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Phase Separation of Nonionic Surfactant Aqueous Solution in Standing Surface Acoustic Wave for Submicron Particle Manipulation

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Abstract

Acoustic manipulation of submicron particles in a controlled manner has been challenging to date because of the increased contribution of acoustic streaming which leads to fluid mixing and homogenization. This article describes the patterning of submicron particles and the migration of their patterned locations from pressure nodes to antinodes in non-ionic surfactant (Tween 20) aqueous solution at a conventional standing surface acoustic wave field with the wavelength of 150 µm. Phase separation of the aqueous surfactant solution occurs when they are exposed to acoustic waves probably due to the “clouding behavior” of non-ionic surfactant. The generated surfactant precipitates are pushed to the pressure antinodes due to the negative acoustic contrast factor relative to water. Comparing with the mixing appearance in pure water media, acoustic radiation force dominant patterning behavior of submicron particles with a diameter of 300 nm is readily apparent in the aqueous solution with 2% volumetric concentration of Tween 20 surfactant, thanks to the suppression effect of acoustic streaming at inhomogeneous fluids. These submicron particles are first pushed to acoustic pressure nodes and then are migrated to antinodes where the surfactant precipitates stay. More attractively, the migration of acoustically patterned locations is not only limited to submicron particles and it also occurs to micrometer sized particles at solutions with higher surfactant concentrations. These findings open up a novel avenue for the controllable acoustic manipulation.
rsc.li/loc
Lab on a Chip
Devices and applications at the micro- and nanoscale
ISSN 1473-0197
Volume 21
Number 4
21 February 2021
Pages 619–786
COMMUNICATION
Pengfei Niu, Wei Pang et al.
Phase separation of a nonionic surfactant aqueous
solution in a standing surface acoustic wave for
submicron particle manipulation
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