Agustín Campos

Viscometric study on the compatibility of polymer-polymer mixtures in solution

Abstract The viscosity behaviour of mixtures formed by two uncharged polymers in dilute solution has been studied at 25°C. The ternary systems assayed, and denoted solvent (1)/ polymer (2)/ polymer (3), have in common the poly(ether sulphone) (PES) as polymer 2, and poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) as polymer 3. The intrinsic viscosity and the viscometric interaction parameters have been experimentally measured for the binary (solvent/polymer) as well as for the ternary systems, and also theoretically evaluated for the latter. The estimation of the compatibility degree of the above polymer pairs have been done by means of three criteria: (i) the sign of Δbm, according to the traditional formalism developed by Krigbaum and Wall; (ii) the sign of a new defined Δb′m; and (iii) the sign of Δ[η]m. The two last criteria are proposed in this work and are based on treating the viscosity interaction parameter and the intrinsic viscosity as excess properties by similarity with those of real solutions. Both methods provide compatibility predictions in agreement with those made with the traditional one but they are much more simple in handling the calculations. Finally, the observed compatibility behaviour follows the order: (PES+PMMA)≫(PES+PVDF)>(PES+PS), in dimethylformamide as solvent, at least in the assayed composition range.

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.

Evaluation of thermodynamic parameters for blends of polyethersulfone and poly(methyl methacrylate) or polystyrene in dimethylformamide

Liquid-liquid phase separation phenomena have been investigated for a ternary system containing two polymers and a solvent. Namely, dimethylformamide (DMF)/polyethersulfone (PES)/poly(methyl methacrylate) (PMMA) and DMF/PES/Polystyrene (PS). The composition of the three components in the two phases in equilibrium has been determined by size exclusion chromatographic (s.e.c.) analysis. The lattice-based mean-field theory, first developed by Flory and Huggins, has been modified to adequately describe these systems. In this respect, we have assumed that the parameters depend on the polymer concentration, and we have included a ternary parameter. The phase equilibrium compositions have been used as input data to solve a set of equations raised following four different approximations mainly concerned with the composition dependence of the interaction parameters. Values of the Gibbs free energy of mixing as a function of the blend composition were also evaluated and discussed in terms of the blend stability.

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.

Time-dependent monomerization of gramicidin A, enhanced by phosphatidylcholine in non-polar solvents : A high-performance liquid chromatographic and spectrofluorometric study

Abstract The usefulness of size-exclusion high-performance liquid chromatography for the study of gramicidin A dimer—monomer conformational equilibrium in non

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.

Interaction parameters in the n-undecane/butanone/poly(dimethyl siloxane) system

Abstract Intrinsic viscosities, [η], second virial coefficients, A2, preferential solvation coefficients, λ, and binary interaction potential as measured by light scattering, g12, for the system n-undecane(1)/butanone(2)/poly(dimethylsiloxane) (3) have been determined at 20.0°C. The system shows cosolvent character, as the inversion in λ and the maxima in A2 and in [η], at o 10 ⋍0.65 , seem to indicate. (g13 – sg23) and the ternary interaction potential, gT, and its derivatives on system composition, ( ∂g T ∂u 1 ) o 3 →0 and ∂g T ∂o 3 ) u 1 ,o 3 →0 , have been evaluated. Global interaction parameters, χm3, have also been evaluated and a critical analysis on the approximations usually followed for χm3 calculations is undertaken.

Mark–Houwink Parameters of Biosynthetic Poly(γ-glutamic acid) in Aqueous Solution

A combined viscosity–light scattering–gel permeation chromatography (GPC) study was carried out on bacterially produced poly(γ-glutamic acid) (PGGA). PGGA samples with weight-average molecular weights ranging from 8×104 up to 8×105 g·mol–1 dissolved in phosphate buffer at 0.13 M ionic strength were used. It was found that the Mark–Houwink relation is acceptably obeyed, giving K and a values of 1.84×10–6 dL·g–1 and 1.16, respectively. As expected, GPC analysis showed that PGGA does not follow the universal calibration plot and that deviations can not be avoided by modifying the ionic strength.

Ternary interaction parameters in n-hexane/butanone (MEK)/poly(dimethylsiloxane) (PDMS) and n-heptane/MEK/PDMS systems

Abstract Second virial coefficients, A2, intrinsic viscosities, [η], and solvation preferential coefficients, γ, for the ternary systems n-hexane, HEX, (1)/butanone, MEK, (2)/poly(dimethylsiloxane), PDMS, (3) and n-heptane, HEP, (1)/MEK (2)/PDMS (3) have been determined at 20.0°. Binary interaction parameters, g2, have also been measured by light scattering. Inversion in γ at u 2 ⋍ 0.15 in the HEX system and at u 2 ⋍ 0.22 in the HEP system takes place. The inversion points are accompanied by smooth maxima in A2 and in [η]. Both systems show a weak cosolvent character. Theoretical γs derived, according to Flory-Huggins and Flory-Prigogine-Patterson, are compared with experimental values. The evaluation of the ternary interaction potential, gT, and its dependence on system composition allow evaluation of the binary interaction potentials and their dependence on polymer concentration.