Lee Kyung Min, Tohgha Urice, Bunning Timothy J, McConney Michael E, Godman Nicholas P
Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433, USA.
Azimuth Corporation, Fairborn, OH 45431, USA.
Nanomaterials (Basel). 2021 Dec 24;12(1):48. doi: 10.3390/nano12010048.
Blue phase liquid crystals (BPLCs) composed of double-twisted cholesteric helices are promising materials for use in next-generation displays, optical components, and photonics applications. However, BPLCs are only observed in a narrow temperature range of 0.5-3 °C and must be stabilized with a polymer network. Here, we report on controlling the phase behavior of BPLCs by varying the concentration of an amorphous crosslinker (pentaerythritol triacrylate (PETA)). LC mixtures without amorphous crosslinker display narrow phase transition temperatures from isotropic to the blue phase-II (BP-II), blue phase-I (BP-I), and cholesteric phases, but the addition of PETA stabilizes the BP-I phase. A PETA content above 3 wt% prevents the formation of the simple cubic BP-II phase and induces a direct transition from the isotropic to the BP-I phase. PETA widens the temperature window of BP-I from ~6.8 °C for BPLC without PETA to ~15 °C for BPLC with 4 wt% PETA. The BPLCs with 3 and 4 wt% PETA are stabilized using polymer networks via in situ photopolymerization. Polymer-stabilized BPLC with 3 wt% PETA showed switching between reflective to transparent states with response times of 400-500 μs when an AC field was applied, whereas the application of a DC field induced a large color change from green to red.
由双扭曲胆甾型螺旋结构组成的蓝相液晶(BPLCs)是下一代显示器、光学元件和光子学应用中很有前景的材料。然而,BPLCs仅在0.5 - 3°C的狭窄温度范围内被观察到,并且必须用聚合物网络来稳定。在此,我们报告通过改变无定形交联剂(季戊四醇三丙烯酸酯(PETA))的浓度来控制BPLCs的相行为。没有无定形交联剂的液晶混合物显示出从各向同性到蓝相-II(BP-II)、蓝相-I(BP-I)和胆甾相的狭窄相变温度,但添加PETA可稳定BP-I相。PETA含量高于3 wt%可防止简单立方BP-II相的形成,并诱导从各向同性到BP-I相的直接转变。PETA将BP-I的温度窗口从不含PETA的BPLC的约6.8°C拓宽到含4 wt% PETA的BPLC的约15°C。含3 wt%和4 wt% PETA的BPLCs通过原位光聚合使用聚合物网络进行稳定。含3 wt% PETA的聚合物稳定BPLC在施加交流电场时显示出反射态到透明态的切换,响应时间为400 - 500 μs,而施加直流电场会引起从绿色到红色的大颜色变化。