Qualities of solvents

The second virial coefficients measured in various solvents at room temperature after heating are given in Table I. In the absence of aggregation and selective adsorption, a ranking by quality of solvents for PVB would follow the order of A2 values. The higher A2, the better the solvent. However, since these effects were not completely absent in the data used to construct Table I (particularly in the 9 1 solvent mixture), the solvent ranking given in this table must be considered tentative. 

Intrinsic Viscosity. Due to the complicating effects of aggregation and selective adsorption on the A2 values determined by light scattering, another means was sought to characterize the quality of solvents for PVB. The alternate means chosen was intrinsic viscosity measurements. Theory relates the intrinsic viscosity to the polymer chain dimensions through the expression (24)... 

The quality of solvent (i.e., solvent-polymer interactions) can also clearly affect the interaction forces. In a good solvent, polymer segments favor contacts with the solvent. Since the compression of the polymer layer by an approaching surface tends to squeeze out the solvent and force segment-segment interactions, the net result is a repulsion. In contrast, poor solvents produce an opposite effect, and a net attraction is possible for certain range of compression (see Section 13.6b). 

Let us first consider the case of salt-free one-component solvent (n, = 0). The dependences of the swelling parameter a on the value of x which characterize the quality of solvent for different values of a and O are shown in Fig. 1 [20]. 

Pig. 1. Dependence of the swelling parameter, a, on the quality of solvent, x, for polyelectrolyte (/), intermediate (2) and isoelectric (3) networks swelling in a salt-free one-component solvent... 

Fig. 2. Dependence of the swelling parameter, a, on the quality of solvent, x, for polyelectrolyte networks (m = 86, a, = a = 11) swollen in solutions of lo w-molecular-weight salt of concentrations n,a3 = 0 (/), 0.001 (2), 0.004 (. ), 0.01 (4). The dashed line corresponds to an electroneutrai network. Reproduced from Ref. [27]...

Kulicke, W. M., and Haas, R. (1984). Flow behavior of dilute polyacrylamide solutions through porous media. 1. Influence of chain length, concentration, and thermodynamic quality of solvent, lnd. Eng. Chem. Fund. 23 308-315. 

Ionic and covalent centres usually coexist [143], and their equilibrium proportions are a function of temperature, counter-ion type, quality of solvent and conversion. 

The quality of solvents and inorganic salts is an important consideration. Soluble impurities can give noisy baselines and spurious peaks or can build up on the surface of the packing material, eventually changing chromatographic retentions. Furthermore, the eluate may need to be collected for further analysis (e.g. mass spectrometry) and all contamination must be avoided. In addition, particulate matter should be removed, otherwise pump filters, meshes, and tubing can become blocked. 

Solvents The quality of solvents used in the MS analysis is very important, as contaminants can be detected during the analysis and cause severe problems. It is unusual for manufacturers to perform an MS analysis of solvents and it is advisable to try several sources of acetonitrile, water, and particularly formic acid to find suitable reagents. 

Discontinuous and continuous collapse of PCEPAC and poly(carboxyethyl 3-cyclohexylaminocrotonate) (PCECHAC) hydrogels was observed [221] in water/acetone and water/ethanol mixtures (Fig. 4). These results confirm the universal behavior of hydrogels with respect to the thermodynamic quality of solvents. 

The quality of solvent, reflected in the excluded volume v, enters only in the prefactor, but does not change the value of the scaling exponent u for any v > 0. The Flory approximation of the scaling exponent isu = 3/5 for a swollen linear polymer. For the ideal linear chain the exponent = 1/2. In the language of fractal objects, the fractal dimension of an ideal polymer is V — l/i/ = 2, while for a swollen chain it is lower T> — I/u = 5/3. More sophisticated theories lead to a more accurate estimate of the scaling exponent of the swollen linear chain in three dimensions ... 

The overlap concentration decreases with chain length more rapidly than in -solvent, with 4> since the exponent v = 0.588. The quality of solvent and the excluded volume increase with temperature and therefore,... 

Above the critical point (r > rcr), the size of the polymer gel slightly depends on the quality of solvent and is determined by the balance of the elastic free energy and the osmotic pressure of the counterions ... 

The exponent a depends on the quality of solvent (good solvent with high degree of swelling a = 3/5 poor solvent a = 3/8). 

Solvents may be recovered and reused in the same process or in different processes, provided that the recovery procedures are validated to ensure that recovered solvents meet appropriate standards before reuse or commingling with other approved materials. The quality of solvent mixtures should be monitored at suitable intervals. 

The quality of solvent or the cosolvent action has been established by determining the magnitude of the miscibility range between the two critical temperatures, UCST and LCST. The application of pressure can widen the miscibility range. ... 

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