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On heating, egg white proteins unfold, aggregate through intermolecular interactions of non-covalent and covalent bonds, and form networks to gel. Since the physical properties of egg white gel have a great influence on the texture of foods that use egg white, the control techniques and mechanisms have been extensively studied. In addition to conventionally known hydrophobic interactions and disulfide bonds, lanthionine and lysinoalanine bonds are deeply involved in the heat gelation of egg white. Recently, it was revealed that the covalent bonds are also involved in the formation of soluble aggregates on dry heat treatment of dried egg white. Controlling the formation of soluble egg white protein aggregates is considered a key factor in controlling the heat-induced gelation of egg whites. The aggregation and gelation properties have been studied using various methods, such as the Maillard reaction and electrochemical reaction. [ABSTRACT FROM AUTHOR]

Unidirectional anisotropic pore morphologies could be created by using a gelation of mullite particles dispersed slurry with and without an anti-freezing protein additive, and the freezing process, resulting in micrometer-sized cells with very high porosities of up to 91 vol%. The addition of ice binding proteins effectively inhibited the formation of coarse ice crystals, reduced the resultant cell size and provided uniform size distribution in insulators obtained. The insulators prepared showed the thermal conductivity from 0.23 to 0.38 W/mK and the compressive strength around 1.4–21.7 MPa. These properties could be modulated by varying process parameters of the gelation and freezing with solid loading in the initial slurry, anti-freezing protein, sintering additive. This unique approach can be used to produce insulators with macro-cellular anisotropic morphology and very high porosity, suitable for a variety of industrial applications. [ABSTRACT FROM AUTHOR]

Penetrating flows of an aqueous solution of sodium salicylate (NaSal) through an aqueous solution of cetyltrimethylammonium bromide (CTAB) in a circular tube were investigated experimentally. The NaSal solution flowed through the CTAB solution while displacing it. Network structures of wormlike micelles are formed on the interface between the solutions, and gelation occurs there. Although each test fluid has a similar Newtonian viscosity, CTAB/NaSal mixtures had strong viscoelasticity, and their viscosity greatly increased because of the gelation. Consequently, several flow patterns that do not appear in the case of Newtonian/Newtonian penetrating flows were observed. The flow patterns of the core of the penetrating flow were classified into five patterns and were mapped onto a plane of the molar concentration ratio S of NaSal to CTAB and the penetration velocity U. The core exhibited a saw-tooth pattern at small U, which changed to a corkscrew pattern or an elastic recoil pattern as U increased. Elastic recoil patterns appeared at S = 3.0 and 5.0, where the relaxation time of a CTAB/NaSal solution is relatively long. Furthermore, a novel flow pattern in which the core flow exhibits repeated elastic recoiling was observed. In this pattern, the contracting part of the core flow exhibited alternate stretching and recoiling. Moreover, a unique phenomenon of a penetrating flow with gelation was observed. In this phenomenon, a stable tip was newly formed by the gelation after the breakup of a core. The displacement rate decreases with increasing penetration velocity and tends to be small when unstable flow patterns appear.

For the purpose of drug-carrying in oral administration, pH-responsive polyvinyl alcohol (PVA) hydrogels were prepared by the gelation of PVA with tetmcarboxylic acid dianhydride as crosslinking part and pH-sensitive part. The resulting hydrogels were estimated on the swelling behavior and the releasing behavior of loaded drug in pH 1.6 buffer solution as imitation of gastric condition and pH 7.4 buffer solution as imitation of intestinal condition at 37°C. The swelling degree was drastically decreased in pH 1.6 buffer solution, but high swelling degree was observed in pH 7.4 buffer solution at 37°C. The equilibrium swelling degree in pH 7.4 buffer solution at 37°C was dependent on the amount of carboxylic acid groups introduced in hydrogels. The releasing behavior of diclofenac sodium (DFNa) as acidic model drug was analogous to the swelling behavior of hydrogels. The releasing rate of DFNa was also dependent on the amount of carboxylic acid groups introduced in hydrogels. However, the release of imipramine hydrochloride as basic model drug was not controlled with pH. [ABSTRACT FROM AUTHOR]

