China’s Photocontrol of fluid slugs in liquid crystal polymer microactuatorsPosted: September 15, 2016
By Jiu-an Lv, Yuyun Liu, Jia Wei, Erqiang Chen, Lang Qin & Yanlei Yu of China’s Fudan University
The manipulation of small amounts of liquids has applications ranging from biomedical devices to liquid transfer. Direct light-driven manipulation of liquids, especially when triggered by light-induced capillary forces, is of particular interest because light can provide contactless spatial and temporal control. However, existing light-driven technologies suffer from an inherent limitation in that liquid motion is strongly resisted by the effect of contact-line pinning. Here we report a strategy to manipulate fluid slugs by photo-induced asymmetric deformation of tubular microactuators, which induces capillary forces for liquid propulsion. Microactuators with various shapes (straight, ‘Y’-shaped, serpentine and helical) are fabricated from a mechanically robust linear liquid crystal polymer. These microactuators are able to exert photocontrol of a wide diversity of liquids over a long distance with controllable velocity and direction, and hence to mix multiphase liquids, to combine liquids and even to make liquids run uphill. We anticipate that this photodeformable microactuator will find use in micro-reactors, in laboratory-on-a-chip settings and in micro-optomechanical systems.
Liquid droplets confined within a conical capillary tube — for instance in a microfluidic device — will travel spontaneously towards the narrower end, owing to differences in curvature pressure at either end of the droplet. Now, Yanlei Yu and colleagues have designed a tubular, light-actuated, liquid crystal polymer system that can induce such asymmetric morphologies to reversibly manipulate liquid drops through capillary forces. This method of light-controlled liquid movement does not suffer from contact-line pinning, and is shown to work with a range of liquids and mixtures to achieve propulsion with controllable velocity and direction, and mixing of multiphase liquids through microactuators of various shapes (straight, ‘Y’-shaped, serpentine and helical).
Source: Nature “Photocontrol of fluid slugs in liquid crystal polymer microactuators” (Nature 537, 179–184 (08 September 2016) doi:10.1038/nature19344 Received 07 December 2015 Accepted 20 July 2016 Published online 07 September 2016)