J. William Doane

Response times and voltages for PDLC light shutters

Abstract The response times and operating voltages of light shutters formed from polymer dispersed liquid crystals (PDLCs) have been studied experimentally and the results compared with calculations based on non-sperhically shaped nematic droplet models. The experiments were performed on light shutters with elongated and uniformly aligned droplets where the relaxation time and voltage response were measured. It is shown that the droplet shape can be a dominant factor, particularly for the relaxation time, and the data are compared with equations derived in terms of the aspect ratio of the droplet l = a/b, where a and b are the lengths of the semi-major and semi-minor axes, respectively, of the elongated droplet. It is further demonstrated that the electric field inside the droplet can be considerably smaller than the applied field, due to the conductivity and dielectric properties of the polymer and liquid crystal materials. These data are used to obtain values for the ratio of the conductivities of the p...

Microscope textures of nematic droplets in polymer dispersed liquid crystals

Computer simulations are made of polarizing microscope textures of supramicron‐sized nematic droplets with director configurations which commonly occur in polymer and other dispersions. The simulations are computed from polarization rotations and phase shifts caused by nonuniform optical anisotropies of the nematic structure in liquid crystal droplets. The treatment is limited to the case of spherical droplets which are optically soft so that reflection and refraction at the droplet surface, as well as refraction on any internal structure, can be neglected. Simulated polarizing microscope textures of four different director configurations at different orientations are presented graphically. The simulated pictures are shown to compare well with observations of actual nematic droplets viewed under crossed polars.

50.1: Distinguished Contributed Paper: Single Substrate Encapsulated Cholesteric LCDs: Coatable, Drapable and Foldable

We have developed the first ever reflective cholesteric liquid crystal displays on single textile substrates made with simple coating processes. This paper reports on a novel approach for fabrication of ultra-thin encapsulated cholesteric liquid crystal displays with transparent conducting polymers as bottom and top electrodes. These displays are fabricated from bottom-up by sequential coating of various functional layers on fabric materials. Encapsulation of the cholesteric liquid crystal droplets in polymer matrix and mechanical flexibility of the conducting polymers allow us to create durable and highly conformable textile displays. We discuss the development and status of this next generation display technology for both monochrome and multi-color cholesteric displays.

50.4: Flexible Encapsulated Cholesteric LCDs by Polymerization Induced Phase Separation

We demonstrate a cholesteric liquid crystal-polymer dispersion where the liquid crystal is encapsulated via polymerization induced phase separation. A polymerizable additive formulation is used to control the liquid crystal droplet size. Encapsulation prevents the flow of liquid crystal thereby preserving the bistable texture when the display is flexed.

Transient Dielectric Study of Bistable Reflective Cholesteric Displays and Design of Rapid Drive Scheme

Transient dielectric measurement is used to study the transitions among the planar, focal conic, and homeotropic states of cholesteric liquid crystals. If the initial state is the field‐induced homeotropic state, at low bias fields, the liquid crystal transforms to the planar state in a sequence of homeotropic‐transient planar–planar; at high bias fields, the liquid crystal transforms to the focal conic state. The homeotropic‐transient planar transition is on the order of 1 ms while the homeotropic‐focal conic transition is on the order of 100 ms. Large hysteresis is observed in the transitions between the homeotropic and the focal conic state. Based on the rapid homeotropic‐transient planar transition and the hysteresis effect in the focal conic‐homeotropic transition, we have designed a drive scheme which can address bistable reflective cholesteric displays at the speed of one line per millisecond.

Thin flexible photosensitive cholesteric displays

— A novel optically addressable, flexible bistable cholesteric liquid-crystal display (ChLCD) is presented. These displays utilizeazo-binaphthalene photosensitive chiral dopants that undergo photo-isomerization upon exposure to light. The isomerization results in a change in the pitch of the cholesteric liquid crystal (ChLC), which enables the creation of inherently high-resolution light-weight displays that are optically written. The displays can be photo-addressed without patterned electrodes or complex addressing schemes. Capitalizing on the dynamic pitch and the bistability of photosensitive ChLCDs, the display is switched with a single pulse at a specific single voltage to drive the region of the display with a shorter pitch to the focal-conic texture and the region of the display with a longer pitch to the planar texture. Once in the different textures, the display can hold an image indefinitely regardless of ambient lighting. As such, these displays are a natural fit for badges, shelf-labels, and point-of-sale cards. In this paper, the photosensitive properties of an encapsulated display system in comparison to an unencapsulated display system is discussed. Properties such a photosensitivity, thermal relaxation, and electro-optical response are studied and reported. In addition, a flexible optically addressable ChLCD is developed and demonstrated.

Single‐substrate encapsulated cholesteric LCDs: Coatable, drapable, and foldable

— The first ever, reflective cholesteric liquid-crystal displays (ChLCDs) on single textile substrates made with simple coating processes have been developed. A novel approach for fabrication of ultra-thin encapsulated ChLCDs with transparent conducting polymers as bottom and top electrodes will be reported. These displays are fabricated from the bottom-up by sequential coating of various functional layers on fabric materials. Encapsulation of the cholesteric liquid-crystal droplets in a polymer matrix and the mechanical flexibility of the conducting polymers allow for the creation of durable and highly conformable textile displays. The development and status of this next-generation display technology for both monochrome and multicolor cholesteric displays will be discussed.

PDLC shutters: where has this technology gone?

A Commentary on the paper ”Response times and voltages for PDLC shutters„, by Bao‐Gang Wu, John H. Erdman and J. William Doane. First published in Liquid Crystals, 5, 1453‐1465 (1989).

Progress in flexible and drapable reflective cholesteric displays

— Recent results from encapsulation work on the development of flexible and drapable cholesteric liquid-crystal displays (LCDs) on substrates such as thin plastics, fabrics, and even paper will be presented. The approaches used to create flexible displays using single- and dual-substrate methods based on printable emulsions and polymerization-induced phase-separation (PIPS) techniques will be discussed.

Temperature dependence of the Maier–Saupe order matrix from 2H–NMR of fluorene‐d10 in the nematic, smectic A, B, and C phases

From 2H–NMR of perdeuterated fluorene (diphenylenemethane‐d10) dissolved in 4‐n‐butyloxybenzylidene‐4‐n‐octylaniline (4O.8) and in a mixture of 4O.8 with 4‐4′‐bis‐n‐heptyloxyazoxybenzene (HOAB, 15.1 wt. %) we have measured each of the orientational order parameters of the Maier–Saupe order matrix and their temperature dependence in the nematic, smectic A, smectic B, and smectic C phases, respectively. The fluorene‐d10 molecule, being a rigid structure of known conformation and one which contains a sufficient number of differently oriented deuterated sites, allows for the complete determination of the order matrix in terms of the measured 2H–NMR spectral splittings. The results show: (1) The principal molecular z axis (most ordered axis) is parallel to a direction which joins the centers of the six membered rings at all temperatures and in each phase studied; (2) nonlinearities are present in the temperature dependence of the ratios of the splittings and are a result of the temperature dependence of the el...