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

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

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

On the Viscosity of Concentrated Suspensions of Charged Colloids

This work is concerned with the theoretical estimation of the low-shear viscosity of concentrated suspensions of charged-stabilized latex particles. Calculations are based on the assumption that particles interacting through purely repulsive potentials behave as equivalent hard-spheres (HS), and suspension viscosity may be analyzed in the framework of HS systems. In order to predict numerically the HS radius, the pair potential due to double-layer interaction, as a function of particle concentration, was investigated by using Poisson-Boltzmann theory and the cell model. Calculations explain appropriately experimental data for a wide range of particle sizes, volume fractions and salt concentrations. The problem concerning the effective surface charge of latex particles is also discussed.Fil: Berli, Claudio Luis Alberto. 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; ArgentinaFil: Quemada, Daniel. Universite Paris VII; Franci

Procedure to Evaluate the Shear Rate Profile and the Apparent Viscosity of Non-Newtonian Fluids in the Falling Cylinder Viscometer

The falling cylinder viscometer (FCV) is a reliable instrument to quantify the viscosity of Newtonian fluids. Nevertheless, when non-Newtonian fluids are tested in this device, difficulties appear to determine the apparent viscosity. Thus, conventional rheometric calculations cannot be ap-plied directly to experimental data provided by the FCV in order to obtain the apparent viscosity func-tion, because the knowledge of a rather complex shear rate profile in the annular flow, between the falling cylinder and the container, is required. Con-sequently, experimental data of the FCV must be processed numerically by including inevitably an appropriate model of the apparent viscosity for the fluid under study. Previous works used the Power Law model, within several small sub-regions of shear rates, selected heuristically, as a reasonable ap-proximation. The present work proposes an algo-rithm to process the experimental data provided by the FCV for different non-Newtonian fluids. Thus, this generic procedure allows one to perform calcu-lations for any model of the apparent viscosity that includes a set of parameters to be appropriately identified.Fil: Berli, Claudio Luis Alberto. 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

Theoretical Analysis of the Gravity Driven Capillary Viscometers

Gravity-driven capillary viscometers (GDCVs) are used to obtain the viscosity function of non-Newtonian fluids from measurements of the instantaneous fluid height in the overhead reservoir. The reliability of this viscometry depends on two main aspects: the accomplishment of the required flow condition in the apparatus and the appropriate conversion of raw data into rheometric functions. This work presents a rigorous theoretical analysis of the GDCV, thus providing criteria to achieve accurate measurements. The equations describing the rheometric flow in a GDCV are deduced from the basic laws of momentum and mass conservation. From these equations, the flow dynamics of the apparatus is studied and the constraints required to attain a quasi-steady-state flow are established. Under these conditions, the rheometric functions are written in terms of the instantaneous fluid height. In addition, a method to process experimental data of non-Newtonian fluids is proposed, which can handle the ill-posed problem associated with the determination of the viscosity function in this viscometry.Fil: Berli, Claudio Luis Alberto. 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

Caracterización Reocinética de Soluciones Precursoras de Gelatina y Glutaraldehído para la Formación de Hidrogeles

Las cadenas polianfolíticas de gelatina en solución sepueden unir covalentemente con glutaraldehído (GTA) para formar matrices deuniones covalentes capaces de hidratarse en presencia de soluciones acuosas,formando lo que usualmente se denominan hidrogeles de gelatina. La uniónquímica entre cadenas se basa en la reacción de GTA con grupos aminos libres delos aminoácidos lisina o hidroxilisina presentes en las cadenas polipeptídicas.Para obtener estos hidrogeles adecuadamente formulados, en relación a laspropiedades mecánicas finales, se requiere primero la caracterizaciónreométrica-reológica de la solución precursora de GTA y gelatina a través de lafunción reométrica denominada viscosidad de corte mediante diferentes historiasmecánicas. La transición sol-gel en condiciones de reposo se puede describir através de un parámetro estructural básico que evoluciona al valor depercolación. En este contexto, dos respuestas asintóticas están bienidentificadas para el proceso de gelificación de soluciones macromoleculares (Ottoneet al., 2009). Una es la viscosidad inicial de la solución asociada a unparámetro estructural nulo (no está formada la miscroestructura). La otra es laviscosidad de percolación a velocidad de corte cero (suponiendo un valorinfinito cuando alcanza el punto de gelificación) y corresponde al valor máximodel parámetro estructural. En condiciones de flujo, es posible convertirdirectamente los datos experimentales de viscosidad de corte en función deltiempo para una velocidad de corte prefijada, en la evolución del parámetroestructural. En este trabajo se realizan ensayos reométricos a velocidades decorte constantes en una celda cono-plato y se evalúa la viscosidad de corte enfunción del tiempo de maduración de la solución precursora. Luego se aplica unmodelo reocinético que involucra el parámetro estructural formulado en laliteratura para soluciones concentradas de gelatina y suspensiones departículas colagénicas (Ottone et al., 2009, Deiber et al., 2011). Este modelocontempla la formación de microestructuras por enlaces químicos e interaccionesfísicas, y la destrucción mecánica de la misma.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: 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

A Numerical method for the Viscoelastic Melt Spinning Model with Radial resolutions of Temperature and Stress Fields

A numerical method to compute the viscoelastic melt-spinning model with radial resolutions of temperature and stress fields is formulated and applied to the low speed range. The starting framework is the reduction of the complete continuous model into both the perturbed two-dimensional model and the perturbed average model obtained from a first-order regular perturbation analysis available in the literature. The polymer rheology is described with the nonisothermal Phan-Thien and Tanner and Giesekus constitutive equations. By using the implicit tridiagonal scheme of finite differences coupled to the fourth-order Runge−Kutta method, an iterative numerical algorithm is proposed for the computation of the coupled balance equations. The temperature and stress fields in the filament as functions of axial and radial positions are obtained for a well-refined mesh and with high numerical precision. The numerical algorithm considers the appropriate interplay between axial and radial varying temperature and stress fields and the rigorous averaged balances of momentum and energy and averaged constitutive equation. The development of a skin-core structure is predicted with the two rheological models.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: 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