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Formation of "chevron" layer structures on cooling a parallel-aligned planar homogenous sample through the nematic-Smectic A to Smectic C* sequence. a) Formation of C1 and C2 layer tilt; b) Smectic layer distribution at 30°C for the commercial FLC mixture SCE13 determined by X-ray diffraction; c) Temperature dependence of the layer spacing, layer tilt and optical cone angle.
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Ferroelectric liquid crystals (FLCs) were a major topic for research in the 1980s and 1990s, to which George Gray and his research family played a fundamental role in developing the field. The famous symbiotic relationship between the chemists at Hull University and device physicists at the Royal Signals and Radar Establishment (RSRE) continued thr...
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Context 1
... this behaviour requires consideration of the smectic layer structure first, and then the director profile of the sample. Figure 3a shows a schematic of the smectic layers in a parallel-aligned sample with a surface pre-tilt θ s of a few degrees. Even with a substantial director pre-tilt causing splay/bend in the aligned nematic phase, the divergence of the bend elastic constant K 33 as the sample cools towards the smectic phase leads to a uniform layer structure. ...
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... with a substantial director pre-tilt causing splay/bend in the aligned nematic phase, the divergence of the bend elastic constant K 33 as the sample cools towards the smectic phase leads to a uniform layer structure. If the pre-tilt on the opposing surfaces is the same, then the S A layers are formed with the layer normal in the plane of the cell and parallel to the rubbing direction r, as shown in figure 3a. As the sample is cooled further into the S C * phase, the layers tilt in opposite directions in the upper and lower halves of the display, forming a symmetric chevron layer structure [6]. ...
Context 3
... T C is the S A to S C (*) transition temperature. The S C layer spacing will also have a similar temperature dependence, as shown in figure 3c. At some temperature in the S A phase, the periodicity of the layers intersecting with the surface is d A . ...
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... d A and d C (T) are the layer periodicities for the S A and S C (*) phases, respectively. Figure 3c shows the temperature dependence of the layer spacing and resultant tilt angle d C for the commercial FLC mixture SCE13 [5,9], together with the S C cone angle θ C . The best fits for this mixture give θ 0 = (52 ± 2)°; ν O = 0.33 ± 0.02; δ 0 = (47 ± 2)°; ...
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Citations
... It is interesting to note that M5 does not follow the loose positive correlation between density increase and transitional enthalpy (supplementary table 2), perhaps due to its composition as a mixture. values of M5. c) A comparison is made of for M5 and 5CB [42] as well as the polar smectics, SCE8 [43] and compounds 1 and 3 from [44,45]. ...
... The observations of M5 and 5CB where an increased density does not result in a larger confirms that Lorentz-Lorenz equation does not adequately explain/ should not be used in the explaining the behaviour of polar liquid crystal materials. To identify any relationship between and spontaneous polarisation M5 is compared with literature data for the polar smectics SCE8 ( 50 ) [43] and compounds 1 and 3 ( 150 ≈ -2 ≈ ) from [44,45] (structures and phase sequences are given in SI section 6). It is possible to use measurements of the density and spontaneous polarisation in a ferroelectric material, together with knowledge of the molecular dipole moment to deduce a value for the polar order parameter . ...
The ferroelectric nematic phase (NF) is a recently discovered phase of matter in which the orientational order of the conventional nematic liquid crystal state is augmented with polar order. Atomistic...
... As an example, the SSFLC device demonstrates ON and OFF times are equally fast and must be latched with an electric pulse due to the inherent bistability of the two states. For the VGA-FLC, the c-director switching time in response to coupling between the spontaneous polarisation P S and applied field E is given by 38,56,57 ...
Ferroelectric liquid crystals remain of interest for display and spatial light modulators because they exhibit significantly faster optical response times than nematics. However, smectic layers are sensitive to shock-induced flow and are usually permanently displaced once a well-aligned sample is disrupted, rendering such devices inoperable. We introduce a vertical alignment geometry combined with a surface-relief grating to control both the smectic layer and director orientations. This mode undergoes “self-healing” of the smectic layers after disruption by shock-induced flow. Sub-millisecond switching between optically distinct states is demonstrated using in-plane electric fields. Self-healing occurs within a second after being disrupted by shock, wherein both the layer and director realign without additional external stimulus. The route to material improvements for optimised devices is discussed, promising faster spatial light modulators for high-speed adaptive optics, micro-displays for virtual/augmented reality and telecommunications with inherent shock stability.
... Ferroelectric liquid crystals (FLCs) were a highly popular research subject for the display industry in the 1980s and 1990s, due to their sub-millisecond switching times and inherent bistability [1]. Technologies such as the Surface Stabilised FLC (SSFLC) [2] seemed suited as an alternative to nematic-based LCDs since high complexity passive displays could be made without thin-filmtransistors at each pixel. ...
... Unwanted helical twist from one surface to the other is ensured by decreasing the chirality of the SmC*, thereby leading to a uniform surface stabilised homeotropic state. Uniform alignment occurs for the condition satisfies P(T) > 4d [1] where P(T) is the helical pitch of the FLC, and d the cell gap, calculated from the Gooch-Tarry equation for a TN device [9]: ...
Sub‐millisecond electro‐optic switching times of ferroelectric liquid crystals (FLCs) remain highly desirable for fast switching devices, such as LCoS display applications. Such materials are notoriously susceptible to damage through shock‐induced flow. A simple shock‐stable geometry for FLC electro‐optic shutters is presented, based on homeotropic surface‐relief gratings.
... As an example, the SSFLC device demonstrates ON and OFF times are equally fast and must be latched with an electric pulse due to the inherent bistability of the two states. For the VGA-FLC, the c-director switching time in response to coupling between the spontaneous polarisation P S and applied field E is given by 38,56,57 ...
Sub-millisecond electro-optic switching times of ferroelectric liquid crystals (FLCs) remain highly desirable for fast switching devices, such as LCoS display applications. Such materials are notoriously susceptible to damage through shock-induced flow. A simple shock-stable geometry for FLC electro-optic shutters is presented, based on homeotropic surface-relief gratings.
... Thus, the polarisation optics can be treated in the same way as a conventional nematic. However, the dielectric biaxiality ¶e = e2-e2 is significant [120,121] and, in essence, acts in a similar fashion to the nematic De, dictating the RMS response of the c-director. ...
... If the field has the correct polarity to reorient the director from one side of the cone to the other, the dielectric biaxiality supresses switching and, above the voltage where the torques balance (≈ 32.5V for these values), the director will remain unswitched indefinitely. In fact, electrical pulses at about 70% of this voltage [121,122] start to slow the response rapidly, creating a minimum in the switching characteristic (tVMIN). Operating close to this voltage (i.e. about 23V, for the high biaxiality SmC* material in this example) gives a highly non-linear response, thereby enabling thousands of lines to be addressed with a high degree of insensitivity to temperature variations and line losses. ...
Over the past half-century, Liquid Crystal Displays have grown to be one of the most successful optoelectronic technologies, becoming an integral part of communication devices and often an enabling technology. This success has required many adaptions to meet the requirements of ever-increasing complexity and performance. Indeed, it is the adaptability of liquid crystal devices that grounds their success. After outlining the basic physics of liquid crystals and device construction, the various modes used in commercial displays will be reviewed, both for mainstream and niche markets, together with a summary of the important complimentary technologies. Finally, liquid crystal devices that have promise for future applications in optoelectronics will be discussed.
... Of course, John's work on smectic liquid crystals was world leading and well known to me too, but I was yet to meet the man, one of the most successful of a distinguished set of coworkers from Gray's group in the nineteen seventies. Over the next decade, I worked very close with John, as described in the edition of Liquid Crystals dedicated to George Gray [3] particularly whilst developing ferroelectric liquid crystals for High-Definition Television (HDTV) operation with Sharp. However, the following account describes work done both alongside that work with John and subsequently. ...
... As the first company to sign an agreement, Sharp won a favourable deal provided that they reinvest some of the royalties directly back into the Displays Group at RSRE. Not only did this secure funding for on-going basic research but also created a relationship with Sharp Japan that was to last the following decade, leading to the HDTV programme on Ferroelectric Liquid Crystals described in [3]. ...
... The 1998 conference was held in Anaheim, California, and the DERA Displays Group took a booth. Alongside sales material relating to DERA's Ferroelectric Liquid Crystal TV technology [3], VCT, [6] and the reconfigurable holographic display based on the Active Tiling of an FLC Optically Addressed Spatial Light Modulator [20], was the 1" diagonal ZBD demonstrator. Each of these innovations garnered interest, but I was particularly struck when demonstrating ZBD to the effervescent Nick Darby from Dow Chemical Ventures, when he volunteered "I'll give you $5M for that technology". ...
