ABSTRACT
As a type of intelligent dimming film, polymer-dispersed liquid crystals (PDLCs) have been widely applied in various fields, such as smart windows, light shutters and displays. The properties of PDLCs are greatly influenced by the structure of the raw materials. In this work, the impact of crosslinking agents with different cyclic or chain groups was investigated by comparing the electro-optical performance and the morphology of the polymer matrix in the as-made PDLC films. It was found that the incorporation of large steric groups into the crosslinking agents can alter the morphology of the polymer matrix and thus affect the electro-optical properties. However, the impact is distinct when the spatial structure or rigidity is different. Besides, a combination of crosslinking agents with flexible alkyl-chain structures and steric structures can further reduce the threshold voltage while keeping the high contrast ratio. After detailed comparison, an optimized combination of BDDA/TCDDA in a weight ratio of 1/1 is selected to demonstrate the enhanced properties of the as-constructed film with a thickness of 20 µm. It exhibits low threshold voltage (8.2 V), low saturation voltage (21.2 V) and a high contrast ratio (203) simultaneously. This research offers an optimizing method from the crosslinking agent perspective and is anticipated to promote the further improvement of the PDLC's performance.
ABSTRACT
Polymer-dispersed liquid crystals (PDLCs) show great application potential in the areas of displays and smart windows. However, their electro-optical (E-O) properties such as contrast ratio and threshold voltage still need further improvement. In this study, the effects of α-substituted acrylate monomers on the morphology and E-O properties of PDLC composite films were systematically studied. It was found that the large substituent tended to increase the void size of the polymer matrix, while the small fluorine substitution led to a microsphere-type polymer morphology, which deteriorated the E-O performance. Finally, a largely improved E-O performance of low threshold voltage (0.437 V/µm), low saturation voltage (1.012 V/µm), and high contrast ratio (27) was achieved in an 8 µm-thick film by the addition of a chlorine-substituted monomer. This study provides a new approach for optimizing PDLCs from a material perspective.
ABSTRACT
This review addresses the latest situations and advances of near infrared spectroscopy (NIRS) in which detection of counterfeits and imitations, as well as monitoring origin and quality of Chinese crude drugs and Chinese patent medicines (CCDM) through consultation and summarization of relative literatures. On the one hand, NIRS gradually reveals its advantages and discriminating ability in the ways of nondestructive, rapid, simple, easy, and handy assessment. However NIRS still has some problems in representative samples and models stability for practice of CCDM. In order to keep up with popularization of NIRS in other areas, applications in detection of precious and/or priceless herbals, on-line quality control of valuable herbs, and screening of some chemicals illegally mixed into herbal preparations may be focused preferentially.
