Gel characteristics

Besides pH, other preparative variables that can affect the microstructure of a gel, and consequendy, the properties of the dried and heat-treated product iaclude water content, solvent, precursor type and concentration, and temperature (9). Of these, water content has been studied most extensively because of its large effect on gelation and its relative ease of use as a preparative variable. In general, too Httie water (less than one mole per mole of metal alkoxide) prevents gelation and too much (more than the stoichiometric amount) leads to precipitation (3,9). Other than the amount of water used, the rate at which it is added offers another level of control over gel characteristics. 

The phenomenon of gelation is best understood by examining some typical gelling systems. Inasmuch as each gel presents peculiarities of its own, it is impossible to discuss every type available. The systems chosen for discussion show properties that illustrate important gel characteristics. 

Schwartz, R. W. 1989. Chemical processing of PbTi03 by co-precipitation and sol-gel methods the role of powder and gel characteristics on crystallization behavior. PhD dissertation. University of Illinois at Urbana-Champaign. 

On standing, both the initially distilled and redistilled material may deposit a small amount of flocculent solid or gel characteristic of polymerized material, which results in some thickening of the product oil. 

Slurry Viscosities. In addition to the yield stress, the characteristic shear stress-shear rate relation of the fuel slurry should be known since the shape of the shear rate-shear stress curve (consistency curve) is an indication of the gel characteristics. Low shear rate data (102 sec."1) are useful mainly in determining batch-to-batch reproducibility, while high shear rate data (104 to 106 sec."1) are required to assess the flow characteristics in engine hardware. 

Gels for quantitating gel characteristics were prepared In screw capped centrifuge tubes (22 X 100 mm) by heating at 100 C for 15 min C14, l, l, ). Gel strength was determined by a penetration technique using the Instron fitted with a disk probe (6.0 ran diameter) (15.16). Instrumental texture profile analysis on gel sections (1.5 X 1,0 cm) was done on an Instron fitted with a... 

Multiple regression and response surface analysis techniques were employed to assess the effects of cysteine and GaGl combinations on WPG gel characteristics (15). Gontour plots summarizing these data trends are presented in Figure 3. Significant interaction effects were observed between reagents with respect to hardness, cohesiveness and compressible water. At low levels of added... 

Table III. Dialysis effect on gel characteristics of 10% protein dispersions of whey protein concentrate (WPG) heated at 100 C for 15 rain.

Protein System Visual Hardness (Kg) 3 Gel Characteristics Gumminess (Kg) Chewiness (Kg-mm)... 

With the recent commercial availability of ultrafiltration, it has become possible to increase the concentration of casein, thus levelling out seasonal variations in milk composition and consequently in gel characteristics and... 

Diene substrate latices were prepared by seeding techniques following the scheme shown in Figure 1. Persulfate anion was the initiator, and an alkyl aryl sulfonate was the emulsifier. Reaction time varied between 13 and 33 hours. Since all the substrates were prepared by similar techniques, the volumetric swell index and gel gravimetric data (toluene) varied little with particle size. Small differences in swell and gel characteristics should not be a variable in this study because of the polarity of the grafting monomer mixture and rapidity of the graft reactions. 

A single polysaccharide can rarely optimize all the requisites of a fat, so the trend has been toward combinations, e.g., konjac-carrageenan blends in lean meat and sausages (FMC, 1991). Simulation should be more achievable by the use of cosolutes with complementary sol-gel characteristics. The... 

The amount of water used in sol-gel preparation and the rate by which it is added also influence gel characteristics. The former is usually expressed in terms of the hydrolysis ratio h, defined as the moles of water per mole of metal alkoxide, M(OR)m. There are three specific regions of interest [4] ... 

Hermansson, A.M. (1982). Gel characteristics Structure as related to texture and water binding of blood plasma gels. J. FoodSci. 47, 1965-1972. 

Twenty years after the appearance of Klebe and Murray s patent, the applicability of PSCs as precnrsors for Si-C-N ceramics was discovered. Riedel et al. ° fonnd that analogons to aUcoxysilanes, pyridine-catalyzed reactions of chlorosilanes and bis(trimethylsilyl)carbodiimide possess typical sol-gel characteristics (Fignre 18.4). ° ... 

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