Related Experiment Video
Updated: May 8, 2026

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles
Published on: March 6, 2016
Attractive forces on hard and soft colloidal objects located close to the surface of an acoustic-thickness shear
Arne Langhoff1, Diethelm Johannsmann
1Institute of Physical Chemistry, Clausthal University of Technology, 38678 Clausthal-Zellerfeld, Germany.
Abstract:
Colloidal particles located close to the surface of an acoustic thickness shear resonator feel an attractive steady force, which is induced by the high-frequency tangential motion of the resonator surface. The range of the force is about half the penetration depth of the transverse viscous wave, that is, half of the thickness of the Stokes boundary layer. For an oscillation amplitude of 10 nm and a particle radius of 100 nm, the depth of attractive potential well corresponds to about 3 times the thermal energy, k(B)T. The force therefore suffices to overcome Brownian motion.
Related Concept Videos
Sound Waves: Resonance
Surface Tension, Capillary Action, and Viscosity
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
Concept of Resonance and its Characteristics
Van der Waals Interactions
Forced Oscillations
Standing Waves in a Cavity

