A study on texture change on Langmuir monolayrs by optical tweezers

构建了布鲁斯特角显微镜与光镊的组合系统。在激光加热时，pentacosadiynoic酸Langmuir单层的分子取向的ε s=1点向错织构分裂成两个s=1/2缺陷。我们解释了这种行为的竞争的线张力的π壁的c-指向矢连接两个缺陷的连续取向的弹性能。虽然线张力引起的吸引力，取向弹性能介导的半整数向错之间的排斥相互作用。织构的激光加热局部地在取向有序的固相中诱导各向异性应力，迫使分子取向进入单层平面，并在那里通过降低π-壁线张力。用布鲁斯特角显微镜观察了二十五碳二炔酸单分子膜固相中连接半整数向错对的静态和动态弦缺陷织构。静态弦缺陷结构与四刷和双刷点向错共存。局部激光加热的使用已经允许人们观察在s=1点向错分裂成分数向错的分裂过程中连接两个半整数向错的弦缺陷的产生和湮灭的动力学。这些动力学已被分析，通过研究分子的取向弹性和线张力的字符串和向错的拖曳力之间的竞争。上述结果表明，光镊是研究固体朗缪尔单层膜微观操作和微观流变学的有力工具。

The combined system of Brewster angle microscope with optical tweezers has been constructed. Integer s=1 point disclination textures of the molecular orientation of a pentacosadiynoic acid Langmuir monolayr split into two s=1/2 defects upon laser heating. We explain this behavior by a competition of the line tension of a π-wall of the c-director connecting both defects with the continuum orientation elastic energy. While the line tension causes an attraction, the orientation elastic energy mediates a repulsive interaction between the half-integer disclinations. Laser heating of the texture locally induces an anisotropic stress in the orientationally ordered solid phase, forcing the molecular orientation into the monolayr plane and there by reducing the π-wall line tension. The static and dynamic string defect textures connecting pairs of half-integer disclinations have been observed by Brewster angle microscopy in the solid phase of pentacosadiynoic acid Langmuir monolayers. The static string defect structures have appeared coexisting with two kinds of point disclinations that have four and two black brushes. The use of local laser heating has allowed one to observe kinetics of creation and annihilation of string defects connecting the two-half-integer disclinations in the splitting process of an s=1 point disclination into fractional disclinations. These kinetics have been analyzed by studying the competition between the orientational elasticity of the molecules and the line tension of the string and the drag force of the disclinations. The above results demonstrate that optical tweezers are a powerful tool for the study of micromanipulations and microrheology in the solid Langmuir monolayrs.