Critical dissolution temperature

Systems with a lower critical dissolution temperature include ... 

Systems with an upper and lower critical dissolution temperature include nicotine-water (60 and 218 C, Fig. 4C). 

In the majority of cases the solubility of one solvent in another increases until complete miscibility occurs at the UCST, otherwise known as the critical dissolution temperature or the consolute temperature (Table 13.9 and Fig. 13.5). 

TA1 Tager, A.A., Andreeva, V.M., Vshivkov, S.A., and Terent eva, V.P., Determination by the light scattering method of the position of the polystyrene-cyclohexane system spinodal near the lower critical dissolution temperature (Russ.), Vysokomol. Soedin., Ser. B, 18, 205, 1976. 

Equations (115)—(117), indicate that under the conditions just described, 8Tc/8x2 is both large and positive, as desired i.e., dissolution of a small amount of component 2 in the 1-3 mixture raises the critical solution temperature, as shown in the upper curve of Fig. 27. From Prigogine s analysis, we conclude that if component 2 is properly chosen, it can induce binary miscible mixtures of components 1 and 3 to split at room temperature into two liquid phases having different compositions. 

Considering the rather complicated processes that take place during dissolution it is not surprising that some systems show peculiar behavior. For example, while solubility generally increases with temperature, there are also polymers that exhibit a negative temperature coefficient of solubility in certain solvents. Thus, poly(ethylene oxide), poly(N-isopropylacrylamide), or poly(methyl vinyl ether) dissolve in water at room temperature but precipitate upon warming. This behavior is found for all polymer-solvent systems showing a lower critical solution temperature (LCST). It can be explained by the temperature-dependent... 

Using this approach, hydrophilic (neutral or ionic) comonomers, such as end-captured short polyethylene oxide (PEO) chains (macromonomer), l-vinyl-2-pyrrolidone (VP), acrylic acid (AA) and N,N-dimethylacrylamide (DMA), can be grafted and inserted on the thermally sensitive chain backbone by free radical copolymerization in aqueous solutions at different reaction temperatures higher or lower than its lower critical solution temperature (LCST). When the reaction temperature is higher than the LOST, the chain backbone becomes hydrophobic and collapses into a globular form during the polymerization, which acts as a template so that most of the hydrophilic comonomers are attached on its surface to form a core-shell structure. The dissolution of such a core-shell nanostructure leads to a protein-like heterogeneous distribution of hydrophilic comonomers on the chain backbone. 

Phase dissolution in polymer blends. The reverse process of phase separation is phase dissolution. Without loss of general validity, one may assume again that blends display LCST behavior. The primary objective is to study the kinetics of isothermal phase dissolution of phase-separated structures after a rapid temperature-jump from the two-phase region into the one-phase region below the lower critical solution temperature. Hence, phase-separated structures are dissolved by a continuous descent of the thermodynamic driving force responsible for the phase separation. The theory of phase separation may also be used to discuss the dynamics of phase dissolution. However, unlike the case of phase separation, the linearized theory now describes the late stage of phase dissolution where concentration gradients are sufficiently small. In the context of the Cahn theory, it follows for the decay rate R(q) of Eq. (29) [74]... 

There have been a number of physicochemical studies on the organic solutions of metal soaps and the critical solution temperature has been determined for a metal soap-organic solvent pair below this temperature we observe no appreciable dissolution of the metal soap, while above this particular temperature, dissolution becomes appreciable. According to these studies, metal soaps are in the form of micelles composed of several formula units of metal carboxylate, and the composition of the solute species was said to be indefinite (78a, 94). 

A temperature 85°C is higher than the critical crystallization temperature [33] of n-octadecanol monolayer. This means that the highest surface concentration of the monolayer, irrespective of the amount of n-octadecanol deposited on silica gel, is equal to 0.27 nm per molecule. The run of Vs vs r diagram for n-octane is slightly different from that at 40°C. The retention volumes increase with r up to a surfaee concentration 0.57 nm, but without a noticeable effect of silica gel surface deactivation, and next decrease to a minimum at r corresponding to 0.27 nm per n-octadecanol molecule, i.e. at the surface concentration characteristic for LE phase. The Vs increase beginning from this value is the result of n-octane dissolution in liquid threedimensional n-octadecanol. 

Fig. 11-1. Global mean conditions in the world ocean for the following quantities potential temperature 6 (i.e., temperature corrected for adiabatic heating), salinity, concentrations of total C02 and CO, and total alkalinity. [Adapted from Takahashi el al. (1981a).] Dashed curves indicate the spread of total C02 and alkalinity long-dashed curves show the critical dissolution regions for calcite and aragonite according to Broecker and Takahashi (1978).

Temperature can also be used as an acceleration factor in a fashion similar to potential. Many materials wiU not pit at a temperature below a critical value that is often extremely sharp and reproducible [56-62]. At low temperatures, extremely high breakdown potentials are observed, corresponding to transpassive dissolution, not localized corrosion. Just above the critical pitting temperature (CPT), pitting corrosion occurs at a potential that is far below the transpassive breakdown potential. This value of CPT is independent of environmental parameters and applied potential over a wide range, and is a measure of the resistance... 

The Krafft point is the temperature at which the solubility of hydrated surfactant crystals increases sharply with increasing temperature and forming micelles. This increase is so sharp that the solid hydrate dissolution temperature is essentially independent of concentration above the critical micelle concentration (cmc) and is therefore often called the Krafft point without specifying the surfactant concentration. The steep increase in solubility above the sharp bend is caused by micelle formation. Micelles exist only at the temperature designated as the Krafft point. This is a triple point at which surfactant mole-... 

Figure 5.18 Apparent diffusion coefficient for phase dissolution (squares) and phase separation (circles) as a function of annealing temperature. The lower critical solution temperature (LCST) is shown by the arrow.

Eluent gradient adsorption chromatography is one of the main HPLC techniques used in polymer fractionation including deposition-dissolution, chromatography under critical conditions, temperature gradient adsorption LC and precipitation dissolution LC [24-30]. 

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