液晶微流体中拓扑缺陷的形态研究

Morphology of topological defects in liquid crystal microfluidics

为了研究向列相液晶微流体在不同界面限制内拓扑缺陷的产生与演化,制备了不同表面锚定条件的微通道。通过采用不同表面特性的基板与聚二甲基硅氧烷制备的结构层键合,并合理利用氧等离子体对通道内壁化学特性的改变,最终制备出3种不同表面锚定条件的微流体通道。观察向列相液晶在其中的流动,总结了不同类型拓扑缺陷的出现规律。实验结果表明:平面取向的微通道内液晶分子排列连续,不会出现明显的缺陷结构。混合取向的微通道在界面锚定之间的竞争作用下,会在上表面附近形成稳定的相错线,相错线的数量与微通道的宽深比相关。正常情况下,垂直取向的微通道内指向场的变化具有良好的连续性,通过控制流速突变产生回流可以有效破坏微通道内指向场的连续性,从而产生动态的拓扑缺陷。缺陷的数量与流速相关。当流速恒定时,缺陷结构会维持短暂的动态平衡,随后会在通道内产生规律的波动。

In order to research the generation and evolution of topological defects in nematic liquid crystal microfluidics within different interfacial constraints,we prepared microchannels with different surface anchoring conditions.Three microchannels with varied surface anchoring conditions were created by bonding a substrate with different surface properties to a structural layer made of polydimethylsiloxane,and utilizing oxygen plasma to vary the chemical properties of the channel wall in a reasonable manner.The flow morphology of nematic liquid crystal in microchannels was examined,and the emergence regular of various forms of topological defect structures was summarized.Experimental results indicate that the liquid crystals in the planar alignment microchannel are arranged continuously without obvious defect structure.The hybrid alignment microchannel forms stable defect lines near the upper surface under the competition between interfacial anchors,and the number of defect lines is related to the breadth depth ratio of the microchannel.The director field in a homeotropic alignment microchannel shows excellent continuity under normal conditions.The backflow generated by controlled flow rate mutation can effectively disrupt the continuity of director field within the microchannel,thus creating dynamic topological defects.When the flow rate is constant,the defective structure maintains a brief dynamic equilibrium,followed by regular fluctuations in the channel.