0000000000020687
AUTHOR
Iolanda Porcar
showing 26 related works from this author
Polymer-polymer interaction, in the presence of a solvent as measured by viscometry
2001
Dilute solution viscometry experiments have been carried out in five ternary polymer systems solvent(1)/polymer(2)/polymer(3). Values of the specific viscosity of polymer (3) in a ‘binary solvent’ formed by polymer(2) + solvent(1) have been used to determine the compatibility of the polymer blends. Krigbaum and Wall formalism has been used to predict compatibility which relies on an interaction parameter that depends on the concentration, weight fraction and molar mass of each polymer. To reduce the dependences and to clarify the criterion of compatibility, a parameter independent of polymer (3) composition and molar mass has been deduced. This parameter shows the same behaviour with polyme…
Solution properties of polyelectrolytes XII. Semi-quantitative approach to mixed electrostatic and hydrophobic polymer-gel interactions
1996
Abstract Aqueous size-exclusion chromatography of polyanions, where secondary effects affect the total separation mechanism, was investigated. For elution of polyelectrolytes on inorganic silica-based supports, the electrostatic polymer-gel repulsive interactions were evaluated through the values for a hypothetical repulsion layer, X e , according to the model developed by other workers. Using a similar procedure, the existence of an effective barrier defined as X e − X h is proposed for those systems in which electrostatic repulsion and hydrophobic interactions take place simultaneously as secondary mechanisms. X h can be viewed as a measure of the “enlargement” of the geometrical pore rad…
Morphology, flexural, and thermal properties of sepiolite modified epoxy resins with different curing agents
2006
A bisphenol A-based epoxy resin was modified with 5 wt% organically modified sepiolite (Pangel B40) and thermally cured using two different curing agents: an aliphatic diamine (Jeffamine D230, D230) and a cycloaliphatic diamine (3DCM). The morphology of the cured materials was established by scanning and transmission electron microscopy analysis. The thermal stability, thermo-mechanical properties, and flexural behaviour of the sepiolite-modified matrices were evaluated and compared with the corresponding neat matrix. The initial thermal decomposition temperature did not change with the addition of sepiolite. The flexural modulus of the epoxy matrix slightly increases by the incorporation o…
Size‐Exclusion Chromatography in Single and Mixed Eluents: Effects of Sorption of Solvent and Polymer Solutes on Novel TSK‐Gel Super AW Columns
2005
Abstract The novel TSK Gel Super AW column packing is based on a polymeric gel with residual hydrophobic and hydrophilic groups on the gel surface. These groups can act as active sites making the chromatographic support compatible both with polar and apolar eluents. This interesting property allows the elution of systems of very different polarities but also induces binary polymer–gel, polymer–solvent, and solvent–gel enthalpic interactions that lead to a mixture of separation mechanisms: repulsion, partition, or adsorption besides the main size‐exclusion chromatography (SEC) mechanism. For this reason, the elution behaviour of many and diverse polymer/solvent systems has been studied in th…
Macromolecules in ordered media. 6. Effect of the phospholipidic bilayer composition on poly (2-vinyl pyridine) - liposome association
1997
The intrinsic fluorescence emission of poly (2-vinyl pyridine) has been exploited in order to gain insight into the nature of the interaction with artificial membranes. In this contribution, the study has been focused on the effect of the phospholipid bilayer composition on the association to the polymer. Fluorescence data have been converted into association isotherms and then analyzed in terms of both binding and partition models. Results show that the association is enhanced by the presence of negative charged phospholipid as a constituent of the liposomal membrane. The strong surface density dependence of the polymer-liposome association indicatesthe predominantly electrostatic nature o…
Porous fractal gels: secondary effects in SEC
1992
Abstract The fractal nature of porous silica gels, Spherosil XOA 200 and of a Lichrospher mixture, has been tested through size exclusion chromatography of polystyrene in pure and mixed eluents. Fractal parameters, D f and L , depend on eluent with D f values close to 2.0 for Spherosil and higher than 2.0 for Lichrospher. D f and L changes with eluent have been related to secondary separation effects and partition and adsorption contributions have been evaluated.
