Beijing National Laboratory for Molecular Science (BNLMS), Center for Molecular Science, Institute of Chemistry, University of Chinese Academy of Sciences , Beijing 100190, P. R. China.
Acc Chem Res. 2014 Aug 19;47(8):2342-52. doi: 10.1021/ar5000693. Epub 2014 Jul 14.
One-dimensional materials (1D) capable of transporting liquid droplets directionally, such as spider silks and cactus spines, have recently been gathering scientists' attention due to their potential applications in microfluidics, textile dyeing, filtration, and smog removal. This remarkable property comes from the arrangement of the micro- and nanostructures on these organisms' surfaces, which have inspired chemists to develop methods to prepare surfaces with similar directional liquid transport ability. In this Account, we report our recent progress in understanding how this directional transport works, as well our advances in the design and fabrication of bioinspired 1D materials capable of transporting liquid droplets directionally. To begin, we first discuss some basic theories on droplet directional movement. Then, we discuss the mechanism of directional transport of water droplets on natural spider silks. Upon contact with water droplets, the spider silk undergoes what is known as a wet-rebuilt, which forms periodic spindle-knots and joints. We found that the resulting gradient of Laplace pressure and surface free energy between the spindle-knots and joints account for the cooperative driving forces to transport water droplets directionally. Next, we discuss the directional transport of water droplets on desert cactus. The integration of multilevel structures of the cactus and the resulting integration of multiple functions together allow the cactus spine to transport water droplets continuously from tip to base. Based on our studies of natural spider silks and cactus spines, we have prepared a series of artificial spider silks (A-SSs) and artificial cactus spines (A-CSs) with various methods. By changing the surface roughness and chemical compositions of the artificial spider silks' spindle-knots, or by introducing stimulus-responsive molecules, such as thermal-responsive and photoresponsive molecules, onto the spindle-knots, we can reversibly manipulate the direction of water droplet's movement on the prepared A-SSs. In addition, the A-SSs with nonuniform spindle-knots, such as multilevel sized spindle-knots and gradient spindle-knots, further demonstrate integrated directional transport ability for water droplets. Through mimicking the main principle of cactus spines in transporting water droplets, we were able to fabricate both single and array A-CSs, which are able to transport liquid droplets directionally both in air and under water. Lastly, we demonstrated some applications of this directional liquid transport, from aspects of efficient fog collection to oil/water separation. In addition, we showed some potential applications in smart catalysis, tracer substance enrichment, smog removal, and drug delivery.
一维材料（1D）能够定向输送液滴，例如蜘蛛丝和仙人掌刺，由于其在微流控、纺织品染色、过滤和烟雾去除等领域的潜在应用，最近引起了科学家的关注。这种显著的特性来自于这些生物体表面微纳结构的排列，这启发了化学家开发出制备具有类似定向液体传输能力的表面的方法。在本报告中，我们报告了我们在理解这种定向传输如何工作以及设计和制造能够定向输送液滴的仿生 1D 材料方面的最新进展。首先，我们先讨论一些关于液滴定向运动的基本理论。然后，我们讨论了在天然蜘蛛丝上定向传输水滴的机制。当与水滴接触时，蜘蛛丝经历了所谓的湿重构，形成了周期性的纺锤结和关节。我们发现，纺锤结和关节之间的拉普拉斯压力和表面自由能梯度是导致水滴定向传输的协同驱动力。接下来，我们讨论了在沙漠仙人掌上定向传输水滴的机制。仙人掌的多层次结构的集成和多种功能的集成使得仙人掌刺能够连续地将水滴从尖端输送到底部。基于我们对天然蜘蛛丝和仙人掌刺的研究，我们已经使用各种方法制备了一系列人工蜘蛛丝（A-SSs）和人工仙人掌刺（A-CSs）。通过改变人工蜘蛛丝纺锤结的表面粗糙度和化学成分，或者在纺锤结上引入热响应和光响应分子等刺激响应分子，我们可以可逆地操纵制备的 A-SSs 上水滴的运动方向。此外，具有非均匀纺锤结的 A-SSs，例如多级尺寸的纺锤结和梯度纺锤结，进一步展示了水滴的集成定向传输能力。通过模拟仙人掌刺输送水滴的主要原理，我们能够制造出单根和阵列的 A-CSs，它们能够在空气和水下都定向输送液滴。最后，我们从高效雾收集到油水分离等方面展示了这种定向液体传输的一些应用。此外，我们还展示了在智能催化、示踪物质富集、烟雾去除和药物输送等方面的一些潜在应用。
