Membrane-induced hydroelastic migration of a particle surfing its own wave. Issue 12 (December 2018)

• Record Type: Journal Article
• Authors: Rallabandi, Bhargav; Oppenheimer, Naomi; Ben Zion, Matan; Stone, Howard
• Is Part Of: Nature physics. Volume 14:Issue 12(2018)
• Page Start: 1211
• Page End: 1215
• Publication Date: 2018-12
• Subjects: Physics -- Periodicals; 530.05
• DOI: 10.1038/s41567-018-0272-z
• Languages: English
• ISSNs: 1745-2473

Abstract

Abstract While coupling between fluid flow and soft elastic surfaces is common in biology and engineering, an analytical description is challenging as it often involves non-linear dynamics. Here we show using theory and experiments that a small particle moving along an elastic membrane through a viscous fluid is repelled from the membrane due to hydroelastic forces. The flow field produces an elastic disturbance in the membrane leading to particle–wave coupling. We derive an analytic expression for the particle trajectory and find that the normal migration velocity of the particle is quadratic in its speed and depends on a combination of the tension and bending resistance of the membrane. Experimentally, we measure the normal displacement of spheres sedimenting under gravity along a suspended elastic membrane and find quantitative agreement with the theoretical predictions with no fitting parameters. We experimentally demonstrate that the effect is strong enough for separation and sorting of particles on the basis of both their size and density. We discuss the significance of our results for particles interacting with biological membranes, and propose the use of our model for membrane elasticity measurements. A rigid particle moving along a soft wall feels a repulsive force that can reduce its drag. Evidence now suggests that for thin enough walls the particle can be displaced appreciably—a finding that may have implications for biological membranes.