Person: Martín Roca, José
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First Name
José
Last Name
Martín Roca
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Estructura de la Materia, Física Térmica y Electrónica
Area
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7 results
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Now showing 1 - 7 of 7
Item Simulating Microswimmers Under Confinement With Dissipative Particle (Hydro) Dynamics(Frontiers in physics, 2022) Barriuso Gutiérrez, Carlos Miguel; Martín Roca, José; Bianco, Valentino; Pagonabarraga, Ignacio; Valeriani, ChantalIn this work we study microwimmers, whether colloids or polymers, embedded in bulk or in confinement. We explicitly consider hydrodynamic interactions and simulate the swimmers via an implementation inspired by the squirmer model. Concerning the surrounding fluid, we employ a Dissipative Particle Dynamics scheme. Differently from the Lattice-Boltzmann technique, on the one side this approach allows us to properly deal not only with hydrodynamics but also with thermal fluctuations. On the other side, this approach enables us to study microwimmers with complex shapes, ranging from spherical colloids to polymers. To start with, we study a simple spherical colloid. We analyze the features of the velocity fields of the surrounding solvent, when the colloid is a pusher, a puller or a neutral swimmer either in bulk or confined in a cylindrical channel. Next, we characterise its dynamical behaviour by computing the mean square displacement and the long time diffusion when the active colloid is in bulk or in a channel (varying its radius) and analyze the orientation autocorrelation function in the latter case. While the three studied squirmer types are characterised by the same bulk diffusion, the cylindrical confinement considerably modulates the diffusion and the orientation autocorrelation function. Finally, we focus our attention on a more complex shape: an active polymer. We first characterise the structural features computing its radius of gyration when in bulk or in cylindrical confinement, and compare to known results obtained without hydrodynamics. Next, we characterise the dynamical behaviour of the active polymer by computing its mean square displacement and the long time diffusion. On the one hand, both diffusion and radius of gyration decrease due to the hydrodynamic interaction when the system is in bulk. On the other hand, the effect of confinement is to decrease the radius of gyration, disturbing the motion of the polymer and thus reducing its diffusion.Item Rheology of Pseudomonas fluorescens biofilms: From experiments to predictive DPD mesoscopic modeling(Journal of chemical physics, 2023) Martín Roca, José; Bianco, Valentino; Alarcón, Francisco; Monnappa, Ajay K.; Natale, Paolo; Monroy, Francisco; Orgaz Martín, Belén; López Montero, Iván; Valeriani, ChantalBacterial biofilms mechanically behave as viscoelastic media consisting of micron-sized bacteria cross-linked to a self-produced network of extracellular polymeric substances (EPSs) embedded in water. Structural principles for numerical modeling aim at describing mesoscopic viscoelasticity without losing details on the underlying interactions existing in wide regimes of deformation under hydrodynamic stress. Here, we approach the computational challenge to model bacterial biofilms for predictive mechanics in silico under variable stress conditions. Up-to-date models are not entirely satisfactory due to the plethora of parameters required to make them functioning under the effects of stress. As guided by the structural depiction gained in a previous work with Pseudomonas fluorescens [Jara et al., Front. Microbiol. 11, 588884 (2021)], we propose a mechanical modeling by means of Dissipative Particle Dynamics (DPD), which captures the essentials of topological and compositional interactions between bacterial particles and cross-linked EPS-embedding under imposed shear. The P. fluorescens biofilms have been modeled under mechanical stress mimicking shear stresses as undergone in vitro. The predictive capacity for mechanical features in DPD-simulated biofilms has been investigated by varying the externally imposed field of shear strain at variable amplitude and frequency. The parametric map of essential biofilm ingredients has been explored by making the rheological responses to emerge among conservative mesoscopic interactions and frictional dissipation in the underlying microscale. The proposed coarse grained DPD simulation qualitatively catches the rheology of the P. fluorescens biofilm over several decades of dynamic scaling. Published under an exclusive license by AIP Publishing.Item Field-Pulse-Induced Annealing of 2D Colloidal Polycrystals(Nanomaterials, 2023) Martín Roca, José; Horcajo Fernández, Manuel; Valeriani, Chantal; Gámez, Francisco; Martinez Pedrero, FernandoTwo-dimensional colloidal crystals are of considerable fundamental and practical importance. However, their quality is often low due to the widespread presence of domain walls and defects. In this work, we explored the annealing process undergone by monolayers of superparamagnetic colloids adsorbed onto fluid interfaces in the presence of magnetic field pulses. These systems present the extraordinary peculiarity that both the extent and the character of interparticle interactions can be adjusted at will by simply varying the strength and orientation of the applied field so that the application of field pulses results in a sudden input of energy. Specifically, we have studied the effect of polycrystal size, pulse duration, slope and frequency on the efficiency of the annealing process and found that (i) this strategy is only effective when the polycrystal consists of less than approximately 10 domains; (ii) that the pulse duration should be of the order of magnitude of the time required for the outer particles to travel one diameter during the heating step; (iii) that the quality of larger polycrystals can be slightly improved by applying tilted pulses. The experimental results were