30 research outputs found
Hydrodynamic interactions in dense active suspensions: from polar order to dynamical clusters
We study the role of hydrodynamic interactions in the collective behaviour of
collections of microscopic active particles suspended in a fluid. We introduce
a novel calculational framework that allows us to separate the different
contributions to their collective dynamics from hydrodynamic interactions on
different length scales. Hence we are able to systematically show that
lubrication forces when the particles are very close to each other play as
important a role as long-range hydrodynamic interactions in determining their
many-body behaviour. We find that motility-induced phase separation is
suppressed by near-field interactions, leading to open gel-like clusters rather
than dense clusters. Interestingly, we find a globally polar ordered phase
appears for neutral swimmers with no force dipole that is enhanced by near
field lubrication forces in which the collision process rather than long-range
interaction dominates the alignment mechanism.Comment: 7 pages, 4 figure
Self-propelled motion of a fluid droplet under chemical reaction
We study self-propelled dynamics of a droplet due to a Marangoni effect and
chemical reactions in a binary fluid with a dilute third component of chemical
product which affects the interfacial energy of a droplet. The equation for the
migration velocity of the center of mass of a droplet is derived in the limit
of an infinitesimally thin inter- face. We found that there is a bifurcation
from a motionless state to a propagating state of droplet by changing the
strength of the Marangoni effect.Comment: 19 pages, 4 figure
Active Motion of Janus Particle by Self-thermophoresis in Defocused Laser Beam
We study self-propulsion of a half-metal coated colloidal particle under
laser irradiation. The motion is caused by self-thermophoresis: i.e. absorption
of laser at the metal-coated side of the particle creates local temperature
gradient which in turn drives the particle by thermophoresis. To clarify the
mechanism, temperature distribution and a thermal slip flow field around a
micro-scale Janus particle are measured for the first time. With measured
temperature drop across the particle, the speed of self-propulsion is
corroborated with the prediction based on accessible parameters. As an
application for driving micro-machine, a micro-rotor heat engine is
demonstrated