Vicente Soria

Extension of the Flory-Huggins theory to study incompatible polymer blends in solution from phase separation data

Abstract A method is presented to evaluate the Koningsveld g -functions for quasi-ternary polymer solutions and blends, involving binary and ternary interactions. A robust set of 12 equations derived from the Flory—Huggins lattice theory, dealing with liquid—liquid phase separation conditions, have been solved using as input data the experimental volume fractions of each component in each coexisting phase. These values were found by means of a liquid microextraction procedure followed by size-exclusion chromatography analysis. Several approximations are proposed and discussed in order to select the best option to predict thermodynamic properties of binary polymer blends and blends in solution. The dimethylformamide/poly(vinylidene fluoride)/polystyrene ternary solution was chosen to test the validity of our proposal. In general, the analytical form of the g -function is adequately described by a second order polynomial, the inclusion of the ternary interaction parameter also being recommended. From the values of the PVDF/PS interaction function it can be inferred that this blend behaves as slightly incompatible under environmental conditions, in clear agreement with data previously reported. In contrast, the incompatibility is suppressed when a low molar mass component, such as dimethylformamide, is added, reaching the semidilute regime (total polymer volume fraction p ≈ 0.35). Values of the Gibbs free-energy of mixing as a function of the blend composition were also evaluated for both ternary solution and dry blend and discussed in terms of their stability.

Polymer-polymer interaction parameters in solvent/polymer/polymer ternary systems

Abstract Empirical equations defining the relationships between b23 and χ23 interaction parameters for the ternary systems toluene (1)/poly(dimethylsiloxane), PDMS, (2)/polystyrene, PS, (3) and benzene (1)/PDMS(2)/PS(3) have been determined. The dependences of both interaction parameters on the mean molecular weights of the macromolecular components have also been studied. A single dependence of b23 (or χ23) upon the mean molecular weight is found when both polymeric components have intermediate to high molecular weights. However, that single dependence is not found when the molecular size of polymer (2) is low.

On the thermodynamic treatment of poly(vinylidene fluoride)/polystyrene blend under liquid—liquid phase separation conditions

Abstract This paper deals with experimental and theoretical investigations on the compatibility of binary of polymer blends in solution. The experimental phase boundary of a crystalline polymer such as poly(vinylidene fluoride) with polystyrene (an amorphous polymer) in dimethylformamide as solvent has been determined by size-exclusion chromatography at 25°C. The composition of the coexisting phases has been used to calculate interaction parameters by means of the Flory—Huggins-type function for the free energy of mixing, including composition dependence of the polymer-polymer interaction parameter and a first correction term denoted as ternary interaction parameter. The calculation of these parameters involves the solution of a system of equations that should be equal to the number of unknown parameters. Diverse approximations have been proposed in order to reduce the number of equations to be solved; they are mainly concerned with the composition dependence of both binary polymer-polymer and ternary interaction parameters and of their derivatives.

Macromolecules in ordered media: 1. Interfacial interactions between a cationic polymer and oppositely charged liposomes

Abstract The incorporation of a cationic polymer, such as poly(4-vinylpyridine), to the outer leaflet of negatively charged phospholipid vesicles of dimyristoylphosphatidic acid has been investigated by viscometry and intrinsic fluorescence. Viscosity changes of dilute solutions follow the size of the polymer and the polymer-liposome complex. Variations in the emission spectrum of poly(4-vinylpyridine) upon the addition of lipid vesicles under different conditions give the amount of polymer bound per mole of accessible lipid. These experimental results have been interpreted by means of the Gouy-Chapman formalism, which calculates the effective number of charges per polymer chain at the interface. The size of the adsorbed polyion has been computed from a discrete charge virial expansion that takes into account the mobility of charged groups at the interface.

