Light induced manipulation of isotropic and anisotropic liquids absorbed on photosensitive surfaces

我们的建议的总体目标是研究液滴的行为，包括各向同性或各向异性（液晶）的光可切换的聚合物基板上的液体，其润湿性能可以改变本地，动态和可逆地响应于合适的光学刺激。从长远来看，我们将创建一个适应性强的平台，在这个平台上可以建立对吸附液滴的基本操作，如合并，分裂，混合或运输。光敏基底由含偶氮苯的聚合物组成。仅需要温和的照射来触发形貌和表面能的显著变化。众所周知，当用光学干涉图案照射含偶氮苯的聚合物膜时，膜形貌急剧变化以形成表面浮雕光栅：在最简单的情况下，形貌模仿强度分布并变形成波状正弦方式，其幅度可以与总膜厚度相当。这一过程发生在玻璃态，没有软化。我们以前已经表明，这些光栅可以出现或消失，甚至“设置在运动中”，也就是说，通过利用两个干涉光束中的重复偏振变化，可以像涟漪一样移动。在当前的项目中，我们将介绍两个新的方面的功能化表面与切换润湿性能的研究。首先，被吸附的液滴将被操纵的有限的，不同的润湿性的异质图案，这些变化是完全可逆的，使系统可重构。第二，润湿性发生变化的动力学将被明确考虑。我们的系统固有的有两个时间尺度：表面能量预计几乎是瞬间变化的，但纹理和地形的演变将需要更长的时间。这些后面的方面可以显著影响如何定义方便的照射方案以实现对液滴的快速操作，另外还受到其他条件的影响，例如偶氮苯分子、聚合物的性质和聚合物变形的程度。

The general goal of our proposal is to study the behavior of droplets, consisting of isotropic or anisotropic (liquid crystalline) liquids on photo-switchable polymer substrates, the wetting properties of which can be changed locally, dynamically and reversibly in response to suitable optical stimuli. In the long run, we shall create an adaptable platform on which elementary operations on adsorbed liquid droplets such as merging, splitting, mixing or transport can be established. The photosensitive substrate consists of azobenzene containing polymers. Only gentle irradiation is needed to trigger significant changes in topography and surface energy. It is well known that when azobenzene containing polymer films are irradiated with optical interference patterns the film topography changes drastically to form surface relief gratings: in the simplest case, the topography mimics the intensity distribution and deforms into a wave-like, sinusoidal manner, the amplitude of which may be comparable to the total film thickness. This process takes places in the glassy state without softening. We have previously shown that these gratings can be made to appear or disappear or even “set in motion”, that is, be made to move like ripples across water by exploiting repetitive polarization changes in the two interfering beams. With the current project, we shall introduce two new aspects to the study of functionalized surfaces with switchable wetting properties. First, adsorbed liquid droplets will be manipulated by finite, heterogeneous patterns of varying wettability; these changes are completely reversible rendering the system reconfigurable. Second, the dynamics by which changes in wettability occur will be considered explicitly. Inherent to our systems there are two time scales: surface energies are expected to change almost instantaneously, but the evolving changes in texture and topography will take significantly longer. These latter aspects may significantly influence how a convenient irradiation protocol may be defined to achieve swift operations on a droplet, additionally impacted by other conditions, such as nature of azobenzene molecule, polymer and the extent of polymer deformation.