GEL TEMPERATURE

Table 2. Thermal behaviour of the gels. Temperatures [°C], where minimal storage moduli were observed on reheating. Concentrations of ions in mmol / lOOg gel, [V " ] = added bivalent ion, [Z ] = added monovalent ion, [C1 ] = 2.5, 2[V+ ]+[Z+]=2.5 or [Na ]+[K ]=2.5.

Note 1 A thermoreversible gel is usually formed by cooling a polymer solution. In these cases, the gel temperature is a maximum temperature at which the presence of network is observed. 

Note 2 Since gel temperatures depend on the method of determination, this should always be indicated. 

Polyacrylamide preparative gels usually run with a 0.5x or 1 X TBE buffer and require a power value around 2BWatts in denaturing conditions. The gel temperature... 

Calcium chloride has several industrial applications. The major applications of this compound are in deicing of roads, dust control, imparting stability to roads and buildings, and to improve traction in tractor tires. It is mixed with ice to make freezing mixtures. Hexahydrate mixed with crushed ice can lower the temperature of the cooling bath to below -50°C. It also is used as a desiccant for dehydrating gases and liquids. It is added to cement in various proportions to manufacture different types of concrete. Other uses are in adhesives, to lower gel temperatures, and as a calcium source in liquid feed supplements for dairy cattle. Also, the compound is used to control particle size development and reduce coalescence in plastics. 

Different grades of Methocel and Metolose are supplied, with nominal viscosities of 4000 mPa s (measured with a Brookfield viscometer on a 2% w/v solution). Methocel 4M types E and are different in their hydration rates, type being the quickest. Metoloses SH4000 differ in their gel temperature. Grades 60 and 90 were used. Another polymer of 4000 mPa s viscosity was used hydroxyethylcellulose, in order to observe effects on the dissolution rate. 

Heat Treatment Conditions. Because of very finite process constraints In the food processing Industry, the heat treatment required for gel formation Is extremely critical when assessing the applicability of a given protein to a specific food formulation. For example, replacement of myosin (which has relatively low gel temperature requirement) In a hot dog formulation with a protein preparation requiring extremely high temperature for comparable gelation would not be desirable. 

Cowperthwaite, Coe, and Frissell (J) in their viscosity/temperature studies have defined the temperature at which the plastisol viscosity begins to increase as the gel temperature. These authors also studied the tensile strength of films cast on glass plates, fluxed at a series of temperatures between 300° and 425°F. They have defined the temperatures at which tensile strengths of 1000 and 1500 p.s.i. are attained as the fluxing temperatures. ... 

The position of each component of a mixture is quantified by calculating the distance traveled by the component relative to the distance traveled by the solvent. This is called relative mobility and symbolized by Rf. In Figure 3.2D, the R values for components B and C are calculated. The Rf for a substance is a constant for a certain set of experimental conditions. However, it varies with solvent, type of stationary support (paper, alumina, silica gel), temperature, humidity, and other environmental factors. R values are always reported along with solvent and temperature. 

During vacuum drying, the gel will feel cold relative to the surrounding platen if it is not completely dry. When the gel temperature is the same as the platen, the gel is dry and the vacuum and dryer can be turned off. Gel cracking can be caused by releasing the vacuum before the gel is dry. 

When the gel has polymerized, the comb is removed and wells are flushed thoroughly with deionized (RNase-free) water. At this stage, the gel can be covered with plastic wrap and stored overnight at 4 °C, if desired. The binder clamps (and tape if used) are removed and the gel is placed on the gel box. The upper and lower reservoirs are filled with 1 x THEM and prerun for 30-45 min with the water bath at the desired temperature, making sure that the current is not blocked by ice, precipitate, or air bubbles. The gel temperature can be monitored with a contact thermometer or small thermal probe inside the gel. 

Reduced gel temperature for low moisture foods59 Improved emulsification properties25,66,67... 

Increased stability, broadened gel temperature range105 Reduced enthalpy104... 

Increased viscosity109 Increased process tolerance110 Increased gel temperature range... 

Poly(chloro-p-xylylenes) containing (in theory) about 5, 10, and 20% butyl-p-xylylene were prepared in this way (see illustration on p. 650). The crystalline melting points of the products (XVII) were in the range 220°-250°C. compared with 290°C. for pure poly (chloro-p-xylylene). Solubility characteristics of the products and a sample of poly (chloro-p-xylylene) were studied by heating in a-chloronaphthalene. The solution temperature is the minimum temperature required to dissolve the product with slow heating. The gel temperature is that at which the solution of the product in a-chloronaphthalene sets to a gel on gradual cooling. Results were as follows ... 

The amount of borax added has only a limited influence on the viscosity behavior of the low ash hemicellulose solutions (Figure 10). An increase in the amount of borax seems to increase the gel temperature somewhat. 

Entry Formula (daltons) Maxium Viscisity (Pa- s) Maxium Gel Temperature (°C)... 

Yuguchi, Y., Thuy, T., Urakawa, H., and Kajiwara, K. (2002). Structural characteristics of carrageenan gels temperature and concentration dependence. Food HydrocoUoids. 16(6), 515-522. 

It is known from Table 4 that the gel time increased with the fall of gel temperature and it is more difficult to form gel under lower temperature. 

The idea of gel point has received much attention in synthetic and biopolymer gels. One can talk about gel point as an instant in time or as a specific temperature. In this chapter, the symbols and Tgei will be used for the gel time and gel temperature (Tobitani and Ross-Murphy, 1997a Foegeding et al., 1998), respectively. One can imagine many qualitative definitions of gel point, especially based on visual observation of individuals. Here, however, methods based on rheological measurements are emphasized. 

Glass transition temperature of unfrozen solute-water phase, K Gel temperature, K... 

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