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Sungyon Lee: Probing the intersection of fluid and solid with suspensions

Scientific image of Seed project

Fig. 1: When the suspension (of polyethylene particles and silicone oil) is injected into an air-filled 2D channel, particles accumulate on the suspension-air interface to form a band nearing the maximum packing fraction. The band subsequently breaks, leading to pattern formations in the suspension. [2]

[1] I.B. Liu, G. Bigazzi, N. Sharifi-Mood, L. Yao, and K. J. Stebe, “Curvature capillary repulsion,” Phys. Rev. Fluids 2, 100501 (2017).
[2] J. Kim, F. Xu and S. Lee, “Formation and destabilization of the particle band on the fluid-fluid interface,” Phys. Rev. Lett. 118, 074501 (2017).

Suspensions, consisting of solid particles dispersed in a liquid, form the basis of many complex fluids and tunable materials that sit at the intersection between fluid and solid. It is commonly understood that fluid-like suspensions jam and solidify when the particle volume fraction or the geometric confinement is increased beyond a critical point. However, this simple “static” picture does not capture the rich dynamic response of dense suspensions in flow. Recently, a dynamic transition from fluid to solid in suspensions has enabled the development of flexible spacesuits for astronauts and new materials that enhance vehicle traction. Hence, understanding the complex response of suspensions to different dynamic conditions is fundamentally important and warrants further investigation.

In this project, we focus on the dynamics and spontaneous pattern formation in suspensions in a Hele-Shaw cell, specifically in the presence of the fluid-fluid interface. Recent studies have shown that fluid interfaces work as a site onto which particles can adsorb and form new 2D structures [1]; the resultant particle-laden interfaces are then rigid and solid-like. At the same time, under certain flow conditions, particles can cluster and form patterns in the bulk suspension (see Figure 1). Based on this dual effect of particles to destabilize the bulk suspension but to stabilize the interface, we will experimentally demonstrate the use of suspended particles to (a) rigidify the fluid-fluid interface and, in turn, to (b) alter the pattern formation in dense suspensions. In so doing we aim to control suspension processing, and even discover ways to generate new structures in suspensions and on the fluid interface.

Funded by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013

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