The Fractal Approach to Secondary Mechanisms in SEC
2007
Abstract Size‐exclusion chromatography (SEC) is one of the most used experimental techniques to characterize polymers in solution; it has been applied to interpret the elution behaviour of many polymer‐solvent systems in five types of column packings. The experimental data have revealed that the classical universal calibration is not accomplished. Deviations from a unique curve are a consequence of two effects: entropic (exclusion by size) and enthalpic (binary and ternary interactions between solvent, polymer, and gel), which results in secondary mechanisms accompanying the main “ideal” SEC separation mechanism. Therefore, three approaches of building a calibration curve have been compared…
The fractal calibration method applied to the characterization of polymers in solvent mixtures and in mixed gel packings by SEC.
2007
The size-exclusion chromatographic (SEC) behaviour of different solvent/polymer systems in three packing sets has been analysed from fractal considerations. The three-column sets studied are specifically formed by: (i) 'pure' micro-styragel, (ii) 'mixed' TSK Gel H(HR + XL + HR) and (iii) mixed TSK Gel H(XL + HR + XL). The experimental data reveals that in most of the systems assayed the classical universal calibration (UC) is not fulfilled, denoting the existence of secondary effects accompanying the main SEC mechanism. In order to obtain an accurate characterization of different polymers eluted in solvent mixtures and/or mixed packings, the use of a reliable and trusted calibration curve i…
Preferential solvation of poly(methyl methacrylate) and a bisphenol A diglycidyl ether by size-exclusion chromatography
2004
The preferential adsorption coefficient, lambda, of poly(methyl methacrylate), PMMA, in solutions formed by an epoxy resin in tetrahydrofuran (THF), was studied by size-exclusion chromatography (SEC). Only PMMA of lowest molar mass was preferentially solvated by epoxy but at low concentrations of epoxy in the mixture. At higher epoxy content PMMA was preferentially solvated by THF. A simultaneous and competitive solvation between the specific interactions PMMA-epoxy and the self association of epoxy at high concentrations would be the responsible of this inversion point. The more compacted coil of PMMA of higher molecular weights in solution could explain the lack of interaction of these po…
Viscometric study of mixtures of neutral and charged polymers in aqueous solution
1997
The viscosity behaviour of aqueous mixtures formed by a polyelectrolyte (A) and a neutral polymer (B) such as polystyrene sulfonate (PSS)-polyvinylpyrrolidone (PVP) and polylysine (PLL)-PVP has been studied at 25°C. The intrinsic viscosity and viscosity interaction parameter of each polymer in water have been determined and have served us to estimate the compatibility of the different mixtures according to two different methodologies: (i) mixtures of two polymers in water as solvent and (ii) mixtures of either polymer A OFB in a solvent formed by either polymer B or A in water ("polymer solvent method"). By comparing the experimental and theoretical viscosity data it is clearly seen that: m…
Interaction of quinine with negatively charged lipid vesicles studied by fluorescence spectroscopy Influence of the pH
1997
Abstract The interaction of quinine with dimyristoylphosphatidic acid (DMPA) and dimyristoylphosphatidyl glycerol (DMPG) small unilamellar vesicles in the gel phase was studied by steady-state fluorescence spectroscopy at pHs 7, 6, 5 and 4 and 20°C. In aqueous solution, with excitation at 335 nm, the emission fluorescence spectrum of quinine varied with pH reflecting the occurrence of different charged species of the drug. In all cases, the emission maximum centered at 383 or 443 nm shifted to lower wavelength in the presence of vesicles. This indicates that the membrane-bound state quinine is in an environment of low polarity. Drug monocationic species were deeply buried in DMPG relative t…
Interaction of Quinine with Model Lipid Membranes of Different Compositions
2002
The binding of a drug such as Quinine with neutral and negatively charged small unilamellar lipid vesicles at pH 7 and 37 degrees C was investigated. Changes in the fluorescence properties of the drug after association with the liposomes were used to obtain binding isotherms over a range of phospholipid compositions at different ionic strengths. Under such conditions, the association was strongly enhanced by the negative net charge of the bilayer but diminished by the increasing presence of electrolytes in the aqueous media. Binding data were analyzed in terms of a surface partition equilibrium without and after correcting for electrostatic effects by means of the Gouy-Chapman theory. The i…
