arXiv subjects

F. J. Galindo-Rosales

Publications and source records attributed to F. J. Galindo-Rosales.

5 recordsLinked to original sources

arXiv2026

Impulsive Hydrodynamic Exfoliation into Monolayer Graphene and Nanofragments by Transonic Flow Focusing

We propose using Transonic Flow Focusing (TFF) to produce 2D and 0D nanomaterials. This technique focuses liquid suspensions into high-speed micrometer-scale jets, combining extremely high shear and elongational stresses in a confined, contact-free zone. For the Graphene Nanoplatelets suspensions and TFF operating conditions investigated here, the process promoted exfoliation without added surfactants or oxidative chemistry. Both graphene monolayer flakes ($\sim 300-400$ nm in lateral size) and monolayer graphene nanofragments with lateral sizes compatible with quantum dots ($\sim 10-15$ nm) were obtained in a single TFF step using isopropanol and pure water. Our theoretical analysis reveals that, during microsecond residence times at the meniscus-jet transition, shear and extensional stresses of the order of $10^6$ s$^{-1}$ act on the suspended particles, yielding viscous power densities of the order of $10^{10}$ $\mathrm{W/m^{3}}$. High-resolution transmission electron microscopy and atomic force microscopy show that the monolayer fraction exceeded 99\% for isopropanol and 92.9\% for water. These results suggest that TFF can combine solvent versatility with a high monolayer fraction in a purely mechanical top-down process.

physics.flu-dyn↗

arXiv2026

Magnetorheological Characterization of Blood Analogues Seeded with Paramagnetic Particles

Magnetic particle under external fields can be useful in various medical applications, gaining access to the whole body if deployed in the bloodstream. Localised drug delivery, haemorrhage control, and cancer treatment are among the applications that have the potential to become revolutionary therapies. Despite this interest, a magnetorheological characterisation of particle-seeded blood has yet to be achieved. In this work, we evaluate the magnetorheological response of blood analogues seeded with paramagnetic particles in different concentrations, under the effects of a uniform, density-varying magnetic field. Through steady shear experiments, we encounter the usual magnetically-induced shear thinning response, and oscillatory shear results point toward significant alterations in the fluids' microstructure. However, experimental limitations make it difficult to accurately evaluate the oscillatory shear response of such rheologically subtle fluids, limiting both the quality and quantity of achievable information. Despite experimental limitations, our results demonstrate that magnetic fields can induce marked and quantifiable rheological changes in seeded blood analogues. The framework established here provides a foundation for future studies on real blood samples and for the design of magnetically responsive biomedical systems.

physics.flu-dyn↗

arXiv2026

Pressure shifts in pulsatile shear: A microfluidic method to probe the normal stress response of complex fluids

A microfluidic approach to probing the first normal stress difference from single-point pressure measurements in transient shear flows is presented. Using an original experimental design, we examine the near-zero-mean pulsatile flow of polymeric solutions in a straight microchannel at low Reynolds and Womersley numbers. An important aspect of this work is that the enhanced fluid elastic stresses can be efficiently determined via the pressure shift measured from pressure-controlled pulsatile shear experiments. We find a scaling law that collapses pressure-shift data from viscoelastic fluids of different molecular weights onto a single master curve that can then be used to predict this phenomenology. Taken together, these results could help shed light on our understanding of the non-linear normal stress responses in time-dependent flows.

physics.flu-dyn↗

arXiv2025

Effects of non-parallelism on standard and magnetorheological measurements

Aiming towards the magnetorheological characterisation of whole human blood, we evaluated the suitability of our experimental setup for steady shear measurements with low-viscosity fluids. Previous measurements with a rotational rheometer equipped with a magnetorheological cell returned low and inconsistent apparent-viscosity values. In this work, a parametric study was conducted, experimentally and numerically, to evaluate the possible error sources and define an experimentally reliable window. Steady shear measurements were carried out with Newtonian fluids using two geometries: parallel-plates at different gap heights, and cone-plate. A clear decrease in measured viscosity with parallel-plate gap reduction was found, along with a slight overestimation of the cone-plate. Numerical results corroborated the experimental observations, pointing towards a small inclination of the bottom plate (between 0.1° and 0.3°). The numerical study has also shown that geometry non-parallelism can lead to significant flow alterations, particularly for cone-plate geometries where contraction/expansion flow can be generated, critically deviating from the canonical Couette flow and provoking non-negligible errors. Additional experimental and numerical work was conducted to evaluate the effects of the non-parallelism on magnetorheological measurements. The geometrical asymmetry results in severe alterations of the microstructural dynamics, possibly leading to an underestimation of the magnetorheological response. This work has shown that geometry non-parallelism can have critical repercussions on simple shear flows, with fundamentally different implications from a general gap-error, and can be identified through comparative measurements with Newtonian fluids in different geometries (parallel-plates and cone-plate)

physics.flu-dyn↗

arXiv2020

A block-coupled Finite Volume methodology for problems of large strain and large displacement

A nonlinear block-coupled Finite Volume methodology is developed for large displacement and large strain regime. The new methodology uses the same normal and tangential face derivative discretisations found in the original fully coupled cell-centred Finite Volume solution methodology for linear elasticity, meaning that existing block-coupled implementations may easily be extended to include finite strains. Details are given of the novel approach, including use of the Newton-Raphson procedure on a residual functional defined using the linear momentum equation. A number of 2-D benchmark cases have shown that, compared with a segregated procedure, the new approach exhibits errors with many orders of magnitude smaller and a much higher convergence rate.

cs.CE↗