Browsing by Author "Urteaga, Raúl"
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Item Determinación del llenado capilar en silicio poroso mediante interferometría de baja coherencia(2017) Sallese, Marcelo; Morel, Eneas Nicolás; Cencha, Luisa; Budini, Nicolás; Urteaga, Raúl; Torga, Jorge RománLa determinación de la dinámica de llenado capilar en estructuras nanoporosas y, en particular, del perfil de la fracción de llenado en el frente de mojado se ha propuesto como un posible método de caracterización de la distribución de poros de la estructura [1]. Así mismo, la dinámica de llenado en estructuras nanoporosas de morfología conocida permite realizar el estudio de propiedades de fluidos en condiciones de gran confinamiento espacial [2]. En este trabajo se propone determinar la dinámica de llenado capilar en estructuras de silicio poroso nanoestructurado mediante la técnica de interferometría de baja coherencia. El ingreso de un líquido dentro de la estructura porosa produce un incremento en el espesor óptico de la capa. La determinación del espesor óptico en función de la posición y del tiempo permite monitorear la dinámica de llenado capilar. El sistema empleado es un interferómetro de una sola rama que utiliza como fuente de luz un láser de gran ancho espectral (~100 nm, centrado en 800 nm), un sistema de fibra óptica y un espectrómetro como sistema de detección. La señal de interferencia se genera por la superposición de las reflexiones en las distintas interfaces de la muestra con una reflexión de referencia (Fig. 1a). A partir del análisis de esta señal es posible medir camino óptico recorrido por el haz al atravesar la muestra. Se determinó el llenado capilar de una muestra de silicio poroso de 30 micrones de espesor y 80% de porosidad utilizando alcohol etílico. La muestra fue sellada en su parte superior con un film de etil-vinil-acetato (EVA) mediante calentamiento controlado del termoplástico (Fig. 1b). Los resultados indican que la dinámica de llenado sigue un comportamiento tipo Washburn (����� ∝ ��������������� ) y se evidencia un ensanchamiento pronunciado del frente de avance (Fig. 1c) que se corresponde con la morfología de la estructura porosa.Item Low-coherence interferometry measurement of filling in porous silicon(2018) Sallese, Marcelo; Torga, Jorge Román; Budini, Nicolás; Urteaga, RaúlThe determination of capillary filling dynamics in nanoporous structures and, in particular, the analysis of the filling fraction profile in the advancing wet front have been proposed as possible methods for characterizing the pore distribution of these structures. Furthermore, the filling dynamics in nanoporous structures of known morphology allows studying fluid properties under conditions of strong spatial confinement. In this work we determine the capillary filling dynamics of porous silicon structures using low-coherence interferometry. When the liquid enters the porous structure there is an increase in the optical thickness of the layer. The determination of optical thickness as a function of position and time allows monitoring capillary filling dynamics. The high spatial resolution of this technique allows to analyze the wet front broadening, which can be used to obtain information about the pore distribution in the sampleItem 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.