Macromolecules in ordered media: 4. Poly(2-vinyl pyridine)-liposome association induced by electrostatic interactions
1997
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 …
Binding of basic amphipathic peptides to neutral phospholipid membranes: a thermodynamic study applied to dansyl-labeled melittin and substance P ana…
1997
A thermodynamic approach is proposed to quantitatively analyze the binding isotherms of peptides to model membranes as a function of one adjustable parameter, the actual peptide charge in solution z(p)+. The main features of this approach are a theoretical expression for the partition coefficient calculated from the molar free energies of the peptide in the aqueous and lipid phases, an equation proposed by S. Stankowski [(1991) Biophysical Journal, Vol. 60, p. 341] to evaluate the activity coefficient of the peptide in the lipid phase, and the Debye-Huckel equation that quantifies the activity coefficient of the peptide in the aqueous phase. To assess the validity of this approach we have s…
Modelling the influence of nanoparticles in the phase behaviour of an epoxy/polystyrene mixture
2007
Abstract The cloud point temperatures of four series of epoxy/polystyrene blends have been experimentally determined as a function of polymer mass and system composition. The phase diagrams show an UCST behaviour, increasing incompatibility as the molar mass increases. The Flory–Huggins theory with a concentration-dependent interaction parameter has been developed to study the compatibility of two polymers in presence of spherical nanoparticles. This theory has been first compared with the experimental cloud point curve in absence of nanoparticles, and secondly it has been used to predict the thermodynamic behaviour in presence of different volume fraction of nanoparticles. Nanoparticles co…
Macromolecules in ordered media: 7. Influence of ionic strength and bilayer composition on the association of polyelectrolytes to mixed liposomes
1997
The effect of both the phospholipid composition of the bilayer and the ionic strength of the medium on the association between poly(2-vinyl pyridine) and mixed liposomes based on dimyristoyl phosphatidic acid and dimyristoyl phosphatidil choline was investigated using fluorescence spectroscopy. Intensity changes upon addition of vesicles have allowed us to estimate the extent of the association and data have been processed as association isotherms. We found that the association is enhanced by increasing both the ionic strength and the anionic phospholipid fraction. However, whereas the negative net charge of the bilayer strongly enhances the interaction, the presence of more and more electr…
Miscibility of Blends of Biodegradable Polymers and Copolymers with Different Plasticizers
2008
Miscibility between components of different plasticizer(A)/solvent(B)/biodegradable polymer(C) ternary systems with H-bonding has been compared. Systems were formed by two H-donor phenolic plasticizers, 4-nonylphenol (NP) and 4:4'-dihydroxydiphenylmethane (BPF); an H-acceptor solvent, epichlorohydrin (ECH); and H-acceptor poly(3-hydroxybutyrate) (PHB) or poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBHV) copolymers. Blend miscibility is the result of the balance of three competitive H-bondings: plasticizer self-association (AA), plasticizer-solvent (AB) and plasticizer-polymer (AC) interassociations. The strength and extent of such specific interactions have been experimentally monito…
Interactions of quinine with polyacrylic and poly-L-glutamic acids in aqueous solutions
2004
Abstract Drug-loaded polymers provide an attractive form for controlled drug delivery systems. A proper knowledge of polymer–drug interactions can aid in the designing of polymers for various drug-delivery applications. In this paper we have investigated the interaction of a drug such as quinine, with synthetic macromolecules such as poly(acrylic acid), PAA, and poly(L-glutamic acid), PGA, at pH 7 and 37 °C by fluorescence spectroscopy and viscometry. The analysis of the binding isotherms revealed that the association process is positive cooperative up to a threshold concentration and then it is negative. In addition, the thermodynamic parameters vary along the isotherm. Results also sugges…
Macromolecules in ordered media: 5. Poly(4-vinyl pyridine)—liposome association induced by electrostatic interactions
1997
