Light-Driven Motion of Liquids on a Photoresponsive Surface

Abstract

The macroscopic motion of liquids on a flat solid surface was manipulated reversibly by photoirradiation of a photoisomerizable monolayer covering the surface. When a liquid droplet several millimeters in diameter was placed on a substrate surface modified with a calix[4]resorcinarene derivative having photochromic azobenzene units, asymmetrical photoirradiation caused a gradient in surface free energy due to the photoisomerization of surface azobenzenes, leading to the directional motion of the droplet. The direction and velocity of the motion were tunable by varying the direction and steepness of the gradient in light intensity. The light-driven motion of a fluid substance in a surface-modified glass tube suggests potential applicability to microscale chemical process systems.

Bifurcation of self-motion depending on the reaction order

“…Several artificial systems that exhibit self-motion under conditions of chemical nonequilibrium have been studied experimentally [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretically [16][17][18][19] under almost isothermal conditions.…”

Local Heating of Discrete Droplets Using Magnetic Porous Silicon-Based Photonic Crystals

“…Because each droplet can be independently controlled, highly integrated, scalable and flexible architectures can be implemented. 10 A number of techniques have been described for the actuation of droplets on solid surfaces including the use of thermocapillary effects, 14 photochemical effects, 15 electrochemical gradients, 16 surface tension gradients, 17 temperature gradients, 18 air pressure, 19 structured surfaces, 20 dielectrophoresis, 21 and electrostatic methods. 8 An extension of this approach is a liquid-liquid microfluidic system for manipulating freely suspended microliter or nanoliter droplets.…”

Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate

“…In the large majority of cases, the drop motion is induced by an interfacial energy gradient at a solid/liquid interface (wettability gradient) and/or at a free interface (Marangoni stress) 3. This has resulted in a plethora of studies to elucidate the fundamental mechanisms that convert such gradients into drop motion4 as well as to develop strategies to manipulate drops under the control of various external signals, such as thermal,5 electrical2, 6, 7 and optical8, 9, 10, 11, 12, 13 stimuli. Most of these approaches necessitate the implementation of rather complex components, such as electrodes or optical elements, or the development of systems that are intrinsically responsive to the desired stimulus, such as photo‐ or thermosensitive substrates 8, 9.…”

“…This has resulted in a plethora of studies to elucidate the fundamental mechanisms that convert such gradients into drop motion4 as well as to develop strategies to manipulate drops under the control of various external signals, such as thermal,5 electrical2, 6, 7 and optical8, 9, 10, 11, 12, 13 stimuli. Most of these approaches necessitate the implementation of rather complex components, such as electrodes or optical elements, or the development of systems that are intrinsically responsive to the desired stimulus, such as photo‐ or thermosensitive substrates 8, 9. This has led to the emergence of a broad variety of powerful drop actuation strategies that work in a laboratory environment, that is, require specific equipment and well‐controlled conditions (for example, protection from ambient light or precise control of temperature and surface tension).…”