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

Aging, rejuvenation and thixotropy in yielding magnetorheological fluids

The yielding behavior of dilute magnetorheological (MR) fluids has been investigated using creep–recovery tests. At very low stress levels, MR fluids behave in the linear viscoelastic regime as demonstrated by the fact that the instantaneous strain equals the instantaneous (elastic) recovery. In this region, gap-spanning field-induced structures support the stress levels applied. Upon increasing the stress value, the MR fluid evolves towards a nonlinear viscoelastic response. Here, the retarded elastic and viscous strain decrease, and the plastic contribution to the instantaneous strain grows probably due to the appearance of unattached field-induced structures. A larger stress value results in a viscoplastic solid behavior with negligible retarded and viscous strain and a fully plastic instantaneous strain. Finally, a plastic fluid behavior is found when the stress value is larger than the so-called yield stress. MR fluids exhibit an intermediate behavior between non-thixotropic (simple) and highly thixotropic model yield stress fluids.Fil: de Vicente, Juan. Universidad de Granada; España;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 (i); Argentina

Numerical simulation of electrokinetic flow in microfluidic chips

Microfluidic chips are miniaturized analytical devices used in chemical, biological and medical applications. In most cases, fluids are conducted through microchannels by applying electric potentials and/or pressure gradients. This growing lab-on-a-chip technology requires numerical simulations to assist the design, control and optimization of analytical manipulations. The present work deals with FEM-based calculations of the dynamics of electrolyte solutions in cross-shaped microchannels, where the flow is driven by the action of external electric fields. A theoretical modeling of electrokinetic and transport phenomena in the system is carried out in the framework of continuum fluid mechanics. Calculations ground on conservation equations of mass, momentum and electrical charge, considering effects in three dimensions. Operations normally performed in analytical systems are discussed, such as loading, focusing, and injection of samples. Numerical simulations carried out in this work can be a valuable tool to control and optimize practical manipulations in microfluidic chips.Fil: Guarnieri, Fabio Ariel. 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: Kler, Pablo Alejandro. 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: 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; Argentin

Simulation of 1d and 2d electrophoretic separations in microfluidics chips

Electrophoretic separations comprise a group of analytical techniques such as capillary zone electrophoresis (CZE), isoelectric focusing (IEF), isotachophoresis (ITP) and free flow electrophoresis (FFE). In all cases, separation is based on the dissimilar mobility of ionic species under the action of an external electric field. These techniques, which are widely used in chemical and biochemical analysis, have been miniaturized in the last years and now represent one of the most important applications of the lab-on-a-chip technology. In a previous work, a generalized numerical model of electrophoresis on microfluidic devices was presented. The model is based on the set of equations that governs electrical phenomena (Poisson equation), fluid dynamics (Navier-Stokes equations), mass transport (Nerst-Planck equation) and chemical reactions. Also the relationship between the buffer characteristics (ionic strength, pH) and surface potential of channel walls is taken into consideration. In this work, three application examples are presented: (a) an IEF assay with immobilized pH gradient (IPG) including the influence of electro-osmotic flow on its performance, (b) an IEF assay involving ampholyte-based pH gradient, and (c) a 2D electrophoresis, involving FFIEF plus CZE. The numerical simulation is carried out by using PETSc-FEM (Portable Extensible Toolkit for Scientific Computation - Finite Elements Method), in a Python environment developed at CIMEC using high performance parallel computing and solving techniques based on domain decomposition methods.Fil: Kler, Pablo Alejandro. 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: Guarnieri, Fabio Ariel. 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; Argentina. Universidad Nacional de Entre Rios; ArgentinaFil: 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; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentin

Generalized numerical model for the simulation of electrophoretic methods in microfluidic chips

Electrophoretic methods are separation techniques based on the mobility of ions under the action of an external electric field. These techniques, which are widely used in chemical and biochemical analysis, have been miniaturized in the last years and now represent one of the most important applications of the lab-on-a-chip technology. In this work, a generalized numerical model of electrophoresis on microfluidic devices is presented. The model is based on the set of equations that governs electrical phenomena (Poisson equation), fluid dynamics (Navier-Stokes equations), mass transport (Nerst-Planck equation) and chemical reactions. The model is said to be generalized because it covers different techniques such as capillary eletrophoresis and isoelectric focusing, and allows to simulate processes involving multiple analytes and complex electrolytes buffers. Moreover, the relationship between the buffer characteristics (ionic strength, pH) and physicochemical properties of channel walls is taken into consideration. The numerical simulation is carried out by using PETSC-FEM (Portable, Extensible Toolkit for Scientific Computation - Finite Elements Method), in a Python environment developed at CIMEC using high performance parallel computing and solving techniques based on domain decomposition methods. Finally, examples of interest involving electrophoresis on chips are considered as study cases.Fil: Kler, Pablo Alejandro. 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: Guarnieri, Fabio Ariel. 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: 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; Argentin

