Dynamics and Interactions of Colloidal Particles on Freely Suspended Smectic Films

自由悬浮近晶薄膜是一种独特的液体结构，厚度在几个分子层到几个微米之间，横向延伸可达几厘米。它们代表了易于准备的二维(2D)流体模型。在从三维到二维的过渡中，动力学的描述往往会简化，但也有定性的新现象。在某些情况下，二维液体中的动力学可能是相对复杂的(例如，斯托克斯悖论)。根据介相的不同，近晶薄膜在薄膜平面上可能是各向异性的(近晶C或近晶C*)或各向同性(近晶A)。我们研究了这类薄膜准2D几何结构中粒子的运动及其与周围导向场的相互作用。在之前的资助期间，发展了近晶薄膜中固体和液体夹杂物的制备，并借助偏光显微镜实验研究了固体微珠的运动。我们可以检验和验证Saffman-Delbrück模型对包裹体在二维流体中的迁移性，并观察到该模型的极限情况之间的转变。发展了一种将微滴射到近晶薄膜上的技术，并描述了这些微滴的影响、它们在薄膜中的掺入或通过薄膜的隧穿。定量观察和分析了环岛的聚结过程。二维各向同性形状记忆合金薄膜的研究结果现已发表。我们现在将重点关注各向异性SMC薄膜中的运动，并研究各向异性(形状各向异性)粒子。两个新的有趣的方面是各向异性二维流体中剪切粘度和旋转粘度的结合，以及棒状包裹体的重取向动力学。对于这两个主题，都有定性的初步研究，但申请者小组和其他研究小组到目前为止都没有获得实验结果。我们计划进行定量实验和数值(有限元)模拟。它们将构成对准2D各向异性流体中流体动力学过程的系统描述的基础。

Freely suspended smectic films are unique liquid structures with thicknesses between a few molecular layers and a few microns, with lateral extensions up to several centimeters. They represent easily prepared models of two-dimensional (2D) fluids. In the transition from three to two dimensions, the description of the dynamics often simplifies, but there are also qualitatively new phenomena. Under certain circumstances, the dynamics in a two-dimensional liquid can be relatively complicated (see, e.g. the Stokes paradox).Depending on the mesophase, smectic films may be anisotropic (smectic C or smectic C*) or isotropic (smectic A) in the film plane. We study the motion of particles in the quasi-2D geometry of such films, and their interactions with the surrounding director field.In the previous funding period, the preparation of solid and liquid inclusions in smectic films was developed and the motion of solid beads was studied with the aid of polarized light microscopy experiments. We could test and verify the Saffman-Delbrück model for the mobility of inclusions in 2D fluids and the transition between the limiting cases of the model was observed. A technique to shoot microdroplets onto smectic films was developed, and the impact of these droplets, their incorporation into the films or the tunneling through the films were described. Coalescence prozesses of circular islands were observed and analyzed quantitatively. The findings for 2D isotropic SmA films have now been published. We will now focus on the motion in anisotropic SmC films, and investigate anisometric (shape anisotropic) particles. Two new and interesting aspects are the incorporation of the set of shear viscosities and the rotational viscosity in anisotropic 2D fluids, as well as the reorientation dynamics of rod-shaped inclusions.For both topics, there are qualitative preliminary studies, but neither the group of the applicant nor other research groups so far have obtained experimental results. We plan both quantitative experiments and numerical (FEM) simulations. They will form the basis of a systematic description of hydrodynamic processes in quasi-2D anisotropic fluids.