Gel-like phases

The structure of these gel-like systems of micelles is very different from that of conventional electrophoresis media made from chemically and physically cross-linked polymers of polyacrylamide and agarose [75], The absence of chemical or physical cross-links in the Pluronic gel-like phases may allow a larger degree of freedom for macromolecular transport around the obstacles that make up the medium than occurs in conventional electrophoresis media. 

Lambert O, Lev D, Ranck J-L, Leblanc G, Rigaud J-L. A new gel-like phase in dodecyl maltoside-lipid mixtures implications in solubilization and reconstitution studies. Biophys J1998 74 918-930. 

Polymerization of acrylonitrile adsorbed on polyacrylonitrile" An intimate mixture of polyacrylonitrile solvated by its monomer is obtained if one melts acrylonitrile crystals which have been subjected to high energy radiation at low temperatures. The polymer forms under irradiation within the crystal lattice and upon melting, a gel-like phase is obtained in which the individual polymer molecules do not aggregate, presumably because most of the CN groups are then associated in pairs with the -CN groups of the monomer. Such a polyacrylonitrile solvated by its monomer should indeed be an ideal medium for the matrix effect to operate. 

The solution with the precipitant was gently warmed to 45°C to redissolve the precipitate and gradually cooled in the thermostat. Phase separation took place after a while, and the phases were Isolated from each other by filtration. The gel like phase thus Isolated was the first primary fraction. The subsequent fractions were Isolated in the same way by the further successive additions of precipitant to the solution. The last fraction was Isolated by the addition of a large volume of the precipitant and allowing the solution to stand for 72 hours before the phase separation is affected by filtration as stated above. 

Vibrational spectroscopy shows that inclusion of cholesterol in phospholipid bilayers tends to decrease the fluidity of the hydrophobic region above the main transition point Tm and to increase it below Tm. The presence of cholesterol in DPPC or DMPC muti-layered vesicles does not affect the transition point but simply broadens the transition by decreasing the CH2-stretching wavenumber in the liquid crystalline phase and by increasing it in the gel-like phase (Lippert and Peticolas, 1971 Spiker and Levin, 1976 Casal and Mantsch, 1984). There is also evidence that lipid-cholesterol interaction increases the amount of bound water in the headgroups (Levin et al., 1985). 

Pressure filtration of the liquid is very difficult due to the complex interaction of the char and pyrolytic lignin, which appears to form a gel-like phase that rapidly blocks the filter. Modification of the liquid micro-structure by addition of solvents such as methanol or ethanol that solubilise the less soluble constituents will improve this problem and also contribute to improvements in liquid stability as described below. 

C02 is the cornerstone - either as primary substrate in photosynthesis for the anabolism of organic materials or as terminal product of their catabolic degradation - of the immense variety of bio-organic chemistry in living matter. These processes occur mainly in aqueous liquid or gel-like phases and are catalyzed by numerous enzymes. 

In a very recent work Prosa et al. [112] obtained a metastable form of stereoregular POT and PDoDT from m-xylene solutions. Whereas removal of the solvent by evaporation at 60° C gave the normal type of materials described in Section 4.3, evaporation at room temperature gave rise to a gel-like phase, which after a couple of days developed into a flaky brittle material, whose x-ray diffraction pattern turned out to be very different from that of the normal types. Heating to temperatures above 75°C led to an irreversible transformation into the normal form. 

Although biogenic silica exhibits no long-range crystallographic order (as determined by ultra high resolution transmission electron microscopy and diffraction methods,morphological order exists at the microscopic level. The initial distinction that can be made is between gel, continuous, and particulate structures. In true gel-like phases such as costal strips from the... 

The model proposed by Tu and Ouano [43] for polymer dissolution assumes Fickian solvent penetration into the polymer. The polymer dissolution problem was modeled as a multi-phase Stefan problem [44], The key parameter in this model was the disassociation rate, R, which was defined as the rate at which the polymer transformed from a gel-like phase to a solution. It was proposed that the dissolution process was disassociation -controlled if the polymer diffusion rate in a liquid layer adjacent to the solvent-polymer interface was faster than the disassociation rate, or diffusion -controlled if the diffusion rate was slower than the disassociation rate. 

As the polymer chains disentangle, they move out of the gel-like phase to a liquid solution through a diffusion boundary layer of thickness 5 (assumed to be constant in the present approach). The chain transport through this boundary layer is described as... 

Fig.2). At high density, the surface film is in a state thought of as a homogeneous liquid condensed or gel-like phase, LC, and finall) at ks,As a second-order phase transition to a solid condensed state SC occurs. Depending on the subphase temperature, not all of the phases shown in the schematic, Fig.2, are actually observed in the measurement, Fig.l. Rather, at low temperatures (T < 20 C) a transition from the gaseous to the condensed state (an ogous to a three-dimensional sublimation) occurs, whereas at high temperatures (T > 50 °C) the surface film remains in the expanded state,and no condensation occurs at all.

First I want to draw attention to polymers wherein specific solute-solvent interactions do promote mesophase formation. There are two general classes of polymer-solvent systems wherein instances of mesomorphism result from intermolecular interactions that are closely related to those that stabilize the amphiphilic MLC lyotropics DSidechain polymers with amphiphilic sidechains appended to the polymer backbone may form lyotropic PLCs in water, 2) Block copolymers exhibit organized, gel-like phases when one block is preferentially solvated. The former PLCs are intimately related to lyotropic MLCs, however, compared to the monomer amphiphiles, new phases and often phase stability is influenced by the attachment of the amphiphilic core to the chain. Finkelmann and co-workers have recently considered such amphiphilic sidechain PLCs.(17)... 

The literature data on kinetics and mechanisms of BaTiOs formation under hydrothermal conditions are contradictory. In general, the precursor of Ba is completely soluble in aqueous solutions, while the Ti precursor usually forms solid gel-like phases with low solubility. Since Ba + is not a gel forming ion, it initially adsorbs on the particles surface and dissolves in the gel of titanium compounds, destroying Ti-O-Ti bonds. This is accompanied by dehydration, followed by crystallization of perovskite phase via heterogeneous nucleation and growth [82, 83, 89-93]. 

Tablet Critical concentration (wt%) of 19-22 for the formation of the gel-like phases [46]...

Fig. 12 A model for gel-like phases of 19 and 20 in hydrocarbon. Reprinted with permission from Chem Eur J 2002, 8, 2143...

Most marketed CAPB solutions contain -30% active matter. This is, primarily, because aqueous betaine solutions form viscous, gel-like phases at slightly higher concentrations. In contrast to the situation for surfactants like lauryl ether sulfates, fluid mesophases consisting of CAPB, NaCl, and water do not exist at higher concentrations. The critical concentrations above which nonflowable gel phases are formed partly depend on the length of the fatty acid alkyl chains. 

G. Gottarelli, G. P. Spada, and E. Castiglioni, Circular dichroism for studying gel-like phases, in Molecular Gels. Materials with Self-Assembled Fibrillar Networks, eds R. G. Weiss and P. Terech, Springer, Netherlands, 2006, pp. 431-446. 

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