed robust promotion in the migration and proliferation of fibroblasts. Collectively, standardized MSC on-chip encapsulation will lead to informed and precise translation to clinical studies, ultimately advancing a variety of tissue engineering and regenerative medicine practices.

The mechanism of alkali-induced rice protein gel formation: Effect of alkali concentration and temperature

Rice protein (RP) is a high-quality hypoallergenic plant protein, but its extremely poor water solubility makes it difficult to be applied in liquid food systems. Therefore, in-depth exploration of its gel properties is an effective way to broaden the application scenarios of RP. In this work, it was first found that the rate and strength of gel formation by RP at 25 °C strongly depended on the increase in alkali concentration (from 0.05 M to 0.125 M), i.e., alkali concentrations above 0.075 M were sufficient to induce the formation of a stable gel by 10% (w/v) of RP in 0.5 h. Increasing the temperature during alkali-induced RP gel formation (50 °C, 80 °C) greatly increased the rate of gel formation, whereas prolonged (>30 min) heat treatment resulted in liquefaction of the gel. A more in-depth analysis revealed that the alkali was able to depolymerize glutelin within the agglomerates in its native state, thereby forming a gel network among glutelin molecules at lower alkali concentrations (CNaOH = 0.075 M) mainly through hydrophobic interactions. Whereas, higher alkali concentration (CNaOH = 0.125 M) resulted in the rapid transformation of exposed free sulfhydryl groups into disulfide bonds, thus exerting a major contribution to the gel network, followed by hydrogen bonding. Furthermore, the phenomenon of heat-induced gel liquefaction was mainly attributed to the dissociation of glutelin subunits and was accompanied by an increase in the disordered structure of proteins in the amide III region. These findings may provide a scientific basis for the development of rice protein gel foods.

Biomediated control of colloidal silica grouting using microbial fermentation

Colloidal silica grouting is a ground improvement technique capable of stabilizing weak problematic soils and achieving large reductions in soil hydraulic conductivities for applications including earthquake-induced liquefaction mitigation and groundwater flow control. In the conventional approach, chemical accelerants are added to colloidal silica suspensions that are introduced into soils targeted for improvement and the formation of a semi-solid silica gel occurs over time at a rate controlled by suspension chemistry and in situ geochemical conditions. Although the process has been extensively investigated, controlling the rate of gel formation in the presence of varying subsurface conditions and the limited ability of conventional methods to effectively monitor the gel formation process has posed practical challenges. In this study, a biomediated soil improvement process is proposed which utilizes enriched fermentative microorganisms to control the gelation of colloidal silica grouts through solution pH reductions and ionic strength increases. Four series of batch experiments were performed to investigate the ability of glucose fermenting microorganisms to be enriched in natural sands to induce geochemical changes capable of mediating silica gel formation and assess the effect of treatment solution composition on pH reduction behaviors. Complementary batch and soil column experiments were subsequently performed to upscale the process and explore the effectiveness of chemical, hydraulic, and geophysical methods to monitor microbial activity, gel formation, and engineering improvements. Results demonstrate that fermentative microorganisms can be successfully enriched and mediate gel formation in suspensions that would otherwise remain highly stable, thereby forgoing the need for chemical accelerants, increasing the reliability and control of colloidal silica grouting, enabling new monitoring approaches, and affording engineering enhancements comparable to conventional colloidal silica grouts.

Interactions involved in heat-induced gelatin gel containing hsian-tsao gum, and mechanisms to improve its properties.

Hsian-tsao gum (HG) has unique gel-promoting and nutritional properties; however, its use in processed foods is limited to starchy foods, partially due to a lack of knowledge related to its interaction with proteins. This study elucidated the interaction mechanism of heat-induced gelatin (G) (50 g kg-1 ) gel fortified with HG (0 ~ 20 g kg-1 ) using rheology, Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), large deformation tests, low-field nuclear magnetic resonance (LF-NMR), and confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM). Heating promoted synergistic interactions between G and more HG molecules with enhanced apparent viscosity and higher storage modulus G' than loss modulus G″, thus shortening the gel time (tg ) of G-HG sols into gels. Fourier-transform infrared spectroscopy and DSC also confirmed the chemical interactions that occurred, facilitating the formation of β-sheet structures of G. The microstructure of G gradually formed separate, coarse strands, and aggregated as HG was added, as observed by CLSM and SEM. This accelerated the gel formation rate and changed the textural properties. Although HG caused a disruptive decrease in the helix structure of G, it was possible to compensate for this by accelerating synergistic interactions, including depletion attractions and Maillard reactions, by heating. Hsian-tsao gum interacted synergistically with G as a result of heating and this accelerated the gel formation rate and improved the gel properties. Novel complex gels could be designed by blending HG to improve the gel properties of G in the heat processing of the food gel formulation. © 2022 Society of Chemical Industry.

