Understanding the motion of artificial active swimmers in complex surroundings, such as a dense bath of passive particulate matter, is essential for their successful utilization as cargo (drug) carriers and sensors or for medical imaging, under microscopic domains. In this study, we experimentally investigated the motion of active SiO2–Pt Janus particles (JPs) in a two-dimensional bath of smaller silica tracers dispersed with varying areal densities. Our observations indicate that when an active JP undergoes a collision with an isolated tracer, their interaction can have a significant impact on the swimmer’s motion. However, the overall impact of tracers on the active JPs’ motion (translation and rotation) depends on the frequency of collisions and also on the nature of the collision, which is marked by the time-duration for which the particles maintain contact during the collisions. Further, in the high-density tracer bath, our experiments reveal that the motion of the active JP results in a novel organizational behavior of the tracers on the trailing Pt (depletion of tracers) and the leading SiO2 (accumulation of tracers) side. In laboratory frame the emergence and the subsequent vanishing of the depletion zone are discussed in detail.
Nature is filled with various living organisms, ranging from micron scale fungi to large scale vertebrates, which possess unique adhesion characteristics, including self-cleaning, antifouling, and reusability in both wet and dry environments. Inspired from the natural adhesives, humans have endeavored to mimic and acquire those adhesion characteristics in artificially designed adhesives. Over several decades, researchers have employed various fabrication techniques and have used a variety of materials, predominantly polymers, to manufacture artificial adhesives which emulate the fundamental design aspects of the bioadhesion to match their adhesion performance. In this review, we briefly discuss the fundamentals aspects of adhesion, biomimetic design principles (derived from geckos, mussels, octopuses, and tree frogs), state of the art adhesion performance of the fabricated adhesives, their applications, and future outlook for the polymer-based adhesives both under dry and wet conditions.
Self-propelled Janus colloids (JCs) have recently gained much attention due to their ability to move autonomously and mimic biological microswimmers. This ability makes them suitable for prospective drug/cargo-delivery applications in microscopic domains. Understanding their dynamics in surroundings doped with macromolecules such as polymers is crucial, as most of the target application media are complex in nature. In this study, we investigate the selfdiffusiophoretic motion of hydrogen peroxide-fuelled SiO 2 −Pt JCs in the presence of dilute amounts of poly(ethylene oxide) (PEO). Despite the addition of PEO chains producing a Newtonian behavior with negligible increase in viscosity, the ballistic movement and rotational fluctuations of active JCs are observed to be significantly suppressed. With an increase in the polymer concentration, this leads to a transition from smooth to jittery to cage-hopping to the arrested motion of active JCs. We further propose that the anisotropic interaction of the polymers with the JC increases the "local drag" of the medium, resulting in the unusual impediment of the active motion.
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