Department of Chemical Engineering, Indian Institute of Technology Guwahati , Guwahati, Assam 781039, India.
Centre for Nanotechnology, Indian Institute of Technology Guwahati , Guwahati, Assam 781039, India.
ACS Appl Mater Interfaces. 2017 Jan 11;9(1):1066-1076. doi: 10.1021/acsami.6b12182. Epub 2016 Dec 27.
Chemical pattern directed spin-dewetting of a macroscopic droplet composed of a dilute organic solution of liquid crystal (LC) formed an ordered array of micro- and nanoscale LC droplets. Controlled evaporation of the spin-dewetted droplets through vacuum drying could further miniaturize the size to the level of ∼90 nm. The size, periodicity, and spacing of these mesoscale droplets could be tuned with the variations in the initial loading of LC in the organic solution, the strength of the centripetal force on the droplet, and the duration of the evaporation. A simple theoretical model was developed to predict the spacing between the spin-dewetted droplets. The patterned LC droplets showed a reversible phase transition from nematic to isotropic and vice versa with the periodic exposure of a solvent vapor and its removal. A similar phase transition behavior was also observed with the periodic increase or reduction of temperature, suggesting their usefulness as vapor or temperature sensors. Interestingly, when the spin-dewetted droplets were confined between a pair of electrodes and an external electric field was applied, the droplets situated at the hydrophobic patches showed light-reflecting properties under the polarization microscopy highlighting their importance in the development of micro- or nanoscale LC displays. The digitized LC droplets, which were stationary otherwise, showed dielectrophoretic locomotion under the guidance of the external electric field beyond a threshold intensity of the field. Remarkably, the motion of these droplets could be restricted to the hydrophilic zones, which were confined between the hydrophobic patches of the chemically patterned surface. The findings could significantly contribute in the development of futuristic vapor or temperature sensors, light reflectors, and self-propellers using the micro- or nanoscale digitized LC droplets.
化学图案引导的宏观液滴的旋转去湿，该液滴由液晶（LC）的稀有机溶液组成，形成了微纳米级 LC 液滴的有序排列。通过真空干燥对旋转去湿液滴进行控制蒸发，可进一步将尺寸缩小到约 90nm 的水平。这些介观液滴的尺寸、周期性和间隔可以通过 LC 在有机溶液中的初始负载、液滴的向心力强度以及蒸发的持续时间的变化来调节。开发了一个简单的理论模型来预测旋转去湿液滴之间的间隔。图案化的 LC 液滴表现出从向列相到各向同性相的可逆相变，以及溶剂蒸气的周期性暴露和去除。随着周期性地增加或降低温度，也观察到类似的相变行为，这表明它们可用作蒸气或温度传感器。有趣的是，当旋转去湿液滴被限制在一对电极之间并且施加外部电场时，位于疏水区的液滴在偏振显微镜下表现出反射光的性质，突出了它们在微纳米级 LC 显示器发展中的重要性。否则处于静止状态的数字化 LC 液滴在超过电场强度阈值的情况下，在外电场的引导下表现出介电泳运动。值得注意的是，这些液滴的运动可以限制在亲水区域，该亲水区域被化学图案化表面的疏水区之间所限制。这些发现可以为使用微纳米级数字化 LC 液滴开发未来的蒸气或温度传感器、反光器和自推进器做出重大贡献。
