Colloidal particles (usually in the range of one nanometer to a couple of micrometers in size) with anisotropic properties at their surface are a contemporary subject of active research owing to their potential uses in the design of ‘smart’ materials, self-assembled and self-propelled devices, to mention a few. An attractive method for the fabrication of anisotropic particles is the use of microfluidics because of the benefit of obtaining a suspension of nearly uniform particle-size distribution (monodisperse colloidal suspension). Injection of two immiscible fluids containing monomers into a Y-type microfluidic generates a suspension of biphasic spherical drops, where each fluid phase that comprises the drop is bounded by a hemispherical domain, as shown in the figure below. This particular object is usually known in the literature as a Janus drop — named after the Roman god of two faces. After triggering the polymerization reaction the fluids solidify to form a particle with anisotropic properties.
Despite the use of microfluidics to synthesize anisotropic particles via the polymerization of a suspension of Janus drops, little is known about the behavior of Janus drops in external flows. An understanding of the behavior and dynamics of Janus drops is essential for the optimization of existing technologies and development of novel ones. A recent article in our research group sheds some light on some important aspects of the hydrodynamics of Janus drops subject to a linear shear flow:
Misael Díaz-Maldonado and Ubaldo M. Córdova-Figueroa (2015). On the anisotropic response of a Janus drop in a shearing viscous fluid. Journal of Fluid Mechanics, 770, R2 doi:10.1017/jfm.2015.148
For instance, the instantaneous force and torque on the Janus drop that arise by the action of a linear shear flow are characterized as a function of the orientation of the drop relative to the direction of the external flow. It is found that the Janus drop can behave as a single-phase drop or as a body with broken fore and aft symmetry depending on the orientation of the drop relative to the imposed flow. The dynamics of a freely suspended Janus drop in a shear flow are briefly discussed. And the resistance matrix introduced by H. Brenner is calculated for this interesting system.
The interested reader may download the article via the following link: