Formamide solubility parameter

The membrane conductivity of Nafion in various protic solvents has been measured in a recent study and the results are given in Table 12. The ratio of the membrane conductivity (k) to the solvent conductivity (k ) is listed in the last column of the table. A plot of the conductivity ratio (/solubility parameter of the solvent is shown in Fig. 22. The membrane conductivity is higher than the solvent conductivity in all solvents except formamide. 

In general, one can expect a high degree of interaction between materials that have solubility parameters differing by 4 (J cm ), although it is sometimes necessary to extend that range to 8 or 10 units. For example, a material (or group) with d = 39.3 (J cm ) (formamide) would be expected... 

Similar reasoning applies to mixtures of solvents. The combination of a nonsolvent with a lower, and a nonsolvent with a higher, solubility parameter than that of the polymer often gives a good solvent for the polymer (Table 6-4). Conversely, a mixture of two solvents can be a nonsolvent. Poly(acrylonitrile) 62 = 12.8), for example, dissolves in both dimethyl-formamide (<5i = 12.1) and malodinitrile = 15.1), but not in a mixture of the two. 

In the thermodynamics of polymer blends the solubility parameter is the most important parameter describing the miscibility between component polymers. However, this parameter is insufficient to explain the above finding. The samples were prepared in the form of film by casting from dimethyl formamide (DMF) solution. The values of solubility parameters are 14.7, 18.93, and 24,8x10 ... 

To assess the applicability of the modules in Materials Studio 4.2 that are relevant for this application, the COMPASS force field [25] was chosen as currently implemented in the Forcite molecular simulation engine. To test the accuracy of densities calculated in these atomistic simulations, benchmark calculations were performed for some experimentally weU-characterized traditional solvents either with some structmal similarity to the imidazolium cation (pyridine, methylimidazole) or for some specifically selected value of the solubility parameter components as will be shown later (CSj, formamide). The results of the simulations (which used 20 solvent molecules and followed the protocol described above) are presented in Table 5.1. 

Two Components of the Solubility Parameter of Formamide as Determined in Molecular Dynamics Simulations Using Charges Assigned by the COMPASS Force Field and Electrostatic Potential-Derived Charges along with the Experimental Values... 

FIGURE 5.6 Changes in the calcnlated components of the solubility parameter of formamide as a function of density of the simulation box using the values at the experimental density as reference. 

It can be seen in Figure 5.6 that even an almost 10% inaccuracy in the density introduces only a <2 unit (about 7%) change in the solubility parameters. Formamide was chosen for this test because it has both large van der Waals and electrostatic contributions and it is expected that the other molecular solvents are even less sensitive to changes in the density. 

Solvatochromic Approach Solvatochromic relationships are multivariate correlations between a property, usually solubility or partitioning property (see Sections 11.4 and 13.3), and solvatochromic parameters, parameters that account for the solutes interaction with the solvent. In the case of vapor pressure, the solvatochromic parameters only have to account for intermolecular interaction such as selfassociation between the solute (i.e., pure compound) molecules themselves. The following model has been reported for liquid and solid compounds, including hydrocarbons, halogenated hydrocarbons, alkanols, dialkyl ethers, and compounds such as dimethyl formamide, dimethylacetamide, pyridine, and dimethyl sulfoxide... 

From these data it is suspected that the molecules of the solvate structure of lithium ion might be largely effected by the solvent molecules. Since the solubility of some lithium salts is relatively high in MN-dimethyl formamide (DMF), concentrated solutions can also be examined. In a previous study the solvate structure of lithium has been described in an 1.5 mol dm LiNCS solution in DMF [38]. A new XD measurement has been carried out for a LiCl solution of the same concentration. Table 1 hows the structural parameters for the lithium solvates in both solutions. The structural parameters were determined by a least-squares fitting method (LSQ). After the subtraction of the contributions ascribed to the intramolecular stmcture of the DMF molecules and to the assumed structure around the anions from the total structure function of the solution, the resulted difference curve was approximated by calculated model curves. The result is shown in Figure 1. 

Physical Parameters. Metronidazole is obtained as cream-coloured crystals having mp 158-160°C. Its solubility at 20°C (g/100 ml) water 1.0 ethanol 0.5 ether < 0.05 and chloroform < 0.05. It is found to be sparingly soluble in dimethyl formamide (DMF) and soluble in diluted acids. The pH of a saturated aqueous solution stands at 5.8. 

Solution ProportiGS. The amide group (—CONH2) in poly(acrylamide) provides for its solubility in water and in a few other polar solvents such as glycerol, ethylene glycol, and formamide. We can acquire a sense of poly(acrylamide) s affinity for water by examining a few characteristic parameters. Theta ( ) conditions for a polymer delineate a particular combination of solvent and temperature at which the polymer acts in an ideal manner (22), ie, the chains behave as random coils. The 0 temperature of poly(acrylamide) in water has been determined to be -8°C (23). Thus, water at 25°C is a solvent of intermediate quality for poly(acrylamide). Aqueous methanol (40 vol%), however, is a solvent for poly(acrylamide) at 25°C (24). The Flory / parameter, which is a measure of the relative affinity between the polymer segments with each other vs with the solvent, is 0.5 under conditions. The Flory / parameter of poly(acrylamide) has been determined to be 0.48 in water at 30°C (25). These and other properties of poly(acrylamide) in solution are collected in Table 2. 

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