Lime Peel Oil-Incorporated Rosin-Based Antimicrobial In Situ Forming Gel.

Localized intra-periodontal pocket drug delivery using an injectable in situ forming gel is an effective periodontitis treatment. The aqueous insoluble property of rosin is suitable for preparing a solvent exchange-induced in situ forming gel. This study aims to investigate the role of incorporating lime peel oil (LO) on the physicochemical properties of injectable in situ forming gels based on rosin loaded with 5% w/w doxycycline hyclate (DH) in dimethyl sulfoxide (DMSO) and N-methyl pyrrolidone (NMP). Their gel formation, viscosity, injectability, mechanical properties, wettability, drug release, and antimicrobial activities were evaluated. The presence of LO slowed gel formation due to the loose precipitate formation of gel with a high LO content. The viscosity and injectability were slightly increased with higher LO content for the DH-loaded rosin-based in situ forming gel. The addition of 10% LO lowered gel hardness with higher adhesion. LO incorporation promoted a higher drug release pattern than the no oil-added formulation over 10 days and the gel formation rate related to burst drug release. The drug release kinetics followed the non-Fickian diffusion mechanism for oil-added formulations. LO exhibited high antimicrobial activity against Porphyromonas gingivalis and Staphylococcus aureus. The DH-loaded rosin in situ forming gel with an addition of LO (0, 2.5, 5, and 10% w/w) inhibited all tested microorganisms. Adding 10% LO to rosin-based in situ forming gel improved the antimicrobial activities, especially for the P. gingivalis and S. aureus. As a result, the study demonstrates the possibility of using an LO amount of less than 10% loading into a rosin-based in situ forming gel for efficient periodontitis treatment.

GENERATION OF SYNTHETICAL MEDICAL DATA BY MDR-ANALYSIS

Purpose: The purpose of this article is to determine the dependence of the rate of gel formation on the type of reagent-inhibitor of the gel formation process, and to study the kinetic dependences of gel formation of silicate compositions in the presence of compounds that regulate the rate of gel formation. Research methods: Direct and reverse titration, potentiometric titration, pH-metry, determination of the dynamic viscosity on a rotational viscometer, axial compression method to determine the elastic modulus were used to study the possibility of using chemical reagents as gelation inhibitors. Results: The possibility of using inorganic and organic additives to slow down the gel formation process and the effect of these additives on the strength of the gel, their thermodynamic parameters have been researched. Discussion: The adding of organic acids into the silicate composition as "crosslinking agents" slows down the gel formation process, while replacing hydrochloric acid with other gel acids that slow down the gel formation process does not lead to a decrease in the strength characteristics of these systems compared to the standard. It was found that with an increase in the gelation time, the strength of the gels decreases, and the syneresis increases; the adding of inhibitor additives insignificantly worsens the filterability of silicate compositions, which in general have bad filterability, leading to an increase in resistance during filtration at the inlet section of the sample. Observations have shown that the addition of additives-inhibitors does not affect the thermal stability of gels, regardless of the additives' nature.

Validation of the relationship between coagulopathy and localization of hydroxyethyl starch on the vascular endothelium in a rat hemodilution model

Various anticoagulant properties have been associated with hydroxyethyl starch (HES). However, the mechanism remains unclear and it has not been fully considered whether these properties are beyond the dilutional effect itself. The aim of this study was to reproduce the coagulopathy induced by HES and to test the hypothesis that the coagulopathy is caused by endothelial or glycocalyx damage due to localization of HES on the endothelium, which is caused by the high shear viscosity of dilutional blood. Using a rat model, we compared blood coagulability measured by Sonoclot, levels of endothelial and glycocalyx damage markers and coagulation factors, and blood shear viscosity when hemodilution was performed with physiological saline (PS), 6% HES 130/0.4 in PS, and 10% HES 200/0.5 in PS. We also evaluated the localization rates of fluorescently labeled HES on endothelium in the isolated aorta. HES decreased the fibrin gel formation rate more than did PS. HES was shown to cover the endothelium, possibly due to its high shear viscosity, and this mechanism potentially acted to protect, rather than damage, the endothelium and glycocalyx. However, this covering effect may be the cause of coagulopathy due to inhibition of von Willebrand factor secretion from the endothelium.

