Improved electro-optical and dielectric properties of polymer dispersed liquid crystal doped with disperse dye red 1 and carbon nanoparticles

Disperse dye red 1 (DR1) and carbon nanoparticles (CNPs) were doped separately to form polymer dispersed liquid crystal films, namely, DPDLC & CPDLC. Nematic liquid crystal (LC) and photopolymer NOA-65 were used to prepare these composite films using polymerisation-induced phase separation (PIPS) technique. In this research work, it is demonstrated that the minute concentration (0.05% wt./wt.) of DR1 and CNPs controls the LC droplet alignment and LC droplet size in polymer dispersed liquid crystal (PDLC) film. The effect of DR1 and CNPs on PDLC film has been investigated in terms of LC droplet size, transition temperature, voltage-transmittance characteristic, contrast ratio, response time, haze, and dielectric measurements. The obtained results reveal that the threshold voltage values of the composite film get reduced from 34.87 V (undoped) to 10.19 and 9.26 V, for 0.05% of DR1 and CNPs doping, respectively. The DR1 (0.05%) doped film shows improved contrast of the undoped film as compared to CNPs (0.05%) film, whereas CNPs (0.05%) doped film shows a faster response time of 2.81 ms as compared to DR1 (0.05%) doped film (3.14 ms). Dielectric analysis of undoped, DPDLC, and CPDLC films represents Debye type relaxation mode.将分散红1染料（Disperse dye red 1, DR1）与碳纳米颗粒（carbon nanoparticles, CNPs）分别掺杂，制备得到两类聚合物分散液晶薄膜，分别记为DPDLC与CPDLC。本研究采用聚合诱导相分离法（polymerisation-induced phase separation, PIPS），以向列相液晶（nematic liquid crystal, LC）与光敏聚合物NOA-65为原料制备上述复合薄膜。研究证实，质量分数为0.05%的DR1与CNPs即可调控聚合物分散液晶（PDLC）薄膜内的液晶液滴取向与液滴尺寸。本文从液晶液滴尺寸、相变温度、电压-透过率特性、对比度、响应时间、雾度以及介电性能测试等维度，探究了DR1与CNPs掺杂对PDLC薄膜性能的影响。测试结果表明：未掺杂的原始PDLC薄膜阈值电压为34.87 V，经0.05% DR1与CNPs掺杂后，阈值电压分别降至10.19 V与9.26 V。0.05% DR1掺杂薄膜的对比度优于未掺杂样品，且相较于0.05% CNPs掺杂薄膜，其对比度表现更优异；而0.05% CNPs掺杂薄膜的响应速度更快，响应时间仅为2.81 ms，相较之下0.05% DR1掺杂薄膜的响应时间为3.14 ms。对未掺杂、DPDLC及CPDLC薄膜的介电分析显示，三者的介电弛豫均呈现德拜型弛豫模式。