18 research outputs found
Estimation of the Molecular Weight Distribution of Linear Homopolymer Blends from Linear Viscoelasticity for Bimodal and High Polydisperse Samples
This work is concerned with the approximate solution of the problem generated by the integral of first kind relating the shear relaxation modulus of entangled, linear and flexible homopolymer blends and the molecular weight distribution (MWD). Procedures are proposed to estimate the density distribution function (DDF) of the MWD from numerical solutions of the theoretical model composed by the double reptation mixing rule and a law for the relaxation time of chains in polydisperse matrixes. One procedure uses the expansion of the DDF through orthogonal polynomial functions. This expansion is formulated for two cases: a) Hermite polynomials associated with the normal-DDF and b) Laguerre polynomials associated with the gamma-DDF. The other procedure uses the mean value theorem of continuum functions, which turns out the integral problem into a differential form. Calculations are carried out with dynamic rheometric data of linear viscoelasticity for samples of polydimethylsiloxane, polypropylene and polybutadiene. High values of polydispersity are considered. The predictions of the DDF through these procedures compare well with experimental data of size exclusion chromatography (SEC).Fil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
Modeling Melt Spinning with Stress Induced Crystallization at High Take Up Velocities: Numerical Results for the PET Melt
The purpose of this work is to present a 2-D thermo-rheological model for high take up velocities that can predict numerically in the filament domain, the axial velocity profile together with the radial and axial resolutions of stresses, temperature and degree of crystallization. The rheology of the filament is described through a constitutive equation that results from the combination of the Phan-Thien and Tanner viscoelastic model for the amorphous phase and the kinetic model of the rigid dumbbell for the crystalline phase immersed in the melt. The model is thus able to predict the thermal and mechanical coupling between both phases through the degree of transformation (relative degree of crystallization) when the balances of mass, momentum and energy are invoked. The effects of stress induced crystallization, viscoelasticity, friction of cooling air, filament inertia, gravity and surface tension are all considered together with the temperature dependency of polymer and cooling air thermo-physical properties. The rate of crystallization is evaluated through the nonisothermal Avrami-Nakamura equation. Also, the relaxation times of both phases are function of temperature and degree of transformation. Numerical predictions of the model compare well with experimental data reported in the literature for a PET melt at a take up velocity of 5490 m/min. Also, consistently with experimental observations reported in the literature, the “skin-core” structure is predicted. It is relevant to indicate that the model analyzed here can be evaluated from low to high take up velocities, and when the degree of crystallization becomes negligible, the one-phase model is recovered continuously.Fil: Ottone, Mariel Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
Computational Spinning Model to Study Different Expressions Proposed in the Literature for the Elongational Viscosity Evaluation from Spinning Experimental Data
The relation between isothermal elongational flow and other flow kinematics, like shear flow, was of interest since the early stages of rheometry. The main seeking purpose was precisely to achieve the evaluation of the elongational viscosity as a function of elongational rate through other simpler kinematics attained easily in experimental programs and commercial rheometers. At present, it is known that this target is not possible. It is also clear that experimental data of the steady elongational viscosity of viscoelastic melts at different temperatures are quite difficult to obtain. In this sense, various techniques for determining the elongational properties of these materials were developed; the apparatuses involved are considered expensive, difficult to operate and unsuitable for most types of materials, especially for those having a low viscosity. A technique widely used at present dealing with a variety of polymer melts is the isothermal fiber spinning process in its well-known version designated Rheotens. This apparatus presents a challenging problem, which consists in translating measurements of the spinning flow kinematics and filament forces into those variables pertaining to pure elongation flow within the rheometric framework. According to what has been reported in the literature, different research groups have studied this difficult problem and proposed approximate solutions for this purpose. In the present work we use a computational model of isothermal melt spinning to study the different accuracies obtained with expressions suggested in previous works to evaluate the elongational viscosity from spinning experimental data. Some physical aspects concerning the requirements to attain appropriate experimental conditions are provided, mainly those concerning the description of different zones present in the spinning kinematics.Fil: Ottone, Mariel Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
