Umlandt Maren, Kopyshev Alexey, Pasechnik Sergey V, Zakharov Alexandre V, Lomadze Nino, Santer Svetlana
Institute of Physics and Astronomy, University of Potsdam, Potsdam14476, Germany.
Laboratory of Molecular Acoustics, MIREA-Russian Technological University, Moscow119454, Russia.
ACS Appl Mater Interfaces. 2022 Sep 14;14(36):41412-41420. doi: 10.1021/acsami.2c10710. Epub 2022 Aug 25.
Here, we establish different ways of light-triggered droplet manipulation such as reversible wetting, splitting, merging, and transport. The unique features of our approach are that the changes in the wetting properties of microscopic droplets of isotropic (oil) or anisotropic (liquid crystalline) liquids adsorbed on photoswitchable films can be triggered just by application of soft optical stimuli, which lead to dynamical, reversible changes in the local morphology of the structured surfaces. The adaptive films consist of an azobenzene-containing surfactant ionically attached to oppositely charged polymer chains. Under exposure to irradiation with light, the azobenzene photoisomerizes between two states, nonpolar -isomer and polar -isomer, resulting in the corresponding changes in the surface energy and orientation of the surfactant tails at the interface. Additionally, the local increase in the surface temperature due to absorption of light by the azobenzene groups enables diverse processes of manipulation of the adsorbed small droplets, such as the reversible increase of the droplet basal area up to 5 times, anisotropic wetting during irradiation with modulated light, and precise partition of the droplet into many small pieces, which can then be merged on demand to the desired number of larger droplets. Moreover, using a moving focused light spot, we experimentally demonstrate and theoretically explain the locomotion of the droplet over macroscopic distances with a velocity of up to 150 μm·s. Our findings could lead to the ultimate application of a programmable workbench for manipulating and operating an ensemble of droplets, just using simple and gentle optical stimuli.
在这里，我们建立了光触发液滴操纵的不同方式，如可逆润湿、分裂、合并和运输。我们方法的独特之处在于，仅通过施加柔和的光刺激，就能触发吸附在光开关薄膜上的各向同性（油）或各向异性（液晶）液体的微观液滴润湿特性的变化，这会导致结构化表面局部形态的动态、可逆变化。自适应薄膜由离子连接到带相反电荷的聚合物链上的含偶氮苯表面活性剂组成。在光照下，偶氮苯在非极性异构体和极性异构体两种状态之间发生光异构化，导致界面处表面能和表面活性剂尾部取向的相应变化。此外，由于偶氮苯基团吸收光导致表面温度局部升高，使得吸附的小液滴能够进行多种操纵过程，如液滴基底面积可逆增加高达5倍、在调制光照射期间的各向异性润湿，以及将液滴精确分割成许多小碎片，然后可根据需要合并成所需数量的较大液滴。此外，使用移动的聚焦光斑，我们通过实验证明并从理论上解释了液滴在宏观距离上以高达150μm·s的速度移动。我们的发现可能会导致最终应用一种可编程工作台，仅使用简单温和的光刺激就能操纵和操作一组液滴。