Evolution of structure and dynamics of thermo-reversible nanoparticle gels-A combined XPCS and rheology study.

A combined X-ray photon correlation spectroscopy and rheology study is carried out to capture the evolution of structure, fast particle-scale dynamics, and moduli (elastic and loss) at early times of gel formation near the fluid-gel boundary of a suspension of nanoparticles. The system is comprised of moderately concentrated suspensions of octadecyl silica in decalin (ϕ = 0.2) undergoing thermoreversible gelation. Near the gel boundary, the rate of gel formation is very sensitive to changes in attraction strength. However, we find that at different attraction strengths, the system goes through identical intermediate states of microscopic and macroscopic behavior, even though the absolute time needed to form a gel varies by orders of magnitude. We identify a single dimensionless time parameter, tw/tg, where tw is the wait time following the quench and tg is the rheologically determined gel time, that captures the similarity in gel formation at a range of attraction strengths. Following a temperature quench below the gel boundary, the system is initially fluidlike and forms diffusive clusters (∼8.5 times the particle diameter). After a lag-time, tL, clusters aggregate to form a network like structure which is characterized by the onset of mechanical rigidity and a rapid growth in microscopic relaxation times. At tg, the Baxter parameter obtained from adhesive hard sphere fits of the structure factor attains a constant value corresponding to the theoretical percolation boundary, thus demonstrating that gelation is percolation driven.

Effects of microwave heating on the gelation properties of heat-induced Alaska Pollock ( Theragra chalcogramma) surimi.

In the present study, we examined the properties of Alaska Pollock ( Theragra chalcogramma) surimi gels in response microwave heating at different powers (300, 400, or 500 W) and time (10, 20, or 30 min). The surimi gels heated by a microwave at 300 W for 10 min showed the highest gel strength and water-holding capacity. Increasing the power and time resulted in decreases in both the gel strength and water-holding capacity. The gel formation rate of microwave-heated gels was significantly higher than that produced by water bath heating. In addition, differential scanning calorimetry indicated that microwave heating caused less damage to the native structures of myosin and actin than water bath heating. Microstructure studies revealed that microwave heating contributed to the formation of a denser and stronger frame of the surimi gels. Raman spectroscopy indicated that the degree of the secondary structure denaturation caused by microwave heating was less than that induced by water bath heating. Thus, the results demonstrated that microwave heating is a promising method to enhance the gelation properties of surimi.

Drying Kinetics and Optimisation of Pectin Extraction from Banana Peels via Response Surface Methodology

Banana peels which are the waste in abundance, are used to extract valuable pectin. The gelling ability of the pectin has gained attention in food and pharmaceutical industries. This research aims to select the best drying kinetic model for banana peels and also optimize the pectin extraction process using Box-Behnken response surface design (BBD). Determination of pectin gelling mechanism using degree of esterification (DE) is also focused in this research. In this study, oven drying with temperature 50°C was chosen as the best drying temperature due to highest extraction yield. Furthermore, Page-Two-term model was selected as the best model to describe the drying kinetics of banana peels due to highest R2 value (0.9991) and lowest RMSE value (0.001). The optimal extraction conditions given by BBD were 75°C extraction temperature, 23 min extraction time and 1:33.3 g/ml solid-liquid ratio. Likewise, the DE for both pectins extracted using unoptimised and optimised conditions were 71.92±1.38% and 76.1±2.07% respectively. Both of the pectins were classified as high-methoxyl pectins. The pectin with higher DE also indicated that the rate of gel formation is higher. The results showed that the pectin yield and gelling time has successfully improved after optimised the pectin extraction process.

A multiscale investigation of reaction kinetics, phase formation, and mechanical properties of metakaolin geopolymers

A multiscale study is presented of the reaction kinetics, phase formation, mechanical properties of metakaolin-based geopolymers by varying Si/Al ratios of 1.2–2.2 and Na/Al ratios of 0.6–1.2. Macro- and nano-mechanical properties of geopolymer samples were determined by unconfined compression testing and grid nanoindentation technique, respectively. The latter, in combination with statistical deconvolution, also enables the extraction of generally 4 distinct phases together with their nanomechanical properties and volumetric fraction within the synthesized geopolymers. Moreover, the reaction kinetics, phase formation (particularly geopolymer gel development), and mechanical property development were investigated by characterizing geopolymers cured at the final setting time, 7, and 28 days. Phase formation was characterized by Fourier transform infrared spectroscopy (FTIR) via monitoring the evolution of the Si-O-T (T: Si or Al) and Al-O bonds. Results illustrate that the fraction of geopolymer gels dominantly governs the mechanical behavior, both of which increase with the Si/Al and Na/Al molar ratios, while the final setting time increases with the Si/Al ratio, but decreases with the Na/Al ratio. The chemical composition for the best mechanical performance of the studied geopolymers is a Si/Al ratio of 1.7 and Na/Al ratio of 0.9. The relationships among geopolymer chemical compositions, geopolymer gel formation rate, and macromechanical properties are also discussed.

