Solute polydispersity, effect

A ternary system consisting of two polymer species of the same kind having different molecular weights and a solvent is the simplest case of polydisperse polymer solutions. Therefore, it is a prototype for investigating polydispersity effects on polymer solution properties. In 1978, Abe and Flory [74] studied theoretically the phase behavior in ternary solutions of rodlike polymers using the Flory lattice theory [3], Subsequently, ternary phase diagrams have been measured for several stiff-chain polymer solution systems, and work [6,17] has been done to improve the Abe-Flory theory. 

Rebar VA, Santore MM. Molecular weight effects and the sequential dynamic nature of poly(ethyleneoxide) adsorption on silica from polydisperse aqueous solution. Macromolecules 1996 29 6273—6283. 

Demixtion is one of the clearest manifestations of the attractive forces between molecules of a solute, but it is sensitive to polydispersion effects. Therefore, demixtion is studied experimentally by using samples which are as monodis-perse as possible. 

In this paper, we review continuous thermodynamics as applied to copolymer systems. Special attention is focused on liquid-liquid equilibria and thermodynamic stability. Equilibria in solutions of random copolymers, blends of random copolymers with homo- or copolymers, and also the high pressure phase equihbrium in the mixture of copoly(ethene vinylacetate) with its monomers are also discussed. A special examination of polydispersity effects in solutions with block copolymers is made. Thus, the paper reviews in a comprehensive way how to build up continuous thermodynamics with multivariate distribution functions and how to derive relations necessary for solving special problems. Some short remarks on possible future prospects will round up the paper. 

QLS has been used routinely to determine the Z-average translational diffusion coefficient and the corresponding hydrodynamic radius of macromolecules in solutions and of colloidal suspensions (11,12) and also to characterize the polydispersity effects the method of cumulants (13). 

It is strongly suggested to further investigate the solution properties of PDA both in their "yellow and their "blue state. The molecular weight dependence of the hydrodynamic properties should be able to differentiate between possible chain conformations (e.g. T) - M, 0.5 < a < 1 for random coils, a 2 for rods) polydispersity effects should, however, be properly taken into account. Similarly orientation in an electric field (Kerr-effect) could be used. 

The counterions associated with an ionic amphiphile may have a pronounced effect on micellar properties. In extreme cases, for example with amphiphilic drugs such as mepyramine and brompheniramine maleate containing pyridine rings, a proton transfer interaction may occur between maleate counterions and the nitrogen of the pyridine ring [115]. A consequence of this interaction is a very polydisperse micellar solution with no clear CMC [116] (see Chapter 4). 

HAR Haruki, M., Nakanishi, K., Mano, S., Kihara, S.-L, and Takishima, S., Effect of molecular weight distribution on the liquid-liquid phase separation behavior of polydispersed polyethylene solutions at high temperatures. Fluid Phase Equii., 305, 152, 2011. 

However, in subsequent studies [23-25,88-90] it was demonstrated that in reality the particle deposition is not a purely geometric effect, and the maximum surface coverage depends on several parameters, such as transport of particles to the surface, external forces, particle-surface and particle-particle interactions such as repulsive electrostatic forces [25], polydispersity of the particles [89], and ionic strength of the colloidal solution [23,88,90]. Using different kinds of particles and substrates, values of the maximum surface coverage varied by as much as a factor of 10 between the different studies. 

The different location of polar and amphiphilic molecules within water-containing reversed micelles is depicted in Figure 6. Polar solutes, by increasing the micellar core matter of spherical micelles, induce an increase in the micellar radius, while amphiphilic molecules, being preferentially solubihzed in the water/surfactant interface and consequently increasing the interfacial surface, lead to a decrease in the miceUar radius [49,136,137], These effects can easily be embodied in Eqs. (3) and (4), aUowing a quantitative evaluation of the mean micellar radius and number density of reversed miceUes in the presence of polar and amphiphilic solubilizates. Moreover it must be pointed out that, as a function of the specific distribution law of the solubihzate molecules and on a time scale shorter than that of the material exchange process, the system appears polydisperse and composed of empty and differently occupied reversed miceUes [136],... 

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