arXiv subjects

Ryker Fish

Publications and source records attributed to Ryker Fish.

3 recordsLinked to original sources

arXiv2025

Emergent clusters in strongly confined systems

Driven suspensions, where energy is input at a particle scale, are a framework for understanding general principles of out-of-equilibrium organization. A large number of simple interacting units can give rise to non-trivial structure and hierarchy. Rotationally driven colloidal particles are a particularly nice model system for exploring this pattern formation, as the dominant interaction between the particles is hydrodynamic. Here, we use experiments and large-scale simulations to explore how strong confinement alters dynamics and emergent structure at the particle scale in these driven suspensions. Surprisingly, we find that large-scale (many times the particle size) density fluctuations emerge as a result of confinement, and that these density fluctuations sensitively depend on the degree of confinement. We extract a characteristic length scale for these fluctuations, demonstrating that the simulations quantitatively reproduce the experimental pattern. Moreover, we show that these density fluctuations are a result of the large-scale recirculating flow generated by the rotating particles inside a sealed chamber. This surprising result shows that even when system boundaries are far away, they can cause qualitative changes to mesoscale structure and ordering.

cond-mat.soft↗

arXiv2025

libMobility: A Python library for hydrodynamics at the Smoluchowski level

Effective hydrodynamic modeling is crucial for accurately predicting fluid-particle interactions in diverse fields such as biophysics and materials science. Developing and implementing hydrodynamic algorithms is challenging due to the complexity of fluid dynamics, necessitating efficient management of large-scale computations and sophisticated boundary conditions. Furthermore, adapting these algorithms for use on massively parallel architectures like GPUs adds an additional layer of complexity. This paper presents the libMobility software library, which offers a suite of CUDA-enabled solvers for simulating hydrodynamic interactions in particulate systems at the Rotne-Prager-Yamakawa (RPY) level. The library facilitates precise simulations of particle displacements influenced by external forces and torques, including both the deterministic and stochastic components. Notable features of libMobility include its ability to handle linear and angular displacements, thermal fluctuations, and various domain geometries effectively. With an interface in Python, libMobility provides comprehensive tools for researchers in computational fluid dynamics and related fields to simulate particle mobility efficiently. This article details the technical architecture, functionality, and wide-ranging applications of libMobility. libMobility is available at https://github.com/stochasticHydroTools/libMobility.

cond-mat.soft↗

arXiv2025

Persistence of Coffee-Ring Deposits in Concentrated Suspensions of Anisotropic Colloids

Evaporating a droplet containing dispersed colloids leaves behind a dried deposit whose shape is determined by capillary flows and the resulting particle transport. The classical coffee-ring effect occurs when an outward radial flow drives particles toward the droplet's contact line as the droplet evaporates, resulting in uneven deposition. This deposition is often studied in dilute concentration regimes where, hydrodynamically, the effects of particle shape are unimportant. As particle concentration increases, it is expected that particle anisotropy should play a larger role in modifying transport and potentially suppressing coffee-ring formation. We present experiments isolating the effects of particle shape, concentration, and density, as well as solvent temperature, on the geometry of the ring deposit. By analyzing the deposits using surface profilometry to more accurately characterize ring widths, these experiments show that coffee-ring formation is independent of particle anisotropy and is instead controlled by the ratio of the particle sedimentation velocity to the velocity of the droplet's evaporating air-water interface. Hydrodynamic simulations support this finding by providing quantitative estimates for bulk sedimentation velocity. Together, these results offer a unified picture of how multiple physical parameters determine coffee-ring geometry with direct implications for suppressing uneven deposition in practical applications.

cond-mat.soft↗