Biochemical and rheological characterization of a protease from fruits of Withania coagulans with a milk-clotting activity

A protease from Withania coagulans fruits was evaluated for milk-clotting properties. The optimum temperature and pH for enzyme activity were 70°C and 4, respectively. The protease also exhibited an excellent thermal stability at 60°C for 30 min. Fractional precipitation using ammonium sulfate showed that the 40–50% fraction (F5) possessed the highest milk-clotting activity. The F5 fraction showed a Mw band of 66 kDa by SDS-PAGE. Gel formation was monitored using low amplitude oscillatory rheology at different temperatures. An Arrhenius plot was used to describe the temperature dependence of the gelation rate parameter. Time sweep testing showed that an increase in temperature was accompanied by a decrease in the gelation onset time, a higher gel formation rate, and higher values for final gel strength. W.coagulans fruits have potential for use as a rennet substitute.

Structure and formation processes of syndiotactic-polystyrene or styrene-based copolymer-organic solvent gels studied using scanning microscopic light scattering

The network structure of syndiotactic-polystyrene (sPS)- or syndiotactic-poly(styrene-co-4-R-styrene)-organic solvent gels has been quantitatively studied by means of scanning microscopic light scattering (SMILS). SMILS analysis indicated that sPS gels prepared in chloroform, benzene, toluene, and o-dichlorobenzene (ODCB) formed network structures with small mesh sizes, ~0.6–1.8 nm, and large cluster structures, ~1000–6000 nm. The cluster size in the gels increased with increasing sPS concentration. The mesh and cluster sizes of sPS gels prepared in ODCB was the smallest among the used solvents owing to its high viscosity. Gelation of the St/CH3St (MeSt)-toluene system at high temperatures induced slow gel formation and made it possible to trace the time evolution of the network structure by SMILS. tert-C4H9St (BuSt) units in St/BuSt drastically decreased the gel formation rate, and the formation process of the St/BuSt-toluene system could be traced by SMILS and FT-IR spectroscopy at room temperature. The results indicated growth of the cluster structure during gelation. St/4-hydroxystyrene formed gels in dioxane. A gel of an St copolymer containing an anthracene (An) group was prepared in toluene, and photodimerization of the An groups was induced by UV irradiation accompanied by formation of the large cluster structure. Network structure of syndiotactic-polystyrene (sPS) or syndiotactic-poly(styrene-co-4-R-styrene) (St/RSt) -organic solvents gels has been quantitatively studied by means of a scanning microscopic light scattering (SMILS). The SMILS analysis cleared that most of the gels showed relaxation peaks derived from small mesh size ~0.6–1.8 nm and large cluster structure ~1000–6000 nm, and a gel formation model was proposed based on the analysis. Interaction between R groups (R=OH, antracenecarbonyl) affected the network structure of the gels.

Effect of shear on physicochemical properties of matrix metalloproteinase responsive silk-elastinlike hydrogels

Silk-elastinlike protein polymers (SELPs) have been fabricated as matrices for controlled delivery of bioactive agents. In this application the need for an environmentally responsive, degradable polymer has risen to improve treatment outcomes. To satisfy this need, we have designed, synthesized, and expressed SELPs with matrix metalloproteinase (MMP) degradable sequences inserted in distinct regions of the polymer backbone. Upon characterization of the physicochemical properties of newly synthesized analogs, it was determined that conditioning of the polymers was necessary for normalization of batch properties, and to generate a more robust polymer network suitable for delivery. In this report we have examined the use of shear stress to condition synthesized material prior to application as a controlled release matrix. The application of high shear to SELPs results in significant changes in physiochemical properties as assayed by swelling ratio, soluble fraction release, rate of gel formation, stiffness of hydrogels, and nanoparticle release from matrices. These observed changes in material characteristics may be caused by the removal of semi-stable secondary and tertiary structures from single polymer strands leading to a more robust hydrogel with greater intermolecular interaction.

