A review of shaped colloidal particles in fluids: Anisotropy and chirality
10 Sep 2020
•
Witten Thomas A.
•
Diamant Haim
This review treats asymmetric colloidal particles moving through their host
fluid under the action of some form of propulsion. The propulsion can come from
an external body force or from external shear flow...It may also come from
externally-induced stresses at the surface, arising from imposed chemical,
thermal or electrical gradients. The resulting motion arises jointly from the
driven particle and the displaced fluid. If the objects are asymmetric, every
aspect of their motion and interaction depends on the orientation of the
objects. This orientation in turn changes in response to the driving. The
objects' shape can thus lead to a range of emergent anisotropic and chiral
motion not possible with isotropic spherical particles. We first consider what
aspects of a body's asymmetry can affect its drift through a fluid, especially
chiral motion. We next discuss driving by injecting external force or torque
into the particles. Then we consider driving without injecting force or torque. This includes driving by shear flow and driving by surface stresses, such as
electrophoresis. We consider how time-dependent driving can induce collective
orientational order and coherent motion. We show how a given particle shape can
be represented using an assembly of point forces called a Stokeslet object. We
next consider the interactions between anisotropic propelled particles, the
symmetries governing the interactions, and the possibility of bound pairs of
particles. Finally we show how the collective hydrodynamics of a suspension can
be qualitatively altered by the particles' shapes. The asymmetric responses
discussed here are broadly relevant also for swimming propulsion of active
micron-scale objects such as microorganisms.(read more)