corroborated by Brownian dynamics simulations.Item Characterization of MIPS in a suspension of repulsive active Brownian particles through dynamical features(Journal of chemical physics, 2021) Martín Roca, José; Martínez, Raúl; Alexander, Lachlan C.; Díez, Ángel Luis; Aarts, Dirk G. A. L.; Alarcón, Francisco; Ramírez, Jorge; Valeriani, ChantalWe study a two-dimensional system composed by Active Brownian Particles (ABPs), focusing on the onset of Motility Induced Phase Separation (MIPS), by means of molecular dynamics simulations. For a pure hard-disk system with no translational diffusion, the phase diagram would be completely determined by their density and Peclet number. In our model, two additional effects are present: translational noise and the overlap of particles; we study the effects of both in the phase space. As we show, the second effect can be mitigated if we use, instead of the standard Weeks-Chandler-Andersen potential, a stiffer potential: the pseudo-hard sphere potential. Moreover, in determining the boundary of our phase space, we explore different approaches to detect MIPS and conclude that observing dynamical features, via the non-Gaussian parameter, is more efficient than observing structural ones, such as through the local density distribution function. We also demonstrate that the Vogel-Fulcher equation successfully reproduces the decay of the diffusion as a function of density, with the exception of very high densities. Thus, in this regard, the ABP system behaves similar to a fragile glass.Item Dynamical anomalies and structural features of active Brownian particles characterized by two repulsive length scales(Journal of chemical physics, 2022) Martín Roca, José; Martínez, Raúl; Martínez Pedrero, Fernando; Ramírez, Jorge; Valeriani, ChantalIn this work, we study a two-dimensional system composed by Active Brownian Particles (ABPs) interacting via a repulsive potential with two length scales-a soft shell and a hard core. Depending on the ratio between the strength of the soft shell barrier and the activity, we find two regimes: If this ratio is much larger or smaller than 1, the observed behavior is comparable with ABPs interacting via a single length scale potential. If this ratio is similar to 1, the two length scales are relevant for both structure and dynamical properties. On the structural side, when the system exhibits a motility induced phase separation, the dense phase is characterized by new and more complex structures compared with the hexatic phase observed in single length scale systems. From the dynamic analysis, we find, to our knowledge, the first manifestation of a dynamic heterogeneity in active particles, reminiscent of the glassy dynamics widely studied in passive colloids.Item Magnetic colloidal currents guided on self‐assembled colloidal tracks(Advanced Functional Materials, 2023) Martín Roca, José; Ortega Gómez, Francisco; Valeriani, Chantal; González Rubio, Ramón; Martínez Pedrero, FernandoThe nondiffusive directional transport of micro-cargos, such as colloids, cells, or liposomes, is vital for living organisms, for example in the intracellular transport of cytoplasmic organelles along actin filaments or microtubules, and also in numerous applications in biomedicine and nanotechnology. Mimicking natural designs, the self-assembly capacity of magnetic colloids is studied and exploited to construct different paths along which swarms of magnetic micro/nanoparticles can be guided. Driven transport is possible thanks to the combined effect of the magnetic microstructure of the self-assembled tracks, adsorbed on a solid interface, and the application of a time-dependent magnetic field. Nonadsorbed magnetic particles propel along the pre-formed structures under the action of an externally controllable traveling potential ratchet, like molecular walkers. The transport mechanisms are determined by both the properties of the particles and the configuration of the applied field. Finally, it is shown how the proposed combination of self-assembly and guided transport paves the way to the development of a new class of techniques, able to adapt ad hoc to the environment, and transport of microparticles along irregular profiles and/or crowded conditions. The technological interest is immediate, including drug delivery and controlled guidance of microcargos, in biological environments and microfluidic platforms.Item Rotating Micro-Spheres for adsorption monitoring at a fluid interface(Journal of Colloid and Interface Science, 2022) Martín Roca, José; Jiménez, M.; Ortega, F.; Calero, C.; Valeriani, Chantal; Rubio, R. G.; Martínez Pedrero, F.Hypothesis: A broad range of phenomena, such as emulsification and emulsion stability, foam formation or liquid evaporation, are closely related to the dynamics of adsorbing colloidal particles. Elucidation of the mechanisms implied is key to a correct design of many different types of materials. Experiments: Microspheres forced to rotate near a fluid interface exhibit a roto-translational hydrodynamic mechanism that is hindered by capillary torques as soon as the particles protrude the interface. Under these conditions, the time evolution in the ratio of moving spheres provides a direct description of the adsorption kinetics, while microscopy monitoring of particle acceleration\deceleration informs about the adsorption\desorption dynamics. In this work, the proposed strategy is applied at an air/water interface loaded with spherical magnetic particles negatively charged, forced to rotate by the action of a rotating magnetic field. Findings: The proposed method enables the adsorption/desorption dynamics to be followed during the earliest phase of the process, when desorption of a small fraction of particles is detected, as well as to estimate approximated values of the adsorption/desorption constants. The results obtained show that the addition of a monovalent salt or a cationic (anionic) surfactant promotes (inhibits) both adsorption and formation of permanent bonds between particles. (c) 2022 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).