Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate
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DOI：
10.1039/c9ra02552a
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发表时间：
2019-07-16
期刊：
影响因子：
3.9
通讯作者：
Mukherjee, Rabibrata
中科院分区：
文献类型：
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作者：
Dhara, Palash;Mukherjee, Rabibrata
我们报道了涂覆在具有不同线宽（l(P)）和周期性（lambda(P)）的光栅几何形状的平面和地形图案衬底上的5CB液晶（LC）薄膜的热诱导向列相到各向同性（N-I）相变以及脱湿。在平面衬底上，发生在31.1℃至34.4℃温度范围内的向列相到各向同性（N-I）相转变是完全可逆的，当样品在各向同性到向列相（I-N）转变期间冷却时，会重新出现相同的纹影织构。在进一步加热超过N-I转变和在约65℃下退火后，薄膜经历成核脱湿，形成和生长孔洞，最终合并形成孤立的液滴。当薄膜从这一阶段冷却到室温时，脱湿结构的形态保持不变，尽管这些特征经历了向列相状态的相变。与此相反，在有地形图案的衬底上，相变周期与冷却到向列相阶段期间薄膜质地的变化有关。有趣的是，当λ (P)接近1.5 μ m时，分子表现出各向同性锚定，当λ (P)很大（接近10 μ m）时，分子表现出平面锚定。当进一步加热到约65摄氏度时，薄膜在地形图案衬底上脱落，导致液滴的收集，当λ (P)很大（约10 μ m）时，液滴与衬底图案对齐。相反，当λ (P)较低（约为1.5 μ m）时，脱湿液滴是随机的，与模式无关。
We report thermally induced nematic to isotropic (N-I) phase transition as well as dewetting of 5CB Liquid Crystal (LC) thin films coated on flat and topographically patterned substrates with grating geometry of different line width (l(P)) and periodicity (lambda(P)). On a flat substrate, the nematic to isotropic (N-I) phase transition, which takes place within a temperature range between 31.1 degrees C and 34.4 degrees C is fully reversible, with re-appearance of identical Schlieren texture when the sample is cooled down during isotropic to nematic (I-N) transition. Upon further heating beyond N-I transition and annealing at T approximate to 65 degrees C, the film undergoes nucleated dewetting with formation and growth of holes, which eventually merge to form isolated droplets. The morphology of the dewetted structures remains unaltered when the film is cooled to room temperature from this stage, though the features undergo phase transition to the nematic state. In contrast on a topographically patterned substrate, the phase transition cycle is associated with a change of the texture of the film during cooling to the nematic stage. Interestingly the molecules exhibit homeotropic anchoring when lambda(P) approximate to 1.5 mu m and planar anchoring when lambda(P) large (approximate to 10 mu m). When heated further to T approximate to 65 degrees C, the film dewets on topographically patterned substrates resulting in a collection of droplets, which are aligned to the substrate patterns when lambda(P) is large (approximate to 10 mu m). In contrast the dewetted droplets are random and not correlated to the patterns when lambda(P) is lower (approximate to 1.5 mu m).