Mechanism of Locomotion of Synthetic Nanomotors in a Viscous Fluid
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ATICAL PHYSICS
Mechanism of Locomotion of Synthetic Nanomotors in a Viscous Fluid S. I. Martynova,* and L. Yu. Tkacha,** a
Surgut State University, Surgut, 628412 Russia *e-mail: [email protected] **e-mail: [email protected]
Received November 18, 2019; revised November 18, 2019; accepted July 7, 2020
Abstract—A mechanism of nanomotor locomotion in a surrounding viscous fluid containing charged particles is considered. In contrast to a mechanism proposed in the literature, according to which nanomotor locomotion is induced by a concentration gradient of certain type particles produced by asymmetric chemical or electrochemical reactions occurring on the nanomotor surface, we hypothesize that nanomotor locomotion can be driven by hydrodynamic interactions in the case of identical concentrations of different-sized ions. To justify the hypothesis, the dynamics of a nanomotor surrounded by a viscous fluid is studied using the diffusion model of electrohydrodynamics and, additionally, the model of a dipolar aggregate surrounded by a cloud of equally but oppositely charged fine particles of different sizes is considered. It is assumed that the total charge of all fine particles is zero and the oppositely charged particles have identical concentrations in the ambient fluid. Computations have confirmed that the nanomotor can move in this case. The direction and speed of the motion depend substantially on both the distribution of the particles in the surrounding fluid and on their sizes. Symmetry breaking in the particle distribution gives rise to a velocity component perpendicular to the dipolar moment direction. In the case of the chemical or electrochemical mechanism of ion formation, symmetry breaking in the ion distribution can be caused by symmetry violations in the nanomotor shape or by possible impurities participating in the reaction, so, to control the nanomotor motion, an external field orienting the nanomotor in the prescribed direction has to be applied. The proposed mechanism of nanomotor locomotion can be used to control mass transfer in colloidal suspensions. Keywords: numerical simulation, viscous fluid, charged particles, self-electrophoresis, nanomotors, hydrodynamic interaction DOI: 10.1134/S0965542520110081
1. INTRODUCTION Modern scientific achievements in molecular biology and nanotechnologies provide the potential opportunity to design nanomechanical systems with various functional capabilities (hydrodynamic motors and pumps, microtools for inspecting vessels and organs in humans, etc.). Particularly worth noting are studies concerning biological and synthetic nanomotors (also known as microswimmers) [1, 2], which can find application as controlled vehicles for payload delivery in natural and laboratory conditions (e.g., to transport therapeutic payload and elements of self-assembling microdevices to targeted locations, etc.). At present, experiments have been conducted on the use of self-propelled microparticles for efficient removal of contaminants from water [3] and the use of nanorobots in me
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