Solubility-temperature relationship, for

The solubility of starch increases monotonically with the heating time for temperatures of 150 to 175 °. At temperatures between 200 and 213°, maximum solubility is reached, followed by a decrease interpreted as the result of secondary reactions of retrogradation of oligosaccharides formed in the first step of dextrinization. Excellent evidence for the solubility-temperature relationships for three different starches was given by Cer-niani (see Table XIV). 

The solubility-temperature relationship for 1 hofheating of starch, with nitric acid as the catalyst, is presented in Fig. 11. The solubility of dextrins formed can be influenced by contact with the atmosphere. Vacuum, as well as air flow, favor the presence of soluble matter in dextrinized starch (see Fig. 12). However, the effect observed may be attributable to continuous removal of moisture. On the other hand, the results of the present authors showed that the course of dextrinization under nitrogen, carbon dioxide, and in air yields different dextrins of various solubility and stability after a given period of dextrinization. 

The excess heats of solution of a liquid solute in the two equilibrium phases are just its heats of solution in the two phases, which may be determined from the solubility-temperature relationships. For solid solutes, the excess heats of solution are the heats of solution of their supercooled liquids, which are less than Ae heats of solution of solids by an amount equal to the heat of fusion, A f. However, as long as the (solid) solute does not reduce its melting point in the solvent, the difference in excess heats between the twojolvent phases is the same as that between the heats of solution, because the A//f term cancels. Equation (14) may therefore be expressed for both liquid and solid substances as... 

The solubility-temperature relationship for nonionic surfactants shows a different behavior from ionic surfactants. Figure 20.6 shows the phase diagram of Ci2E06-The nonionic surfactant forms a clear solution (micellar phase) up to a certain temperature (that depends on concentration) above which the solution becomes cloudy. This critical temperature, denoted as the cloud point (CP) of the solution, decrease with increase in surfactant concentration reaching a minimum at a given concentration (denoted as the lower consolute temperature) above which the CP increases with further increase in surfactant concentration. Above the CP curve the system separates into two layers (water -I- solution). Below the CP curve, several liquid crystalline phases can be identified as the surfactant concentration exceeds a certain limit. Three different liquid crystalline phases can be identified, namely, the hexagonal, the cubic, and lamellar phases. A schematic picture of the structure of these three phases is shown in Fig. 20.7. 

Solubility-temperature relationship(s) sodium with other elements, 22 763 for surfactants, 24 125-126... 

Temperature Effect. Near the boiling point of water, the solubility—temperature relationship undeigoes an abmpt inversion. Over a narrow temperature range, solutions become cloudy and the polymer precipitates the polymer cannot dissolve in water above this precipitation temperature. In Figure 4, this limit or cloud point is shown as a function of polymer concentration for poly(ethylene oxide) of 2 x 106 molecular weight. 

One of the characteristic features of solutions of surfactants is their solubility-temperature relationship, which is illustrated in Fig. 3 for an anionic surfactant, namely, sodium decyl sulfonate. It can be seen that the solubility of the surfactant increases gradually with an increase in temperature, but above 22°C there is a rapid increase in... 

Although amorphous pharmaceutical materials can be readily isolated and may persist for many thousands of years,they are in fact a thermodynamically metastable state and will eventually revert to the more stable crystalline form. Fig. 4 shows a snapshot in time of the free energy-temperature relationship for a material that can be isolated as both an amorphous form and a crystalline form. This quasi-equilibrium thermodynamic view of the amorphous state shows that the amorphous form has a significantly higher free energy than the crystalline form, and illustrates why it is expected to have a much higher aqueous solubility and significantly different physical properties (e.g., density). 

The foaming properties of the nonionic surfactants depend upon the temperature because of their inverse solubility temperature relationship. Above the cloud point they are nonfoamers and some nonionic surfactants may even function as defoamers above their cloud point temperature. Therefore, the nonionic surfactant selected for rinse aid formulations must have a cloud point below the temperature of the rinse water. 

Since all scale-forming constituents of saline waters have inverted solubility-temperature relationships, the scale problem can be alleviated, if not wholly solved, by evaporation at high vacuum and hence low temperature. Some small single-stage units for household and other uses boil the solution at a temperature as low... 

To understand how temperature influences the composition of crystals that form, it is useful to examine typical solubility-temperature diagrams for substances exhibiting monotropic and enantiotropic behavior [15], In Fig. la, Form II, having the lower solubility, is more stable than Form I. These two noninterchangeable polymorphs are monotropic over the entire temperature range shown. For indomethacin, such a relationship exists between Forms I and II, and between Forms II and III. 

The solubility characteristics of a given substance in a solvent chosen have considerable influence on the selection of a suitable crystallization technique. In case of a weak solubility-temperature relationship, (as e.g. for NaCl) cooling crystallization is of course not the method of choice. Otherwise, when the solubility curves of two compounds differ signiflcanfly, these specific characteristics can be used for separation. For example, in the well-known hot leaching process, potassium chloride as target compound is separated from its mixtures with sodium chloride using the differences in the solubility functions (Figure 3.22). 

The suspension is kept at constant temperature for at least the equilibration time teq already determined. Optimal mixing of the suspension should be examined repeatedly during equilibration. Slight inaccuracies of the temperature affect the correctness of the solubility value in particular for strong solubility-temperature relationships. 

The Kraft point (T ) is the temperature at which the erne of a surfactant equals the solubility. This is an important point in a temperature-solubility phase diagram. Below the surfactant cannot fonn micelles. Above the solubility increases with increasing temperature due to micelle fonnation. has been shown to follow linear empirical relationships for ionic and nonionic surfactants. One found [25] to apply for various ionic surfactants is ... 

In this approach, connectivity indices were used as the principle descriptor of the topology of the repeat unit of a polymer. The connectivity indices of various polymers were first correlated directly with the experimental data for six different physical properties. The six properties were Van der Waals volume (Vw), molar volume (V), heat capacity (Cp), solubility parameter (5), glass transition temperature Tfj, and cohesive energies ( coh) for the 45 different polymers. Available data were used to establish the dependence of these properties on the topological indices. All the experimental data for these properties were trained simultaneously in the proposed neural network model in order to develop an overall cause-effect relationship for all six properties. 

The derivation of the quantitative relationship between this equilibrium temperature and the composition of the liquid phase may be carried out according to the well-known thermodynamic procedures for treating the depression of the melting point and for deriving solubility-temperature relations. The condition of equilibrium between crystalline polymer and the polymer unit in the solution may be restated as follows ... 

Marshall, W.L., Slusher, R. and Jones, E.V. (1964b) Aqueous systems at high temperatures, XIV Solubility and thermodynamic relationships for CaSOa in NaCl-H20 solutions from 40°C to 200°C, 0 to 4 molal NaCl. J. Ghent. Eng. Data, 9, 187-191. 

Gtickel, W., Kastel, R., Lawerenz, J., Synnatschke, G. (1982) A method for determining the volatility of active ingredients used in plant protection. Part III The temperature relationship between vapour pressure and evaporation rate. Pestic. Sci. 13,161-168. Hafkenscheid, T. L., Tomlinson, E. (1981) Estimation of aqueous solubilities of organic non-electrolytes using liquid chromatographic retention data. J. Chromatogr. 218, 409 -25. 

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