Abstract The association of water-soluble vinyl polymers to dimyristoyl phosphatidic acid unilamellar vesicles as a function of pH, temperature and salt content using steady-state fluorescence and viscometry has been investigated. Poly(4-vinyl pyridine) fluorescence data were converted to association isotherms and discussed in terms of binding and partition models. The results of this report support previous suggestions: (1) in the case of polyions the inclusion of the activity coefficient in both models is essential; (2) the parameters calculated using the two different theoretical approaches can be directly compared by the relating equation proposed for us. Finally, the excellent agreemen…
Solution properties of polyelectrolytes
1993
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 …
Macromolecules in ordered media VIII. High-performance size-exclusion chromatography as a technique for characterizing the interaction between polyan…
1997
Abstract The association of polyanions with liposomes based on dimyristoyl phosphatidyl choline and stearylamine at a ratio of 50:50 was investigated in terms of the binding model and, to a lesser extent, of the partition model. Aqueous size-exclusion chromatography has been proposed as a major technique for monitoring the interactions between liposomes and polyelectrolytes and the results were compared with those obtained by fluorescence spectroscopy. Quantitatively, the extent of the association follows the order: Sodium poly(styrene sulfonate) ( K A = 10 000 M −1 ), poly (acrylic acid) ( K A = 2000 M −1 ) and poly ( l -glutamic acid) ( K A = 700 M −1 ). Also, the effect of the ionic stre…
Investigation of compatibility of a dicyanate ester monomer and polysulfone by size-exclusion chromatography and viscometry
2003
The influence of solvent on the compatibility behaviour of Arocy B10, a cyanate ester monomer, and polysulfone (PSF) was investigated by means of dilute solution viscometry and of the preferential solvation parameter at 25 °C. The ternary systems under study are: tetrahydrofuran/Arocy B10/polysulfone (PSF), N,N-dimethylformamide/Arocy B10/PSF and dichloromethane/Arocy B10/PSF. Values of the specific viscosity of PSF in a ‘binary solvent’ formed by Arocy B10 + solvent have been used to determine the compatibility of the polymer blend Arocy B10/PSF. An interaction parameter Δb that depends on concentration has been determined. The preferential solvation parameter was measured by size-exclusio…
Macromolecules in ordered media. II. A fluorescence study of the polymer-liposome association
1995
The interactions of poly (4-vinyl pyridine) with dimyristoylphosphatidic acid-based liposomes were studied in heterogeneous solution systems. The polymer was dispersed in aqueous buffer solutions of small unilamellar vesicles and after a suitable period of incubation to raise the equilibrium, the experiments has been conducted as a function of polymer concentration and temperature. According to the measurements of the steady-state fluorescence spectra, changes in the intensities as well as shifts in the emission peak wavelength, has served as raw data to accounting for the polymer-vesicle interactions. Quantitative evaluation of the interaction has been done using a simple associating model…
Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography.
2002
Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in …
Solution Properties of Poly-Electrolytes. XI. Adsorption Effects in Aqueous Size-Exclusion Chromatog-Raphy of Polyanions
1994
Abstract Elution profiles of a series of polymer standards such as sodium poly(styrene sulphonate), poly(acrylic acid) and poly(L-glutamic acid) have been obtained from size-exclusion chromatography experiments using separately two types of hydrophilic supports. A variety of mobile phase compositions have been performed to enhance adsorption effects in order to study how this phenomenon can affect to the chromatographic separation mechanism of polyanions. Distribution coefficient values, in general greater than unity, have served to quantify the adsorption effect, as well as to analyze their dependence on eluent ionic strength, on the ionic groups of the support and on the chemical nature a…
Macromolecules in ordered media III. A fluorescence study on the association of poly-2-vinylpyridine with a phospholipid bilayer
2007
Association of low molecular weight poly-2-vinylpyridine taken as a polycation model with unilamellar vesicles based on dimirystoylphosphatidic acid has been experimentally investigated by means of fluorescence energy transfer experiments. The conventional profiles for the binding isotherms were obtained, confirming strong deviations from the ideality of these complex fluid composites. Two approaches, named binding and partitioning equilibrium, respectively, were used to obtain the association constant, K A; the number of phospholipids that form a binding site, N; the partition coefficient, Λ; the activity coefficient, γ; and the effective charge, v. Analysis of these parameters as a functi…