Polymers solvation solution theories

The randomly occupied lattice model of a polymer solution used in the Rory-Huggins theory is not a good model of a real polymer solution, particularly at low concentration. In reality, such a solution must consist of regions of pure solvent interspersed with locally concentrated domains of solvated polymer. 

In general, to explain the observed cosolvent effects, the preferential adsorption phenomena have been invoked. Flowever few topics in the physical chemistry of polymers have evoked so many theories but so little consensus as preferential adsorption. When a polymer is dissolved in a binary solvent mixture, usually one of the solvents preferentially solvates the polymer. This solvent will then be found in a greater proportion in the proximities of the macromolecule with respect to the bulk solution composition. This variation of the solvent composition can cause interesting phenomena such as cosolvency as was discussed before, [11, 91, 92] non - cosolvency [93, 94], and some times variation of the unperturbed polymer dimensions [95,96]... 

In this chapter we will mostly focus on the application of molecular dynamics simulation technique to understand solvation process in polymers. The organization of this chapter is as follow. In the first few sections the thermodynamics and statistical mechanics of solvation are introduced. In this regards, Flory s theory of polymer solutions has been compared with the classical solution methods for interpretation of experimental data. Very dilute solution of gases in polymers and the methods of calculation of chemical potentials, and hence calculation of Henry s law constants and sorption isotherms of gases in polymers are discussed in Section 11.6.1. The solution of polymers in solvents, solvent effect on equilibrium and dynamics of polymer-size change in solutions, and the solvation structures are described, with the main emphasis on molecular dynamics simulation method to obtain understanding of solvation of nonpolar polymers in nonpolar solvents and that of polar polymers in polar solvents, in Section 11.6.2. Finally, the dynamics of solvation with a short review of the experimental, theoretical, and simulation methods are explained in Section 11.7. 

Increased moisture can plasticize a polymer matrix. Water acts not only as a solvent for small solutes but as an agent that increases the free volume of polymer molecules and their degree of segmental motion (i.e., water is differentially solvated and mobilizes parts of the heterologous structure of protein and polysaccharide polymers). When polymers, or segments within them, are given more freedom of movement, then other diffusion-based phenomena might occur more readily. Chemical reactions should not necessarily be expected to be affected by increased free volume of the polymer, and a review of the literature yields little support for this theory for most chemical reactions. Instead, some of the increased reaction rates that have been attributed to plasticization are instead the result of increased solvation. 

Flocculation has also been observed when the diluent of the dispersion is a good solvent for the chains constituting the steric barrier. This is observed when free polymer, even when it is identical to that constituting the steric barrier, is dissolved in the diluent of the dispersion [3.77]. The magnitude of flocculation is a function of both the molecular mass and the concentration of the added polymer. The depletion flocculation theory suggests that this phenomenon is related primarily to the perturbation of the free polymer chains in solution rather than those in the solvated sheath [3.78]. 

When a size-exclusion chromatograph is calibrated correctly, one can know the molecular weight of a polymer just based on the time it takes to pass, or elute through the column. From Fox and Flory s theory of solution viscosity one can learn that the size of a solvated macromolecular coil is directly correlated with its solution viscosity. The correlation is ... 

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