Browsing by Author "Kler, Pablo A."
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Item Comprehensive model of electromigrative transport in microfluidic paper based analytical devices(2020-01-06) Schaumburg, Federico; Kler, Pablo A.; Berli, Claudio L. A.A complete mathematical model for electromigration in paper-based analytical devices is derived, based on differential equations describing the motion of fluids by pressure sources and EOF, the transport of charged chemical species and the electric potential distribution. The porous medium created by the cellulose fibers is considered like a network of tortuous capillaries and represented by macroscopic parameters following an effective medium approach. The equations are obtained starting from their open-channel counterparts, applying scaling laws and, where necessary, including additional terms. With this approach, effective parameters are derived, describing diffusion, mobility and conductivity for porous media. While the foundations of these phenomena can be found in previous reports, here, all the contributions are analyzed systematically and provided in a comprehensive way. Moreover, a novel electrophoretically driven dispersive transport mechanism in porous materials is proposed. Results of the numerical implementation of the mathematical model are compared with experimental data, showing good agreement and supporting the validity of the proposed model. Finally, the model succeeds in simulating a challenging case of free-flow electrophoresis in paper, involving capillary flow and electrophoretic transport developed in a 2D geometry.Item Corrección de inestabilidades numéricas en simulaciones de fenómenos de transporte reactivos discontinuos(2020) García Aguirre, Octavio; Harispe, David Gabriel; Kler, Pablo A.; Gerlero, Gabriel S.La generación de nuevos materiales funcionales diseñados desde la micro y nano escala es un área de intensa actividad actual. En este marco, son de especial interés los sistemas reactivos que producen precipitaciones complejas con patrones autoorganizados. Si bien se han realizado grandes progresos en los últimos años, la dinámica de dichos procesos no ha sido bien descrita aún. Para ello es necesario comprender cómo los fenómenos de transporte afectan la síntesis en microsistemas. Este conocimiento es crucial para realizar un diseño racional de las estructuras y regular los parámetros de operación durante la síntesis. La simulación computacional, es una herramienta muy útil para acelerar el estudio y la predicción de los sistemas mencionados. Según Pristker, la simulación computacional, se puede definir como el proceso de diseñar un modelo matemático-lógico de un sistema del mundo real y experimentar con el modelo en una computadora. Esto nos permite entender el comportamiento del sistema y/o evaluar estrategias para la operación de éste. Por otro lado, simular sistemas se ha impuesto como una herramienta valiosa particularmente al momento de estudiar procesos que son dependientes de recursos dado que provee una forma rápida y económica para experimentar con diferentes alternativas y enfoques. No obstante, la implementación numérica de modelos que describen estos sistemas reactivos es muy desafiante, dado que en general se trata de sistemas de ecuaciones no-lineales acopladas en dominios multiescala. Dentro de los sistemas reactivos, existen los sistemas reactivos discontinuos como los que dan origen a los denominados patrones de Liesegang. Estos se forman cuando dos compuestos A y B reaccionan, y a partir de determinada concentración crítica, el producto AB precipita en regiones definidas del espacio, formando bandas periódicas. Al presente, existen modelos computacionales 1D que describen este proceso mediante el acople de las ecuaciones de reacción-difusión de cada compuesto, con un término auto catalítico de cristalización y/o precipitación. Sin embargo, actualmente, no se conocen otros modelos numéricos 2D o 3D capaces de simular adecuadamente el fenómeno de generación de patrones de Liesegang.Item Multiphysics approach for fluid and charge transport in paper-based microfluidics(2022-10-08) Franck, Nicolás; Berli, Claudio L. A.; Kler, Pablo A.; Urteaga, Raúl; Franck, N. et al. Multiphysics approach for fluid and charge transport in paper-based microfluidics. Microfluidics and Nanofluidics, Vol. 26: article number 87 (2022).A multiphysic model that simultaneously describe different transport phenomena in porous media is presented. The porous matrix is regarded as a bundle of periodically constricted tubes, whose pore radius distribution is described by a probability density function (PDF). The mathematical basis and the experimental validation of the model are reported. Two different materials frequently used in paper-based microfluidics were used: Whatman #1 and Muntktell 00A filter papers. These substrates were studied by capillary imbibition, hydrostatic pressure-driven flow, and electrical resistance measurements. Different PDFs were evaluated to represent the output of these experiments, and their predictions were quantified by using a Chi-Square test. The model was able to simultaneously describe the three transport phenomena by using the log-normal PDF with two statistical parameters: mean and variance. The formulation avoids including the tortuosity of the flow path, which is commonly employed as an adjusting parameter. The multiphysics model was also successfully used to calculate the parameters of single-physics models, such as Darcy’s permeability and Lucas-Washburn diffusion coefficient. Furthermore, after obtaining a suitable PDF, the proposed model can be applied to different porous materials, as well as to the design of complex paper-based microfluidic devices that combine several types of papers.Item Precise electroosmotic flow measurements on paper substrates(2021-01-12) Franck, Nicolás; Schaumburg, Federico; Urteaga, Raúl; Kler, Pablo A.A novel method for electroosmotic flow (EOF) measurement on paper substrates is presented; it is based on dynamic mass measurements by simply using an analytical balance. This technique provides a more reliable alternative to other EOF measurement methods on porous media. The proposed method is used to increase the amount and quality of the available information about physical parameters that characterize fluid flow on microfluidic paper–based analytical devices (µPADs). Measurements were performed on some of the most frequently used materials for µPADs, i.e. Whatman #1 , S&S and Muntktell 00A filter paper. Obtained experimental results are consistent with the few previously reported data, either experimental or numerical, characterizing EOF in paper substrates. Moreover, a thorough analysis is presented for the quantification of the different effects that affect the measurements such as Joule effect and evaporation. Experimental results enabled, for the first time, to establish well defined electroosmotic characteristics for the three substrates in terms of the magnitude of EOF as funtion of pH, enabling researchers to make a rational choice of the substrate depending on the electrophoretic technique to be implemented. The measurement method can be described as robust, reliable, and affordable enough for being adopted by researchers and companies devoted to electrophoretic µPADs and related technologies.Item Validity of capillary imbibition models in paper-based microfluidic applications(2022-01-04) Gerlero, Gabriel S.; Valdéz, Andrés R.; Urteaga, Raúl; Kler, Pablo A.Paper-based microfluidics has grown continuously over the last few years. One of the most important characteristics of paper-based microfluidic devices is the ability to pump fluids with the single action of capillary forces. However, fluid flow control in paper-based microfluidic devices has been studied primarily through empirical approaches; and as paper-based microfluidic devices have become more complex, more general and precise models of fluid flow are required. Particularly difficult to model are unsaturated flow conditions, which are critical to the overall performance of paper-based analytical devices, which may contain pre-adsorbed reagents such as indicator particles or antibodies. In this work we propose an objective test and a discussion on the suitability of different models (including a novel model derived here from LET-based models) that represent fluid imbibition dynamics in paper substrates. We reproduce experimental fluid fronts with the best parameter fits of the different models to show their actual capabilities to represent the moisture content function and present an analysis of propagation of uncertainties to obtain a final objective quantification of the quality of model fits. This objective analysis will endow the paper-based microfluidics community with objective information about modeling tools to improve the designs and performance of these devices.