Abstract
ABSTRACTA method to enable smectic A (SmA) liquid crystal (LC) devices to switch uniformly and hence fast from the clear state to a scattered state is presented. It will allow the reduction of the switching time for a SmA LC panel of 1 × 1 m2 changing from a clear state to a fully scattered state by more than three orders to a few tens of milliseconds. Experimental results presented here reveal that SmA LC scattering initiates from the nucleated LC defects at the field gradient of the applied electric field usually along the edges of the panel electrode and grows laterally to spread over a panel, which takes a long time if the panel size is large. By patterning the electrodes in use, it is possible to create a large number of field gradient sites near the electrode discontinuities, resulting in a uniform and fast switching over the whole panel and the higher the pattern density the shorter the panel switching time. For the SmA LC panels used here, the ITO transparent electrodes are patterned by laser ablation and photolithography. It is shown that the defect nucleation time is much shorter than the growth time of the scattered region, hence it is possible to use the density of the field gradient sites to control the uniformity and switching time of a panel. Furthermore, the patterned SmA panels have a lower switching voltage than that of the non-patterned ones in general.
Highlights
Large-size optically switching panels can enable a wide range of applications, from radiation control, ambient deco change to scattering media to information projection and display in the built environment both indoors and outdoors including privacy windows, building facades, and public information displays along motor ways and at transport hubs
This paper investigates the effect of the applied electric field on the scattering process and proposed a device structure with patterned electrodes for nearly size-independent fast and uniform scattering of smectic A (SmA) liquid crystal (LC) devices
Patterned electrodes prepared by the laser ablation process as described in Section 2.2 were made into devices with the organic Smectic A liquid crystal (SmA LC)
Summary
Large-size optically switching panels can enable a wide range of applications, from radiation control, ambient deco change to scattering media to information projection and display in the built environment both indoors and outdoors including privacy windows, building facades, and public information displays along motor ways and at transport hubs. State, resulting in a power consumption of ranging between 3.5 and 15.5 W/m2.[2] due to the nature of PDLC materials, there is a noticeable haze in the clear state of all the panels.[5] Another competing technology for liquid crystal (LC)-based smart window which should be mentioned is related to the so-called polymer stabilised cholesteric textures (PSCTs).[6,7] It has a bi-stable mode which can maintain either clear or low-transmittance state without a voltage supply. The scattering performances of organic and siloxane-based SmA LC devices are compared
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