Driving Droplets on Liquid Repellent Surfaces via Light‐Driven Marangoni Propulsion

Abstract

Marangoni flow, a surface shear flow, is a promising option for propulsion when controlling liquid droplet motion on solid substrates. However, the applicability of Marangoni flow induced by heating the substrate for droplet manipulation is limited by low precision of motion control and a narrow range of substrate types. Herein, a novel noncontact light-driven droplet manipulation method by using photothermally active droplets is introduced. Marangoni flow is induced by local photothermal heating via near-infrared (NIR) irradiation resulting in an internal flow that drives the droplets. The photothermally active droplets slide away from the NIR light and the direction of motion can be precisely controlled by changing the irradiation position remotely. In addition, it is demonstrated that the addition of a miscible liquid to the droplets can reverse the direction of motion. Moreover, the authors show that spherical droplets on conventional liquid repellent surfaces move through a rolling mechanism instead of sliding. It is believed that this droplet manipulation method can provide a general way of droplet transportation on solid surfaces.

Wetting Ridge‐Guided Directional Water Self‐Transport

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Light-driven mixing strategy inside a nanofluid droplet by asymmetrical Marangoni flow

“…This asymmetric effect acts on the immovable droplets; that is, the liquid medium has high wettability with the solid wall. Extending this method to nonwetting interfaces, such as smooth superhydrophobic surfaces, asymmetric flow within droplets can overcome the friction between the interfaces, resulting in noncontact optical drive translation or explaining the antigravity lifting effect of droplets (Hwang et al , 2022; Han et al , 2022). The numerical model of this paper has not considered this situation, which can be further studied in the follow-up research.…”

Liquid Film Sculpture via Droplet Impacting on Microstructured Heterowettable Surfaces

“…[ 1 ] Mastering the bionic strategies could direct the core design in diverse industrial applications, such as anti‐icing, [ 2 ] self‐cleaning, [ 3 ] and microfluidics, [ 4 ] and challenge the upcoming intelligent techniques including energy generation, [ 5 ] green printing, [ 6 ] and liquid robots. [ 7 ] Recent manipulation strategies are mainly divided into active method, by applying external electric fields, [ 8 ] magnetic fields, [ 9 ] temperature fields, [ 10 ] light, [ 11 ] and acoustic waves, [ 12 ] and passive method, by designing macrostructures like ridges, [ 13 ] tips, [ 14 ] ratchets, [ 15 ] grooves, [ 16 ] lattice cells, [ 17 ] or integrating wettable and less wettable regions on a solid surface. [ 18 ] Owing to its advantages of spontaneity, facility, diversity, as well as the energy‐saving property, the passive liquid manipulation method has aroused large amounts of research interest.…”