arXiv subjects

Aurora Hernandez-Machado

Publications and source records attributed to Aurora Hernandez-Machado.

7 recordsLinked to original sources

arXiv2025

Mathematical model of fluid front dynamics driven by porous media pumps

Air-permeable porous media hosts air within their pores. Upon removal from the interior of the material, these porous media have the tendency to reabsorb air from the surrounding, acting as a suction pump. Therefore, the technique used to convert porous media into a pump, consists of degassing the material to remove their air inside. The suction property when recovering the air, can be used to move a liquid through a microfluidic channel. Porous media pumps are very accurate devices to move liquids in a completely controlled way. {By studying the dynamics of the liquid front moved by these pumps, it is possible to extract characteristic properties of both the fluid and the porous material.} In this article, we have developed a theoretical mathematical model that precisely characterizes the dynamics of a liquid moved by a degassed porous media pump through a microchannel by comparing it with experimental data. {We have seen the differences between sealing the external surface of the pump so that it cannot absorb air from the outside, both mathematically and experimentally.} We have observed that, in all cases, the theory fits satisfactorily with the experiments, corroborating the validity of the model. The creation of microfluidic pumps using porous media can be a very useful tool in various fields due to its long operating time, small size and the fact that it operates without any external power source.

physics.flu-dyn↗

arXiv2024

Microfluidic front dynamic for the characterization of pumps for long-term autonomous microsystems

To facilitate the use and portability of Lab on a chip technology, it is desirable to avoid the use of bulky electronic systems for flow control. Developed self-powered microsystems typically move only small volumes of fluid performing up to one or two hours. We have previously shown that polymeric micropumps combined with plastic microfluidic cartridges constitute a universal self-powered modular microfluidic architecture suitable for moving large volumes of fluids in short times. Herein, we show that polymeric micropumps can provide self-powered flow control for long periods of time in the range of hours and days. The calibration curves of various types of micropumps were obtained including one that maintained the movement of the fluid for 23 hours, advancing the fluid front up to 1.8 meters through a channel with a section of 0.127 mm2. We found that the actuation time of the pump was related to degassing time, the effective surface area and the air recovery rate of the pump. This is the first example of a long operating self-powered microsystem, which may have a great impact in those cases where controlled flow is needed for a long period of time and the use of electronic equipment is not desirable.

physics.flu-dyn↗

arXiv2023

Vesicle formation induced by thermal fluctuations

The process of fission and vesicle formation depends on the geometry of the membrane that will split. For instance, a flat surface finds it difficult to form vesicles because of the lack of curved regions where to start the process. Here we show that vesicle formation can be promoted by temperature, by using a membrane phase field model with Gaussian curvature. We find a phase transition between fluctuating and vesiculation phases that depends on temperature, spontaneous curvature, and the ratio between bending and Gaussian moduli. We analysed the energy dynamical behaviour of these processes and found that the main driving ingredient is the Gaussian energy term, although the curvature energy term usually helps with the process as well. We also found that the chemical potential can be used to investigate the temperature of the system. Finally we address how temperature changes the condition for spontaneous vesiculation for all geometries, making it happen in a wider range of values of the Gaussian modulus.

cond-mat.soft↗

arXiv2011

Growth saturation of unstable thin films on transverse-striped hydrophilic-hydrophobic micropatterns

Using three-dimensional numerical simulations, we demonstrate the growth saturation of an unstable thin liquid film on micropatterned hydrophilic-hydrophobic substrates. We consider different transverse-striped micropatterns, characterized by the total fraction of hydrophilic coverage and the width of the hydrophilic stripes. We compare the growth of the film on the micropatterns to the steady states observed on homogeneous substrates, which correspond to a saturated sawtooth and growing finger configurations for hydrophilic and hydrophobic substrates, respectively. The proposed micropatterns trigger an alternating fingering-spreading dynamics of the film, which leads to a complete suppression of the contact line growth above a critical fraction of hydrophilic stripes. Furthermore, we find that increasing the width of the hydrophilic stripes slows down the advancing front, giving smaller critical fractions the wider the hydrophilic stripes are. Using analytical approximations, we quantitatively predict the growth rate of the contact line as a function of the covering fraction, and predict the threshold fraction for saturation as a function of the stripe width.

cond-mat.soft↗

arXiv2010

Activity statistics, avalanche kinetics, and velocity correlations in surface growth

We investigate the complex spatio-temporal dynamics in avalanche driven surface growth by means of scaling theory. We study local activity statistics, avalanche kinetics, and temporal correlations in the global interface velocity, obtaining different scaling relationships among the involved critical exponents depending on how far from or close to a critical point the system is. Our scaling arguments are very general and connect local and global magnitudes through several scaling relationships. We expect our results to be applicable in a wide range of systems exhibiting interface kinetic roughening driven by avalanches of local activity, either critical or not. As an example we apply the scaling theory to analyze avalanches and roughening of forced-flow imbibition fronts in excellent agreement with phase-field numerical simulations.

cond-mat.stat-mech↗

arXiv2010

Dynamics of gravity driven three-dimensional thin films on hydrophilic-hydrophobic patterned substrates

We investigate numerically the dynamics of unstable gravity driven three-dimensional thin liquid films on hydrophilic-hydrophobic patterned substrates of longitudinal stripes and checkerboard arrangements. The thin film can be guided preferentially on hydrophilic longitudinal stripes, while fingers develop on adjacent hydrophobic stripes if their width is large enough. On checkerboard patterns, the film fingering occurs on hydrophobic domains, while lateral spreading is favoured on hydrophilic domains, providing a mechanism to tune the growth rate of the film. By means of kinematical arguments, we quantitatively predict the growth rate of the contact line on checkerboard arrangements, providing a first step towards potential techniques that control thin film growth in experimental setups.

cond-mat.soft↗

arXiv2002

Experiments of Interfacial Roughening in Hele-Shaw Flows with Weak Quenched Disorder

We have studied the kinetic roughening of an oil--air interface in a forced imbibition experiment in a horizontal Hele--Shaw cell with quenched disorder. Different disorder configurations, characterized by their persistence length in the direction of growth, have been explored by varying the average interface velocity v and the gap spacing b. Through the analysis of the rms width as a function of time, we have measured a growth exponent beta ~= 0.5 that is almost independent of the experimental parameters. The analysis of the roughness exponent alpha through the power spectrum have shown different behaviors at short (alpha_1) and long (alpha_2) length scales, separated by a crossover wavenumber q_c. The values of the measured roughness exponents depend on experimental parameters, but at large velocities we obtain alpha_1 ~= 1.3 independently of the disorder configuration. The dependence of the crossover wavenumber with the experimental parameters has also been investigated, measuring q_c ~ v^{0.47} for the shortest persistence length, in agreement with theoretical predictions.

cond-mat.dis-nn↗