Alginate micro-gel (AMG) containing a model compound, hydrocortisone (HC), was prepared by high pressure water method. The release profile of HC from AMG was then investigated. The mean particle size of AMG was less than 100pro: the size was controllable by the pressure of water. HC incorporated in AMG was immediately dissolved in physiological saline; the dissolution profile was reproducible. These results suggest that AMG is potentially useful to improve the solubility of water-insoluble compounds. [ABSTRACT FROM AUTHOR]

The polarity environment of ovalbumin (OVA) surface was evaluated by the ESR measurement of spin-labeled OVA (labeled OVA). The anisotropic g and hyperfine splitting tensors A of the labeled OVA were estimated. The result clarified that the surface of labeled OVA changed into a hydrophobic environment due to the heat-denaturation. From the evaluation of molecular mobility by using the ESR spectra of labeled OVA, it has become apparent that the molecular mobility of OVA was suppressed by the gelation (heat-denaturation). When the gel structures were characterized, it was difficult to verify a working hypothesis directly until now. However, the microscopic change resulting from the gelation was able to be investigated simply and un-destructively by the ESR measurements of labeled OVA. [ABSTRACT FROM AUTHOR]

Young's modulus measurements and junction length estimates have been performed on poly(vinyl alcohol) (PVA) sample in mixtures of dimethyl sulfoxide (DMSO) and water with various mixing ratios to investigate the relationship between gel structure and mechanical strength. The interaction parameter between PVA and DMSO/water mixed solvent was also estimated from swelling experiments. The junction length ζ in number of vinyl alcohol units was estimated with the aid of the Tanaka and Stockmayer theory (TS theory), which is based upon the conjecture that junction points of a gel are aggregates comprised of ζ units in length and S sequences in cross section. The Young's modulus value of PVA gel increased with an increase in the DMSO volume fraction up to about 60 vol% and the further increased fractions led to a decrease in Young's modulus. Both χ12 and ζ were also dependent on the DMSO volume fraction, similar to Young's modulus. These results indicate that gelation of PVA in a poorer solvent provided the longer junction lengths, resulting in the PVA gel formation with high mechanical strength. [ABSTRACT FROM AUTHOR]

Ionic liquids are very attractive recent materials as electrolytes in electrochemistry. By using gelators derived from a cyclic dipeptide, it is possible to gelate ionic liquids. The self-diffusion coefficient of ionic species in the ionic liquid gel were measured using the PFGSE NMR method. The higher ionic conductivity of ionic gel can be explained by the higher self-diffusion coefficient of ionic species comparaed to other types of gels. In addition, we estimated the pore size of the gel structure based on the diffusion coefficient data. [ABSTRACT FROM AUTHOR]

In syndiotactic polystyrene (sPS), the stereoisomeric configurations around the main chain sites alternate regularly. This polymer is known to form a thermoreversible physical gel in moderately concentrated solutions. In this study, the gelation process of sPS solution was investigated through measurement of in Situ Fourier transform infrared (FT IR) spectra, Moreover, the junction size S and the Young's modulus E of sPS gel was estimated as a function of solvent power, i.e., the degree of swelling at equilibrium, qmax. The time-resolved FT IR spectra suggested that sPS random coil chains in a relatively poor solvent such as toluene having the small value of qmax turn quickly into the T2G2 conformation, followed by gelation. On the other hand, the T2G2 conformation appears very slowly in a relatively good solvent such as chloroform having the large qmax value. The junction size S as well as Young's modulus E became larger with decreasing qmax. [ABSTRACT FROM AUTHOR]

Gelation behaviors of poly (vinyl alcohol) /sodium polyalginate (PVA/ALG) aqueous solutions with low ALG content (PVA: 21 g/dL; ALG: 0.55 g/dL) were examined by dynamic mechanical analysis and small angle neutron scattering (SANS). The gelation process does not depend on the order of the gelation of components; SANS intensities at small wave vectors q as well as at high q are almost equal to the sum of the values for the components. Young's moduli E and EPVA for PVA/ALG gel films immersed in CaCl2 solutions and PVA film immersed in water, respectively, were obtained by simple elongation measurements. The increment of modulus ΔE=E-EPVA, was proportional to the CaCl2 concentration. From these results, we concluded that PVA/ALG systems with low ALG content compose an interpenetrating network and that the final structure does not depend on the gelation order of components. [ABSTRACT FROM AUTHOR]