Ali Aghvami | Searcharxiv

arXiv2022

Active pulsatile gels: from chemical microreactor to polymeric actuator

We report on a synthesis protocol, experimental characterization and theoretical modeling of active pulsatile Belousov-Zhabotinsky (BZ) hydrogels. Our two-step synthesis technique allows independent optimization of the geometry, the chemical, and the mechanical properties of BZ gels. We identify the role of the surrounding medium chemistry and gel radius for the occurrence of BZ gel oscillations, quantified by the Damkohler number, ratio of chemical reaction to diffusion rates. Tuning the BZ gel size to maximize its chemomechanical oscillation amplitude, we find that its oscillatory strain amplitude is limited by the timescale of gel swelling relative to the chemical oscillation period. Our experimental findings are in good agreement with a Vanag-Epstein model of BZ chemistry and a Tanaka Fillmore theory of gel swelling dynamics.

cond-mat.soft↗

arXiv2021

Effects of confinement on the dynamics and correlation scales in active fluids

We study the influence of solid boundaries on dynamics and structure of active fluids as the height of the container, $z$, changes. Along the varying dimension, the geometry systematically increases, therefore, the confinement ($z$) transits from "strong confinement", to "intermediate confinement" and to "weak confinement" (close to "unconfined"). In horizontal dimensions ($x,y$), the system remains "unconfined". Through tracking the tracers dispersed in the active fluids in three dimensions we observed that activity level, characterized by velocity fluctuations of flow tracers, increases as system size increases. Concomitantly, the velocity-velocity temporal correlation changes from weak correlation to strong positive correlation, indicating "memory" in active flows. We estimate the characteristic size of the flow structure by integrating the velocity-velocity spatial correlation function. The integral increases as confinement becomes weaker and saturates at approximately 400 microns as the system becomes "unconfined". This saturation indicates an intrinsic length scale which, along with the small-scale isotropy, demonstrates the multi-scale nature of this kinesin-driven bundled microtubule system.

cond-mat.soft↗