Speaker
Tapio Ala-Nissilä
(Aalto and Loughborough University)
Description
Controlled motion of micro and nanomotors in a fluid
environment is a promising tool in biology and biomedicine.
Fuel-free controlled propulsion and steering in aqueous
solutions have been experimentally demonstrated at the
microscale by taking advantage of the coupled rotational and
translational motion. The challenge in the controlled
propulsion and maneuverability at the nanoscale is
overcoming thermal effects which can alter the direction of
motion and interfere with the propulsion. The hybrid
lattice-Boltzmann -- Molecular Dynamics method with full
hydrodynamic interactions and thermal fluctuations [1] is
used to optimize the helical shapes and to demonstrate that
controlled propulsion and maneuverability is possible for
helically shaped structures at a sufficiently high Peclet
number, a ratio of the diffusive and propulsive timescales.
The magnetic helical structure interacts with a rotating
magnetic field. The interaction induces a torque that
propels the helix in the fluid through the coupled
rotational and translational motion. The Peclet number and
the propulsive velocity are quantified at various field
frequencies of the rotating magnetic field. The propulsive
velocities are observed to be linear with the field
frequencies up to a certain step-out frequency which depends
on the helical structures' rotational viscous drag
coefficient and the magnitude of the product of the magnetic
field strength and the magnetization of the helix. In the
presence of thermal fluctuations, we demonstrate that the
direction of motion of nanohelices may be altered and that
the helices can be guided to follow a pre-defined trajectory
[2].
[1] S.T. Ollila, C. Denniston, M. Karttunen, and T.
Ala-Nissila, J. Chem. Phys 134, 064902 (2011); Santtu T.T.
Ollila, Cristopher J. Smith, Tapio Ala-Nissila, and Colin
Denniston, Multiscale Modeling & Simulation 11, 213-243 (2013).
[2] M.M.T. Alcanzare, V. Thakore, M. Karttunen, S.T.T.
Ollila, and T. Ala-Nissila, Soft Matter 13, 2148 (2017);
M.M.T. Alcanzare, M. Karttunen, and T. Ala-Nissila, to
appear in Soft Matter (2019).
