(519a) Shear-Induced Alignment of Janus Particle Lamellar Structures

Authors: 
DeLaCruz-Araujo, R. A., University of Puerto Rico - Mayagüez
Beltran-Villegas, D. J., University of Michigan
Larson, R. G., University of Michigan
Córdova-Figueroa, U. M., University of Puerto Rico
Control over the alignment of colloidal structures plays a crucial role in advanced reconfigurable materials. In this work, we study the alignment of Janus particle lamellar structures under shear flow via Brownian dynamics simulations. Lamellar alignment (orientation relative to flow direction) is measured as a function of the particle volume fraction, strength of the anisotropic interaction potential, and the Péclet number (Pe)â??the ratio of viscous shear and Brownian forces. In conditions where lamellar structures are formed, three orientation regimes are observed: (1) Random orientation for Pe << 0.1, (2) parallel orientationâ??lamellae with their normals parallel to the direction of the velocity gradientâ??in the range of 0.1 < Pe < 10 and (3) perpendicular orientationâ??lamellae with their normals parallel to the vorticity directionâ??for Pe > 10. Our results suggest that the change of parallel to perpendicular orientation is caused by hydrodynamic torque on the particles overcoming Brownian rotary motion and torques resulting from interparticle interactions. We compare these results with analogous alignment obtained in smectic liquid crystalline and block copolymers under shear, in order to extend the implications of our study to other layer-forming fluids. This initial study of shear-induced alignment on lamellar structures formed by Janus colloidal particles also opens the door for future applications where a reversible actuator for structure orientation is required.