Global properties and propensity to dimerization of the amyloid-beta (12-28) peptide fragment through the modeling of its monomer and dimer diffusion coefficients and electrophoretic mobilities
Neuronal activity loss may be due to toxicity caused mainly by amyloid-beta (1–40) and (1–42) peptides forming soluble oligomers. Here the amyloid-beta (12–28) peptide fragment (monomer) and its dimer are characterized at low pH through the modeling of their diffusion coefficients and effective electrophoretic mobilities. Translational diffusion coefficient experimental values of monomer and dimer analogs of this peptide fragment and monomer and dimer mixtures at thermodynamic equilibrium are used as reported in the literature for different monomer initial concentrations. The resulting electrokinetic and hydrodynamic global properties are employed to evaluate the amyloid-beta (12–28) peptide fragment propensity to dimerization through a thermodynamic theoretical framework. Therefore equilibrium constants are considered at pH 2.9 to elucidate one of the amyloidogenic mechanisms involving the central hydrophobic region LVFFA of the peptide spanning residues 17–21 associated with phenylalanine at positions 19 and 20 in the amino acid sequence of amyloid-beta peptides. An analysis demonstrating that peptide aggregation is a concentration-dependent process is provided, where both pair and intraparticle charge regulation phenomena become relevant. It is shown that the modeling of the effective electrophoretic mobility of the amyloid-beta (12–28) peptide fragment is crucial to understand the effect of hydrophobic region LVFFA in the amyloidogenic process.Fil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Piaggio, María. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentin
Computational Model for Non-Isothermal Melt Spinning Flows: The Low Take Up Velocity Range
This work shows the interrelation between non-isothermal melt spinning flows and the isothermal extensional flow described through rheometry. This analysis uses the iterative numerical algorithm presented by Ottone and Deiber for non-isothermal melt spinning flows in the low take up velocity range. The results obtained for two take up velocities (1500 and 2500 m/min) are then shown in the extensional rheometric map composed by the lines of the steady state rheometric extensional viscosity as function of the extensional rate at different parametric temperatures. Then the search of scaling functions that allows one the formulation of master curves relating both flows is analyzed and discussed.Fil: Ottone, Mariel Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
Rheokinetic Model to Characterize the Maturation Process of Gelatin Solutions under Shear Flow
The characterization of maturing gelatin solutions in shear flow is required for an appropriate formulation of food products. Under static conditions, the maturation process of gelatin solutions may be described through a basic structural parameter evolving to the percolation value (gel point). Within the rheological framework, two asymptotic viscosities are well identified for the maturing process of gelatin solutions at the limit zero shear rate. One involves the initial solution viscosity that may be associated with the null structural parameter (the microstructure is not formed yet). The other is the percolation zero shear rate viscosity (assuming an infinite value when approaching the gel time) and corresponds to the maximum value of the structural parameter. Under flow, thixotropic theories combined with the knowledge of suspension rheology allow one to convert directly experimental data obtained as shear stress versus time for a given shear rate into the time evolution of the structural parameter. Consequently rheometric experimental data available places the search for a rheokinetic model of the structural parameter. Here, different expressions for this model are investigated, mainly those involving both the rates of structure breakdown and buildup, where the average cluster size is affected by the shear rate. The rate equation thus obtained may be then applied to arbitrary shear rate histories. Numerical results of the rheokinetic model proposed in this work fit well experimental rheometric data obtained in shear flow for the maturing of different gelatin solutions. Experimental data acquired in this work are presented and discussed in relation to those reported previously in the literature.Fil: Ottone, Mariel Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
Global chain properties of an all L-alpha-eicosapeptide with a secondary alpha -helix and its all retro D-inverso-alpha-eicosapeptide estimated through the modeling of their CZE determined electrophoretic mobilities
Several global chain properties of relatively long peptides composed of 20 amino acid residues are estimated through the modeling of their experimental effective electrophoretic mobilities determined by CZE for 2 < pH < 6. In this regard, an all L-alpha-eicosapeptide, including a secondary alpha-helix (Peptide 1) and its all retro D-inverso-alpha-eicosapeptide (Peptide 2), are considered. Despite Peptides 1 and 2 are isomeric chains, they do not present similar global conformations in the whole range of pH studied. These peptides may also differ in the quality of BGE components chain interactions depending on the pH value. Three Peptide 1 fragments (Peptides 3, 4, and 5) are also analyzed in this framework with the following purposes: (i) visualization of the effects of initial and final strands at each side of the alpha-helix on the global chain conformations of Peptide 1 at different pHs and (ii) analysis of global chain conformations of Peptides 1 and 2, and Peptide 1 fragments in relation to their pI values. Also, the peptidemaximum andminimum hydrations predicted by the model, compatible with experimental effective electrophoretic mobilities at different pHs, are quantified and discussed, and needs for further research concerning chain hydration are proposed. It is shown that CZE is a useful analytical tool for peptidomimetic designs and purposes.Fil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Piaggio, María Virginia. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentin
Effect of Background Electrolyte on the Estimation of Protein Hydrodynamic Radius and Net Charge through Capillary Zone Electrophoresis
Two physicochemical models are proposed for the estimation of both hydrodynamic radius and net charge of a protein when the capillary zone electrophoretic mobility at a given protocol, the set of pK of charged amino acids, and basic data from Protein Data Bank are available. These models also provide a rationale to interpret appropriately the effects of solvent properties on protein hydrodynamic radius and net charge. To illustrate the numerical predictions of these models, experimental data of electrophoretic mobility available in the literature for well-defined protocols are used. Five proteins are considered: lysozyme, staphylococcal nuclease, human carbonic anhydrase, bovine carbonic anhydrase, and human serum albumin. Numerical predictions of protein net charges through these models compare well with the results reported in the literature, including those found asymptotically through protein charge ladder techniques. Model calculations indicate that the hydrodynamic radius is sensitive to changes of the protein net charge and hence it cannot be assumed constant in general. Also, several limitations associated with models for estimating protein net charge and hydrodynamic radius from protein structure, amino acid sequence, and experimental electrophoretic mobility are provided and discussed. These conclusions also show clear requirements for further research.Fil: Piaggio, María Virginia. Universidad Nacional del Litoral; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin
Evaluation of the slip length in the slipping friction between background electrolytes and peptides through the modeling of their capillary zone electrophoretic mobilities
This work analyzes and discusses several physicochemical peptide chain properties that may generate partial or total BGE slip boundary conditions on the surface of peptides migrating as spherical and aspherical particles in CZE. A definition of the BGE slip length is presented which is able to account the effect of particle curvature through the associated metrical coefficients. This definition allows the distinction between partial and total BGE slip lengths. It is also shown that the BGE slip length must be variable on orthotropic aspherical particles surfaces.Fil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Piaggio, María Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); Argentin
Analysis of the interplay among charge, hydration and shape of proteins through the modeling of their CZE mobility data
Electrophorectic mobility data of four proteins are analyzed and interpreted through a physicochemical CZE model, which provides estimates of quantities like equivalent hydrodynamic radius (size), effective charge number, shape orientation factor, hydration, actual pK values of ionizing groups, and pH near molecule, among others. Protein friction coefficients are simulated through the creeping flow theory of prolate spheroidal particles. The modeling of the effective electrophoretic mobility of proteins requires consideration of hydrodynamic size and shape coupled to hydration and effective charge. The model proposed predicts native protein hydrations within the range of values obtained experimentally from other techniques. Therefore, this model provides consistently other physicochemical properties such as average friction and diffusion coefficients and packing fractal dimension. As the pH varies from native conditions to those that are denaturing the protein, hydration and packing fractal dimension change substantially. Needs for further research are also discussed and proposed.Fil: Piaggio, María Virginia. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Peirotti, Marta Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Deiber, Julio Alcides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentin