1045hence increases the rigidity of the polymer.(ii) In the second explanation, the assumption is made that the compressibility of PVA in the adsorbed state is the same as in solution; i.e., no structural changes occur on adsorption. However, in this model the adsorbed PVA hinders the surface chemical reaction between the surface sites (sulfate and sulfonate end groups) and counterions (H+) due to dipole-ion interactions between alcohol segments of the PVA and the end groups of the latex. Ottewill and Vincent26 made a study of adsorption and wetting behavior of 1-alkanols of polystyrene latex particles. From the adsorption isotherm of 1-butanol on the latex particles, they reached the conclusion that the interaction occurred between hydroxyl groups on the butanol molecule and the hydrophilic sites of the surface. They also concluded that adsorption of alcohol molecules on the charged hydrophilic sites leads to desorption of the counterions from the inner part of the double layer.In Figure 6, the solid line represents the compressibility of the latex (from Figure 3) while the points are the compressibility calculated from data with the PVA-coated latex assuming that the compressibility observed is of the right order of magnitude to be explained by the elimination of the relaxation compressibility arising from the surface chemical reaction.With the present experimental evidence, it is not possible to distinguish between the two possible explanations given above.Acknowledgment. We are indebted to Dr. C. A. Young, who carried out the adsorption isotherms of various PVA samples on polystyrene latex samples, to Mr. M. J. Castle and Dr. M. C. Wilkinson of the Chemical Defense Establishment, Porton Down, Salisbury, Wiltshire, England, for determination of the glass transition temperature of the latex A and sucrose density centrifuge density measurements on various latices. Latex A was prepared by one of the authors (M.E.G.) in Bristol University, U.K. A sample of this latex was used in the present work with the kind permission of Prof. D. H. Everett. This research has been supported by the Office of Naval Research.Polystyrene, 9003-53-6; sodium styrenesulfonate-styrene copolymer, 39307-76-1; poly(viny1 acetate), Registry No. 9003-20-7.A lattice model is developed and used to study retention and selectivity in reversed-phase liquid chromatography (RPLC). The composition and the structure of the stationary phase are analyzed as a function of the chain length of the chemically bonded phase (CBP), the intrinsic chain stiffness, the surface coverage, and the nature of the mobile-phase solvent, for neat solvents and binary mixtures. The solute distribution process (retention mechanism) is investigated. Distribution constants are analyzed as a function of the above variables, the nature of the solute, and the temperature. The general behavior of the model system and the behavior of the special limiting cases of completely collapsed and fully extended CBP chains are considered, the former limiting case being particularly signifi...
A statistical thermodynamic treatment based on a lattice-fluid model is used to describe the equilibrium between a mobile fluid phase and a stationary liquid phase in chromatographic systems. General equations, applicable to gas, liquid, and supercritical fluid mobile phases, are obtained for the equilibrium composition of the stationary phase and for solute retention in fluid-liquid chromatography. These equations yield familiar retention expressions for ideal and moderately nonideal gas-liquid chromatography (GC), for traditional liquid-liquid chromatography (LC), and for reversed-phase liquid chromatography with chemically bonded stationary phases. It is shown that replacing the "poor" solvent by the "good" solvent in LC with a binary mobile phase through increasing the volume fraction of the latter is formally equivalent to replacing empty space by molecules in supercritical fluid-liquid chromatography (SFC) with a single-component mobile phase through increasing the density (occupied volume fraction) of the SF carrier. The solute capacity factor, k, in SFC is well represented by In k = In k°+ F(TR,pR), where TR and pR are the reduced temperature and reduced density of the mobile phase, F(TR,pR) (eq 82) is the mobile-phase contribution which is a quadratic function of pR and a linear function of TRl and solute carbon number (homologous solute series), and k°, the stationary-phase contribution, is the capacity factor as pR -* 0, corresponding to ideal GC. This SFC retention equation is successfully applied to the interpretation and prediction of experimental data.
The theory and mechanism for the reversed-phase liquid chromatographic separation of macromolecules was somewhat vague and controversial until recently when the Flory-Huggins theory of dilute polymer solutions was used to provide the technique with a firm theoretical foundation. As a result of this treatment, the concept of a critical mobile phase composition (Xc) has been introduced to liquid chromatography. Macromolecular solutes below Xc are completely retained, while above Xc they are rapidly eluted. Because the capacity factor of a solute is related to Xc, traditional chromatographic parameters such as theoretical plate number have little meaning. A brief summary of the history of chromatographic polymer separations that foreshadows the current theory is given. A review and an evaluation of the current mechanistic status of macromolecular chromatography are presented. Also considered is the use of adsorption theory, "small molecule" theory, and solvophobic chromatographic theory for macromolecular separations. The theory and separation mechanism are relatively straightforward for synthetic polymers but tend to be more complex and less clearcut for biological polymers.
An analysis based upon the Rouse bead−spring model and the Smoluchowski many particle diffusion equation in the free draining limit is utilized to derive an expression for the steady-state permeation rate of homopolymeric chainlike molecules passing through a narrow pore with a cross-sectional area slightly greater than that of an individual chain segment in an otherwise impenetrable barrier that separates in general two different solvent environments. The analysis is also applied to determine the steady-state permeation rate of homopolymers diffusing across a planar liquid−liquid interface formed by two immiscible solvents. The planar interface corresponds to a pore whose cross-sectional area is much larger than the mean square end to end dimensions of the polymer molecule. The key results give the permeation rate, J, as a function of the degree of polymerization, N, the individual bead diffusion coefficient(s) D i (i = 1, 2) in the different solvents and a localized pore or interfacial surface contact resistance, h. The polymer−pore permeation rate becomes J ≃ D R/N 3 where D R = D 1 D 2/(D 1 + D 2) whenever h/D R ≫ 1 and is consistent with the prediction of reptation dynamics.
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