Controlled release of doxorubicin and Smac‐derived pro‐apoptotic peptide from self‐assembled KLD‐based peptide hydrogels

Self‐assembled peptide hydrogels comprise an important class of biomaterials that find application in tissue engineering and drug delivery. We have developed injectable in situ‐forming hydrogel formulations based on self‐assembled KLD motifs to control the delivery of a conventional cytotoxic drug (doxorubicin [DOX]) or a Smac‐derived pro‐apoptotic peptide (SDPP) for cancer therapy. The core KLD peptide ([KLDL]3) was separated into two β‐sheet peptides by a three or four glycine‐containing spacer (designated as 3G or 4G, respectively) or by a spacer containing four glycines and a phenylalanine (termed 4GF) to fine tune and influence the bulk properties. We found that the KLD‐based hydrogel can effectively load DOX and SDPP within the hydrogel network. Addition of a three or four glycine‐containing spacer arm decreased the time for gel formation, while inclusion of a single aromatic amino acid (F) into 4G sequence (4GF) significantly increased the rate of gel formation and improved its mechanical strength when compared to 3G‐ and 4G‐containing gels. KLD16‐ and 4GF‐based hydrogels presenting higher peptide concentrations can self‐assemble very rapidly (in a few seconds) and were very effective at controlling the release of DOX and SDPP and inhibiting tumor cell growth in vitro. Pre‐complexation of SDPP with polyanionic molecule (polyglutamic acid) further sustained in vitro drug release from 4GF‐based formulations. This study is the first to test interactions between KLD‐based hydrogel matrices and DOX or SDPP for local drug delivery applications. Copyright © 2014 John Wiley & Sons, Ltd.

Structure–thermomechanical property correlation of moisture cured poly(urethane-urea)/clay nanocomposite coatings

A series of poly(urethane-urea)/clay nanocomposite coatings were prepared by moisture curing of isophorone diisocyanate (IPDI) capped hydroxyl terminated polybutadiene (HTPB)/clay dispersions in a relative humidity (RH) of 50% at 25°C. The curing progress was studied by periodic measurement of gel fraction of the coating samples. The studies revealed tortuosity effects of clay toward moisture diffusion, thus delaying the induction period of gelation, time for complete cure and rate of gel formation of the nanocomposite coatings. The clay platelets were found to be intercalated in the poly(urethane-urea) matrix, evidenced from wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Effects of nanoclay on state of the hard and soft segments were investigated by WAXD, differential scanning calorimetry (DSC), temperature modulated DSC (MDSC) and solid-state nuclear magnetic resonance spectroscopy (NMR). WAXD studies revealed unusually ordered hard segment morphology of the moisture cured poly(urethane-urea) and its nanocomposites. Slower soft segment dynamics upon clay addition was evident from concentration dependant broadening of the line widths of the NMR peaks, and decreasing reversible heat capacity changes at soft segment glass transition. The volume fraction of immobilized soft segments of the nanocomposites was determined from MDSC and was found to increase linearly with clay loading. The mechanical property analysis showed simultaneous reinforcement and toughening effect of nanoclay on the MCPU matrix. The increment in mechanical property of the nanocomposites varied proportionately with the volume fraction of immobilized soft segments.

Investigation of the Mechanism of Temperature-Responsiveness of Metal-Cholate Supramolecular Hydrogels

Temperature-promoted hydrogel formation was investigated in a mixed solution of sodium cholate and metal ions. Transmission electron microscopy (TEM) was used to characterize the morphology of the microstructures of the hydrogels, and nanofibers were observed. The arrangement of the cholate and metal ions was proposed according to the X-ray diffraction (XRD) measurements. Rheological measurements revealed that the strength of the hydrogels increases with increasing temperature, while the fluorescence of the gels increased as well. Increasing the temperature also increased the gel formation rate. The critical micelle concentration of sodium cholate solution decreased slightly with increasing temperature. On the basis of the experimental results, we propose that the increased hydrophobicity of cholate ions with increasing temperature leads to stronger hydrogen bonding between cholate ions, which accounts for the unique heating-enhanced gelation behavior.

Effects of additives and solvents on the gel formation rate and on the texture of P- and Si-doped TiO 2 materials

Organic/inorganic hybrid TiO 2 xerogels have been synthesized from titanium tetraisopropoxide and an organosilylated or organophosphorylated additive either in 2-methoxyethanol or isopropanol. The mechanisms of formation of the gels have been studied before gelation by liquid NMR spectroscopy and connected to their structure after drying analyzed by Raman spectroscopy, solid state NMR and N 2 adsorption/desorption. The effects of the additives and solvents on the gel formation rate and on the texture of the xerogel have been addressed.