Optofluidic study of the pore widening in nanoporous alumina membranes

En este trabajo se utiliza una técnica optofluídica para estudiar el ensanchamiento químico de los poros de membranas de alúmina nanoporosa. La técnica optofluídica consiste en medir la evolución de la reflectancia de luz láser producida por la membrana durante la imbibición capilar de la misma con un líquido de propiedades conocidas. El cambio en la proporción aire-líquido a medida que la membrana se llena modifica el índice de refracción efectivo de la membrana produciendo sucesivamente interferencias constructivas y destructivas. La señal obtenida puede relacionarse con el volumen de líquido que penetró en la membrana utilizando una teoría de medio efectivo. Realizando las medidas de llenado capilar en ambas direcciones de la membrana es posible caracterizar la morfología del poro. Los resultados obtenidos indican que los poros de las membranas utilizadas son inicialmente cónicos y que el ensanchamiento por ataque químico con soluciones diluidas de H3PO4 es uniforme a lo largo de los mismos y proporcional al tiempo de ataque. Los resultados obtenidos son consistentes con los que produce la caracterización de las membranas por técnicas estándar de elipsometría y demuestran que esta nueva técnica optofluídica constituye una forma simple y rápida de caracterizar membranas nanoporosas. La porosidad de las membranas obtenida con esta técnica difiere de la encontrada a partir del análisis de imágenes de las muestras. Se sugiere que parte del líquido que ingresa en la membrana ocupa una sub-porosidad formada por defectos en la matriz de alúmina.In this paper we use an optofluidic technic for study the chemical pore widening process of nanoporous alumina membranes. This technic consists in measure the time evolution of the membrane reflectance during capillary imbibition of a liquid with known properties. The change in the proportion air-liquid inside the membrane, modify the effective refractive index producing successively constructive and destructive interferences. Using an effective medium theory, the obtained signal can be related with the liquid volume inside the membrane. Additionally, this information can be processed to characterize the morphology of the pores. The obtained results indicate that, initially, the pores are conical and the chemical etching with diluted H3PO4 solutions is produced in an axially uniform way at constant rate. These results are consistent with those obtained with standard ellipsometry technics and show that this novel optofluidic technic is simple, fast and suitable for characterization of nanoporous membranes. However, the porosity value obtained differs with those obtained from SEM images analysis. This result suggests that a portion of the liquid used enters to a sub-nano porosity formed by defects in the alumina matrix.Fil: Elizalde, Emanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Rahman, M.M.. Universitat Rovira I Virgili; EspañaFil: Urteaga, Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: 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: Koropecki, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin

Microfluidics-based encapsulation of isoniazid in egg white/carrageenan microparticles for sustained release

The prevalence of tuberculosis continuously grows and there is an imperious need to improve the therapeutic efficacy of approved drugs for clinical use. Here we report the encapsulation of isoniazid (INH) in egg white/ - carrageenan microparticles, which are intended for drug vehiculation through the gastrointestinal tract and con- trolled release in the ileum. Spherical and highly monodisperse microparticles (255 mm average diameter) were obtained by droplet-based microfluidics and subsequent microwave irradiation. The entire amount of INH added to the particles was encapsulated. Infrared spectra revealed the formation of esters, hydrogen bonding, and Mail- lard reaction in the biopolymer matrix. In vitro release experiments were carried out in media that systematically emulate the stomach and intestinal tract conditions: 37 °C, NaCl 0.05 mol/L, pH 1.6, for the first 2 h, and Tris?HCl 0.1 mol/L, pH 7, for the next 24 h. A small fraction of the loaded INH was released in the first medium and most of the drug was progressively delivered in the second medium. The release profiles of microparticles were analyzed by using classical kinetic models, which enabled to hypothesize the release mechanism of INH from the biopolymer matrix. This knowledge, together with the ability to control the governing parameters of microfluidic elaboration, opens further possibilities for designing optimal prototypes for sustained release.Fil: Marengo, Robinson Cristian. Universidad Nacional del Litoral; ArgentinaFil: Mengatto, Luciano Nicolas. 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: Olivares, María Laura. 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: 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; Argentin

Precursor Film Spreading during Liquid Imbibition in Nanoporous Photonic Crystals

When a macroscopic droplet spreads, a thin precursor film of liquid moves ahead of the advancing liquid-solid-vapor contact line. Whereas this phenomenon has been explored extensively for planar solid substrates, its presence in nanostructured geometries has barely been studied so far, despite its importance for many natural and technological fluid transport processes. Here we use porous photonic crystals in silicon to resolve by light interferometry capillarity-driven spreading of liquid fronts in pores of few nanometers in radius. Upon spatiotemporal rescaling the fluid profiles collapse on master curves indicating that all imbibition fronts follow a square-root-of-time broadening dynamics. For the simple liquid (glycerol) a sharp front with a widening typical of Lucas-Washburn capillary-rise dynamics in a medium with pore-size distribution occurs. By contrast, for a polymer (PDMS) a precursor film moving ahead of the main menisci entirely alters the nature of the nanoscale transport, in agreement with predictions of computer simulations.Fil: Cencha, Luisa Guadalupe. 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: Dittrich, Guido. Hamburg University Of Technology; AlemaniaFil: Huber, Patrick. Universitat Hamburg; AlemaniaFil: 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: Urteaga, Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin