Nanoseminar 26 November - Shankar Kharal MSc (Rowan University)

Speaker: Shankar Kharal MSc (Rowan University)

Title: Centrifugal assembly of helical bijel fibers via microfluidic twisting 

Abstract: In microfluidics, centrifugal forces are important for centrifugal microfluidic chips and curved microchannels. Here, an unrecognized use of the centrifugal effect in microfluidics is introduced. We investigate the assembly of helical soft matter fibers in a rotating microcapillary. During assembly, the fibers undergo phase separation, generating particle stabilized bicontinuous emulsion gels (bijels).[1] This process is accompanied by a transition of the fiber density over time. As a result, the direction of the centrifugal force in the rotating microcapillary changes. We analyze this effect systematically with high-speed video microscopy and complementary computer simulations. The resulting understanding enables the control of the helical fiber assembly into microropes.[2] Such microropes have potentials for tissue engineering, additive manufacturing and catalysis. More generally, the knowledge gained from this work shows that centrifugal forces potentially enable directed self-assembly or separation of colloids, biological cells and emulsions in microfluidics.

[1] M. F. Haase, K. J. Stebe, D. Lee, Continuous Fabrication of Hierarchical and Asymmetric Bijel Microparticles, Fibers, and Membranes by Solvent Transfer-Induced Phase Separation (STRIPS). Adv. Mater. 27, 7065-7071 (2015).

[2] S. P. Kharal, R. P. Hesketh, M. F. Haase, High-Tensile Strength, Composite Bijels through Microfluidic Twisting. Adv. Funct. Mater. 30, 2003555(2020).