The large-area formation of functional micropatterns with liquid crystals is of great significance for diversified applications in interdisciplinary fields. Meanwhile, the control of molecular alignment in the patterns is fundamental and prerequisite for the adequate exploitation of their photoelectric properties. However, it would be extremely complicated and challenging for discotic liquid crystals (DLCs) to achieve the goal, because they are insensitive to external fields and surface chemistry. Herein, a simple method of patterning and aligning DLCs on flat substrates is disclosed through precise control of the formation and dewetting of the capillary liquid bridges, within which the DLC molecules are confined. Large-area uniform alignment occurs spontaneously due to directional shearing force when the solvent is slowly evaporated and programmable patterns could be directly generated on desired substrates. Moreover, the in-plane column direction of DLCs is tunable by slightly tailoring their chemical structures which changes their self-assembly behaviors in liquid bridges. The patterned DLCs show molecular orientation-dependent charge transport properties and are promising for templating self-assembly of other materials. The study provides a facile method for manipulation of the macroscopic patterns and microscopic molecular orientation which opens up new opportunities for electronic applications of DLCs.
A microfluidic system is designed to fabricate polymer dispersed liquid crystal microspheres, whose shape, surface smoothness, and size are controlled. A microlens array (MLA) is constructed by the assembly of the monodispersed microspheres. In the MLA, each microsphere acts as a separate imaging unit. As the liquid crystal (LC) used is a mixed liquid crystal that contain photoresponsive 4‐butyl‐4‐methoxyazobenzene, the imaging capability and light transportation of the MLA can be reversibly controlled by light irradiation.
A microfluidic design was created to allow liquid microlens to control focal length and light transmission. The focal length of the microlens was controlled by varying the volume of liquid infused into the liquid cell. The cell extruded a polydimethylsiloxane film and produced a changeable curvature. The imaging ability of the microlens was tuned by taking advantage of the phase transition of poly-N-isopropylacrylamide in the liquid. The phase transition temperature was controlled in the range of 25.6–34.5°C by changing the ion concentration.
The preparation of regular microstructures with liquid crystalline materials for organic field effect transistors (OFETs) is an attractive but challenging issue. However, it is usually limited by the difficulty of forming large-area single crystals aligned in a desirable direction. Herein, several terthiophene (TTP) smectic liquid crystals such as 8-TTP-8 and 12-TTP-11OH are patterned into highly crystalline microstripes by a sandwich system through a dewetting method. Morphology and orientation of the microstripes strongly depend on preparation temperature. Microstripes prepared below crystalline temperature are uniform, well-ordered, and show high field effect transistor (FET) mobility. Meanwhile, π-π stacking direction of the TTP backbone is perpendicular to the microstripe and the molecules stack in layer structure, standing up on the SiO 2 /Si substrate, which would provide an effective pathway for p-type charge transport. However, higher preparation temperatures at liquid crystalline or isotropic liquid range induce many defects in the crystal formation process and cause incline of the unit cell, thus leading to a sharp decrease in FET mobility. A possible mechanism of molecular stacking at different temperature range is proposed. This strategy promised to provide a new opportunity for the high cost-efficiency fabrication of OFETs.
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