Solvents as a Function of Temperature

Final adjustment of solvent selection must be done under actual field conditions. In many baking coatings a significant fraction of the solvent is lost in the baking oven, yet the tables of relative evaporation rates are based on 25°C air. Information on evaporation rates for a small number of solvents as a function of temperature up to 150°C has been published (73). 

What are the consequences What is the maximum pressure Vapor pressure of solvent as a function of temperature Gas evolution Differential Thermal Analysis (DTA) / Differential Scanning Calorimetry (DSC) Dewar flask experiments... 

Fig. 6.1. Vapor pressures of solvents as a function of temperature. 1 glycerin, 2 DMSO (C3Hg03), 3 water, 4 ethanol, 5 aceton.

Strambini and Galley have used tryptophan anisotropy to measure the rotation of proteins in glassy solvents as a function of temperature. They found that the anisotropy of tryptophan phosphorescence reflected the size of globular proteins in glycerol buffer in the temperature range -90 to -70°C.(84 85) Tryptophan phosphorescence of erythrocyte ghosts depolarized discontinuously as a function of temperature. These authors interpreted the complex temperature dependence to indicate protein-protein interactions in the membrane. 

Observations carried out on lysozyme in mixed solvents as a function of temperature demonstrate that lysozyme-catalyzed lysis can he performed under such abnormal conditions and that the reaction can be quenched at subzero temperatures and resumed by heating. The problem is now to check whether one can obtain an enzyme-substrate complex (in this case lysozyme-oligosaccharide) stabilized at low temperature. Such a complex can be detected by differential absorption spectroscopy. Difference spectra in the UV region (240-320 nm) were recorded. The reference cell contained a solution of lysozyme (1.39 x 10 M) and the sample cell contained a solution of lysozyme at the same concentration plus substrate, here hexa-NAG (1.66 x lO " M). The buffer used is acetate at pH 5 plus organic solvent. Also, difference spectra have been determined in the presence of the small-chain sac-... 

We have seen that crystals can be safely transferred to mixed solvents and that the percentage of organic solvent may often be increased to any desired level provided that its gradual addition is coupled with a gradual reduction in temperature so as to keep the dielectric constant of the medium as near as possible to the value for the normal mother liquor. Such a result deserves explanation and comment about the behavior of the dielectric constant in mixed solvents as a function of temperature. 

Oa-Consumption, in milliliters of 02 per minute, in Rose Bengal-Sensitized Photooxygenation of a-Terpinene in Different Solvents as a Function of Temperature (from ref. 124) ... 

It will have been obvious from the previous discussion that the data available for eosin and proflavine hydrochloride are far less complete than could be desired. More extensive data in various solvents as a function of temperature (including the region below 77 °K.) would allow more reliable values of intersystem crossing rates to be calculated. It would be interesting to compare these rates for a variety of dyestuffs, or... 

Titration of Proteins in Mixed Solvents as a Function of Temperature... 

Potentiometric titration in mixed solvent as a function of temperature indicates the AH of the p/ of the cytochrome c is —9.4 kcal mol-1. Thus AH buffer < AH of pZ of protein. 

Thermogelation of a Two-Component Mixture. The simplest procedure for obtaining a microporous system is the thermogelation of a two component mixture. At a specific temperature, the mixture forms a homogeneous solution for all compositions but at a tower temperature shows a miscibility gap over a wide range of compositions. This behaviour is illustrated schematically in Figure 1, which shows a phase diagram of a two component mixture of a polymer and a solvent as a function of temperature. 

Figure 10. CD spectrum of pentaammine (S)-2-chloropropionato cobalt(III) tet-raphenylborate in various solvents as a function of temperature...

Fig. 6.7. Effect of added soiute on the chemical potential of a liquid solvent as a function of temperature. The freezing point is depressed and the boiling point is elevated.

The most extensive series of studies in this area are those of Ben-Naim and co-workers.They have measured the solubilities of argon in various mixed solvents as a function of temperature, and calculated free energies, enthalpies, and entropies of solution. All data are presented in graphical form, and include the solvent systems, water-ethanol, water-p-dioxan, and water-methanol. The last two of these systems were studied over the entire concentration range, and while the primary interest was in aqueous and highly aqueous mixed solution, useful information is given on organic systems. 

The expression provides a criterion to predict whether or not the mixed solvent is expected to be a cosolvent of the polymer. When T, is a UCST (as is the case in these phase separation studies), -dx /dT > 0 and (dTc/dx)o has the same sign as the numerator of the equation. Choosing solvent 1 such that T 2 < T, then (dTc/dx)o < 0 guarantees that the system will be a cosolvent one. Since %23 - Zi3 > 0, at T i, the numerator in the equation [5.4.1] is negative (cosolvent system) if the unfavorable interaction between the two liquids is large enough to compensate for their different affinity towards the polymer. The equation proposed gives a more detailed criterion for cosolvency than the simple criterion of G > 0. The information needed to predict (dTydx)o from equation [5.4.1] includes the binary interaction parameters of the polymer in each one of the two solvents as a function of temperature, and Xi2(G ) for the mixed solvent too. Table 5.4.1 summarizes results reported by Horta et al. for some cosolvents of polymethylmethacrylate (PMMA). ... 

Figure 5.62 Henry constants of various gases in organic solvents as a function of temperature. Experimental data from [3]. hydrogen in benzene, A hydrogen in cyclohexane, methane in methanol, carbon dioxide in toluene.

Experimental work is consistent with the view that solvent specific corrections to the intramolecular potential are not required in the absence of strong polymer/solvent interactions. Glowinkowski et al. used CNMR to study the local dynamics of polyisoprene in ten solvents as a function of temperature [31]. They measured correlation times due to the motion of differmt C-H vectors in the chain backbone. They found that these correlation times were determined by oidy the temperature and the solvent viscosity. Variables such as solvent shape, flexibility, and chemical functionality had no effect on the correlation times, except through the solvent viscosity. (Highly polar solvents were excluded from this study as they do not dissolve polyisoprene.) Similar conclusions have been reached in NMR studies of polybutadiene [52] and in time-resolved optical studies of polyisoprene [53] and polystyrene [54] with anthracene labels. NMR studies of PEO [55] have been interpreted as supporting this same conclusion [31] (except when the solvent was water [56]). 

This review article contains selected values for the solubility, entropy, and enthalpy changes in solution for 16 gases in 39 non-aqueous solvents. Also given are the coefficients of polynomial expressions for the Gibbs energy of solution for a gas in a given solvent as a function of temperature. See also item [8]. 

Density data for the pure solvent as a function of temperature... 

FIGURE 2.26 The estimated solubility parameter distance, Ra, of (bisphenol A) polycarbonate (MW = 100,000) with three common solvents, as a function of temperature. 

The kinetics of the release of Cs+ from its complexes with (3), (8), and two cryptands [(9) and (10)] have been measured in various solvents as a function of temperature by Cs n.m.r. spectroscopy. The activation enthalpy is substantially larger in the case of the cryptates than for the crown ether complexes (Table 6) but this is more than compensated by a favourable entropy of activation. Similar high values of A/T were obtained for the dissociation of Na+ from its complex with (10) in various solvents (Table 7) but in this case the sign of A5 was generally negative. 

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