Solution properties of polyelectrolytes. VIII: A comparative study of the elution behaviour on two organic-based packings

Abstract Aqueous size-exclusion chromatography was used to analyse the elution behaviour of several standard ionic polymers, including poly( l -glutamic acid), sodium poly(styrene sulphonate) and poly(acrylic acid), different in nature and chain flexibility, as a function of the pH and ionic strength of the eluent. Two organic-based hydrophilic packings, Spherogel TSK PW4000 and Ultrahydrogel 250, were tested in order to select the optimal conditions of macromolecular separation, and the results obtained for each column were compared. A set of calibration graphs for the above polyions as a function of eluent pH and ionic strength were obtained and compared with those obtained for uncharged standards (dextran and polyethylene oxide, PEO) under the same experimental conditions. The divergence between both charged and uncharged plots served to interpret the separation mechanisms for the polyions, other than pure size exclusion. Deviations from ideal elution behaviour have been attributed to ion-exclusion and hydr ophobic effects, as a consequence of the repulsive or attractive interactions between the ionizable groups of the polyelectrolyte and the residual surface charge of the support.

Macromolecules in ordered media: 4. Poly(2-vinyl pyridine)-liposome association induced by electrostatic interactions

Abstract We have investigated the interaction between vesicles based on dimyristoyl phosphatidic acid (DMPA) and a polymer, such as poly(2-vinyl pyridine) (P2VPy), on the basis of both partition and binding models. The resulting association curves are non monotonous being three regions clearly evidenced. The electrostatic and steric origin of the attractive or repulsive interactions are analyzed as a function of pH, ionic strength and temperature using the fluorescence spectroscopy technique. We emphasize the importance of differentiating the ideal definition of the binding constant from the theoretically evaluated including the activity coefficient, γ, to take into account shifts from the ideality of the polymer in both aqueous and lipidic domains. Furthermore, we propose an equation relating both models that predicts fairly well the experimental data.

Solution properties of polyelectrolytes: X. Influence of ionic strength on the electrostatic secondary effects in aqueous size-exclusion chromatography☆

Abstract The retention behaviour of polyelectrolytes in aqueous size-exclusion chromatography (SEC), where electrostatic repulsion is the main secondary effect affecting to the separation mechanism, was investigated. A theoretical treatment was developed in order to establish the influence of the mobile phase ionic strength on calibration graphs, often used for the characterization of polyions by SEC. A master equation, derived in closed form, involving two terms related to the net charge of polyion and the residual surface charge on the gel packing, was derived. The formalism provides the basis for a more detailed analysis of chromatographic retention data in electrostatic interaction systems. Moreover, the introduction of some approximations in the original equation served to obtain an equivalent expression that is easier to use, and in which the functionality with respect to the ionic strength, I, remains unaltered. Reported data on the elution of sodium polystyrene sulphonate and poly( l -glutamic acid) from both organic and silica-based packings were used to test the goodness of the predictions carried out with the above-mentioned equations.

Solution properties of polyelectrolytes : IV. Use of a new hydrophilic size-exclusion chromatographic packing for the separation of anionic and cationic polyions

Abstract The chromatographic behaviour of sodium polystyrenesulphonate in Ultra-hydrogel aqueous size-exclusion chromatographic packings was analysed under different experimental conditions. Three types of mobile phases (salt-free water, sodium nitrate solution and buffers of different pH) were investigated in order to characterize the elution mechanisms and to optimize the separation. Several parameters, such as sample concentration, injection volume, eluent pH and ionic strength were considered. Finally, a “universal” calibration graph was obtained under simple, mild optimized conditions of the mobile phase (0.2 M acetate buffer, pH 4.0), which is congruent for both polyanions and polycations and also for uncharged polymers.

Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)

The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by a dilute probe polymer in the presence of a matrix polymer and a small molecule solvent.

Solution properties of polyelectrolytes: VII. Non-ideal mechanisms in size-exclusion chromatography of synthetic polyions, peptides and proteins

Abstract Chromatographic data for sodium polystyrene sulphonate were obtained on both silica- and polymer-based size-exclusion supports using mobile phases of various pH and ionic strength. Deviations of the elution volume were observed towards both lower and higher values relative to the reference calibration graph obtained with uncharged standards. An empirical correlation is proposed in order to account for all the secondary effects observed. The general applicability of this correlation was further tested for chromatographic data obtained for a series of peptides and proteins on a silica-based support under very different eluent conditions. Deviations from ideal elution behaviour such as ion-exclusion and hydrophobic effects were analysed in the light of this approach.