The zenithal bistable display (ZBD) was the first liquid crystal device mode to be commercialised that uses nematic disclinations in a constructive fashion, to use the flexoelectric effect inherent to all liquid crystals but at the time was considered too weak an effect to be useful, and to transfer nano-replication methods to the LCD manufacturing environment. The genesis of the invention and spin-out company ZBD Displays Limited will be described, and the evolution of that company from licensing model, through fabless manufacturer to display provider and finally to a system provider for the retail sector. The story may be useful not just to those interested in the science behind a rather unusual LCD, but also those involved in taking technology from laboratory to manufacturing, from idea to commercial success.
... FLCs are promising materials for fast switching electro-optical displays with wide viewing angle [2]; physics behind such devices and optimum material requirements thereof have recently been reviewed by J. C. Jones. [3] FLCs have been the subject of intense investigation not only for their intriguing properties for fundamental condensed matter research, but also for their application in fast switching flat panel displays, optical light modulators, optical signal processing and computing. However, they are not used much commercially because of difficulties at various levels. ...
Three partially fluorinated ferroelectric liquid crystals (4F4R, 4F5R and 7F3R) with biphenylyl benzoate rigid core have been investigated by frequency-dependent dielectric spectroscopy and electro-optic methods. Molecular structures of the compounds differ only by the length of the carbon chain and the number of oligomethylene spacers. 4F4R and 4F5R exhibit ferroelectric SmC* phase over a considerable temperature range and directly melts into isotropic phase, 4F4R also shows a ferroelectric type subphase. Only Goldstone mode (GM) relaxation is observed in these compounds, but no soft mode (SM). 7F3R exhibits both the SmC* and SmA* phases, has higher stability of SmC*. Both the GM and SM relaxations are observed in this case, signifying that SM relaxation is possible only when SmC* is formed on cooling from SmA*. Increase of dielectric strength and critical frequency with temperature, in all cases, has been explained in the light of generalised Landau model. Spontaneous polarisation is found to decrease with increasing flexibility, and optical tilt depends more on fluorination than on chain length.
Tilted smectic liquid crystal phases such as the smectic-C phase seen in calamitic liquid crystals are usually treated using the assumption of biaxial orthorhombic symmetry. However, the smectic-C phase has monoclinic symmetry, thereby allowing disassociation of the principal optic and dielectric axes based on symmetry and invariance principles. This is demonstrated here by comparing optical and dielectric measurements for two materials with highly first order direct transitions from nematic to smectic-C phases. The results show a high difference between the orientations of the principal axes sets, which is interpreted as the existence of two distinct cone angles for optical and dielectric frequencies. Both materials exhibit an increasing degree of monoclinic behavior with decreasing temperature. Due to fast switching speeds, ferroelectric smectic-C* materials are important for fast modulators and LCoS devices, where the dielectric biaxiality influences device operation.
Highly first order silane end-group difluoroterphenyl liquid crystal was added to trifluoroterphenyl host with a nematic to smectic-C phase transition to increase its first order nature, achieve a higher cone angle and reduce its temperature dependence. Increasing concentration of the additive, caused a linear decrease and eventual disappearance of the nematic phase. A smectic-A phase was injected at 35% concentration, making the transition second order. Optical studies of the mixtures showed little dependence of the highest value of cone angle on concentration. The original host showed first order cone angle behavior and was used to fabricate a twisted FLC device.
Spontaneous or induced chiral symmetry breaking in achiral systems is unusual and understanding the origin of such a phenomenon has been an important area of research for several years. The optically isotropic mesophases exhibited by unconventional liquid crystals are one of the most interesting systems to investigate spontaneous chiral symmetry breaking in liquid crystal mesophases formed by achiral moieties. The dark conglomerate (DC) phases are one such optically isotropic family of phases. In this paper, a detailed account of the tendency of bent-core mesogens to form a variety of polar smectic phases, the formation of DC phases due to layers deformations and the general optical, electrical, physical properties of the DC phases are given. An example of a DC phase which exhibit distinct electro-optic properties is described with the nature of dynamics of the response and physical reasons responsible for such behaviour. The challenges and prospects of the DC phases are discussed for their potential applications in novel devices.
