Free energy parameter

SAN resins show considerable resistance to solvents and are insoluble in carbon tetrachloride, ethyl alcohol, gasoline, and hydrocarbon solvents. They are swelled by solvents such as ben2ene, ether, and toluene. Polar solvents such as acetone, chloroform, dioxane, methyl ethyl ketone, and pyridine will dissolve SAN (14). The interactions of various solvents and SAN copolymers containing up to 52% acrylonitrile have been studied along with their thermodynamic parameters, ie, the second virial coefficient, free-energy parameter, expansion factor, and intrinsic viscosity (15). 

Valko et al. [37] developed a fast-gradient RP-HPLC method for the determination of a chromatographic hydrophobicity index (CHI). An octadecylsilane (ODS) column and 50 mM aqueous ammonium acetate (pH 7.4) mobile phase with acetonitrile as an organic modifier (0-100%) were used. The system calibration and quality control were performed periodically by measuring retention for 10 standards unionized at pH 7.4. The CHI could then be used as an independent measure of hydrophobicity. In addition, its correlation with linear free-energy parameters explained some molecular descriptors, including H-bond basicity/ acidity and dipolarity/polarizability. It is noted [27] that there are significant differences between CHI values and octanol-water log D values. 

This form of the temperature dependence supports the idea that % is fundamentally a Gibbs free energy parameter with entropic and enthalpic parameters. 

In the simulations, the free energy parameters / are unknown. However they can be obtained by solving (6.82) and the following equation self-consistently ... 

The mixed cmc behavior of these (and many other) mixed surfactant systems can be adequately described by a nonideal mixed micelle model based on the psuedo-phase separation approach and a regular solution approximation with a single net interaction parameter B. However, the heats of micellar mixing measured by calorimetry show that the assumptions of the regular solution approximation do not hold for the systems investigated in this paper. This suggests that in these cases the net interaction parameter in the nonideal mixed micelle model should be interpreted as an excess free energy parameter. 

The parameters AVg (acidity), AVg (basicity), pK, and Zo represent properties of solute in the bulk solution phase. If reverse osmosis separation is governed by the property of solute in the membrane-solution interface, the existence of unique correlations between data on reverse osmosis separations and those on the above parameters, means that the property of solute in the bulk solution phase and the corresponding property of solute in the membrane-solution interface are also uniquely related. This leads one to the development of interfacial free energy parameters (-AAG/RT) for both nonionized solute molecules and dissociated ions in solution for reverse osmosis systems where water is preferentially sorbed at the membrane-solution interface. 

Figure 7. Experimental data on the effect of (a) Taft s number for alcohols and (b) interfacial free energy parameter for ionized inorganic solutes on their reverse osmosis separations in systems involving dilute aqueous solutions and cellulose acetate membranes (9 15, 37, 38 ...

The normalized spectroscopic parameters of aqueous... 

For the pressure studies, two phase" compact ion behavior is observed with an inflection point between 7 and 11 atms. For the aqueous solution studies, the hydraulic permeability K and the g-ratio are hardly effected by solute type (within experimental error). The solute diffusive permeability however, varies with solute type in good qualitative agreement with free energy parameters, infrared overtone shifts, and spin echo and continuous wave nuclear magnetic resonance spectroscopy results from the literature. 

The main object of the theory is to find from the analysis of the simplest model which of free-energy parameters are and which are not significant. It is also... 

Freier, S., Kierzek, R., et al. (1986). Improved free-energy parameters for predictions of RNA duplex stability. Proc. Natl. Acad. Sci. USA 83(24), 9373—9377. 

In this particular example, estimates for both free energy parameters g and ga of the coarse-grained model are obtainable from more detailed molecular models albeit that strictly speaking they depend not only on the chemical composition and structure of the molecular building blocks but in principle also on the solvent properties. It is important to stress again for it is often ignored, the solvent molecules not only drive the assembly but have been shown to play an active role in structural reorganizations of supramolecular assemblies (Bouteiller et al., 2005 Jonkheijm et al., 2006). Ideally, their influence should not be absorbed in adjustable parameters as is almost always done. 

As can be seen, X is a dimensionless free-energy parameter which is sometimes called a generalized interaction parameter. 

To discuss the phase stability of polymer blends in more detail one has to specify the free-energy parameter X. This can be done in terms of an equation-of-state theory [8]. Theories that take into account the compressible nature of the pure components as well as that of the mixture are called equation-of-state theories. As basic quantities characterizing the thermodynamic state of a system the reduced temperature (T), volume (V) and pressure (P) are employed and defined by... 

As mentioned before, Eq. (3) reveals that the parameter X is a free-energy parameter comprising an enthalpic part XH and an entropic part Xs ... 

A is the solvent-accessible surface area of the fth group (computed with the algorithm of Reference 96), a, is an empirically derived free energy parameter for the /th group, and N is the number of groups in the oligopeptide. 

A. Verloop, Drug. Des., 3,133 (1972). The Use of Linear Free Energy Parameters and Other Experimental Constants in Structure-Activity Studies. 

Fig. 4.2a-c. Experimental, eap (dotted histograms), and theoretical, theo hydrogen-bond length distributions, a For C=0 H-N, b for C=O H-0. Number of experimental data are 151 and 47 for a and h, respectively. ptheo,corr s obtained with correction of the free energy parameters, assuming a one-dimensional model of the hydrogen bond... 

One can then attempt to relate the free energy of the reaction (or the equilibrium constant or the redox potential) of the one-electron step to the rate of the reaction. Extensive tabulations of one-electron redox potentials have recently become available (e.g., Wardman, 1989). Often it is possible to relate rate constants to free energy parameters (AG , K, pe°) in a series of related redox reactions (e.g., oxidation of ions of transition elements with O2, H2O2, Mn02, etc.) or redox reactions involving organic compounds with var-... 

Verloop, A., The use of linear free energy parameters and other experimental constants in structure-activity studies, [n Drug Design (E. J. Afiens, ed.) Academic Press, New York, 1972. 

Blends of polystyrene/poly(2,6-dimethyl-l,4-phenylene oxide) and polystyrene/poly(vinyl methyl ether) were investigated by IGC over wide composition and temperature ranges. Flory-Huggins free energy parameters were obtained and are discussed as the criterion for thermodynamic miscibility. From the temperature variation of the free energy parameter, phase diagrams for both blends were obtained. 

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