Design of Interactive Meta-holographic Display using Liquid Crystallinity

Liquid crystals have been widely used to design reconfigurable materials that sense external stimuli and modulate properties of light. Here, we propose general and versatile approach to enable active metahologram by integrating the thin layer of stimuli-responsive LC layer into multiplexing-metasurfaces. We demonstrate the new class of metahologram can dynamically change homographic images in response to a programmed stimulus (e.g. electric field, heat, pressure and toxic gas).1

Design of Interactive Meta-Holoraphic Display using Liquid Crystallinity

Liquid crystals have been widely used to design reconfigurable materials that sense external stimuli and modulate properties of light. Here, we propose general and versatile approach to enable active metahologram by integrating the thin layer of stimuli-responsive LC layer into multiplexing-metasurfaces. We demonstrate the new class of metahologram can dynamically change homographic images in response to a programmed stimulus (e.g. electric field, heat, pressure and toxic gas).2

Design of Liquid Crystalline Sensor for Carbon Nanotube Agglomerations

Carbon nanotube (CNT)-based transistor has been considered as a promising substitute for silicon-based transistor due to low power consumption and propagation delay time.[1] In the preparation of CNT thin film, it has been shown that CNTs naturally bundle together forming agglomerations. Because the CNT agglomerations play as defect sites impeding electron flow,[2] the detection of CNT agglomerations is required for the design of CNT-based devices. Due to their nanoscale size, however, they were detected by Scanning Electron Microscope (SEM) that is time consuming and can only be applied to nano-to-micro scale area. In this work, we propose a facile and generalized method to instantaneously detect the surface defects in large area by leveraging anisotropic properties (elasticity and birefringence) and long range molecular ordering of liquid crystals (LCs). We prepared LC injected non-agglomeration and agglomeration-rich samples and compared them by POM image. (Fig 1) While the non-agglomeration sample shows a black texture, the agglomeration-rich sample shows a distinct bright dot texture in POM image. The dark texture is caused by vertical ordering of LCs. The bright texture is caused by tilted long range ordering of LCs against the substrate magnifying the nanoscale defect to the visible scale texture. The proposed method enables fast and whole-area detection of CNT agglomerations possible. Furthermore, this method can be used to detect general surface defect.1

Design of Interactive Metahologram via Liquid Crystallinity

The arrays of subwavelength-scaled nanostructures on a surface, often called metasurfaces, have made advances in flat optics because of their potential to display programmable hologram and miniaturize optical components. Because previous metasurface systems are passive, however, their practical applications have been impeded. Accordingly, recent efforts have focused on the realization of active metasurfaces that can switch holograms upon triggers via using, for example, phase-change materials, mechanical actuations, and chemical reactions. Nevertheless, the full potential of active metasurface system has yet to be realized due to the limitation of previous approaches, including limited design of nanostructures, complex fabrication process, and slow response. Here, we propose a simple and versatile design rule to enable dynamically tunable metahologram systems by leveraging the optical anisotropic and stimuli-responsive nature of liquid crystals (LCs). We demonstrate the new class of active metahologram, a thin layer of LC integrated with multiplexing metasurface, to autonomously sense a programmed stimulus (e.g., electric field, temperature, pressure, toxic gas) and dynamically switch the holographic images [1,2,3]. These attribute provides insight into the rational design of interactive meta-hologram display that enable their full potential of multifunctional active devices. This work was supported by the Korea National Research Foundation (NRF-2021R1A4A1030944 & 2021R1A2C2095010).1

Design of Organic Ionic Plastic Crystal based Liquid Crystal Gas Sensor with Tailored Selectivity and Sensitivity

Due to extraordinary sensitivity on a variety of stimuli, Liquid Crystal (LCs) have been widely used for the design of gas sensor. Especially, anisotropy-driven amplification properties of LCs enable high sensitivity, fast response, and low cost. However, selectivity issues have been pointed out. To overcome this limit, we report a new type of highly selective LC gas sensor with wide designing rule using imidazole based organic ionic plastic crystal(OIPC). Specifically, imidazolium groups in an OIPC layer selectively adsorb gas molecules with carboxylic group (e.g., acetic acid) and change the molecular ordering of overlying LCs, leading to macroscopic optical output. In addition, we found sensitivity of the sensor can be precisely modulated by controlling carbon chain length and type of counter ion in OIPC. Overall, our results provide insight into the rational design of gas sensors with high selectivity and sensitivity.2

Design of Holographic Chemical Sensor via Liquid Crystals dope with Chemical Selector

e recently designed new class of interactive meta-holographic display with a combination of polarization multiplexing metasurface and stimuli-responsiveness of liquid crystals (LCs). By leveraging our recent works, here we propose the holographic chemical sensor that autonomously senses a target chemical and reports it via direct holographic alarm. Additionally, by doping a chemical selector into LCs, we demonstrate our system to be able to not only precisely control selectivity but also sensitivity toward programmed chemical.1

Design of Interactive Meta-Holographic Display Using Liquid Crystallinity

The arrays of subwavelength-scaled nanostructures on a surface, often called metasurfaces, have made advances in flat optics because of their potential to display programmable hologram and miniaturize optical components. As previous metasurface systems are passive, however, their practical applications have been impeded. Accordingly, recent efforts have focused on the realization of active metasurfaces that can autonomously switch homographic images upon arrival of triggers. Nevertheless, the full potential of active metasurface system has yet to be realized due to the limitation of previous approaches, including limited design of nanostructures, complex fabrication process, and slow response. Here, we propose a simple and versatile approach to enable dynamically tunable metahologram systems by leveraging the optical anisotropic and stimuli-responsive nature of liquid crystals (LCs). We demonstrate the new class of active metahologram, a thin-layer of LCs integrated with multiplexing2

Design of Selective Chemical/Biological Reactions in Liquid Crystals via Chemical Selectors

Due to the unique combination of fluidity of liquids and long-range molecular ordering of crystals, liquid crystals (LCs) have been widely used for design of functional materials that sense a variety of stimuli and report them into macroscopic optical output. Notably, their amplification ability facilitates the extraordinary sensitivity even to nanoscopic and molecular phenomena (e.g., molecular assembly). However, the relatively low selectivity has prevented the realization of their full potential. In this presentation, we will show simple and versatile design rules to control not only selectivity but also sensitivity by decorating the interface of LC films with organic ionics (OIs). Specifically, the resulting OI-LC film was shown to selectively sense and optically report the exposure of specific toxic gas or bacteria even at very low concentration. In addition, we experimentally and theoretically demonstrated that their characteristics are precisely controllable by modulating the length of carbon chain and type of counter ion in OIs. We will also discuss the interactive holographic system via OI-LC film that can provide visual information about their environment, such as the arrival of chemical and biological cues. This work was supported by the NRF (2021R1A4A1030944 & 2021R1A2C2095010 & 2022M3C1A3081312) and Samsung Electronics Co., Ltd.1

Design of holographic gas sensor using liquid crystallinity

The quick and precise detection of hazardous compounds is important in a variety of fields. If the visual reporting is integrated with the detection, there could be a profound impact on practical applications. In this work, we present a new class of compact sensor platform by combining a stimuli-responsive liquid crystals (LCs) and holographic metasurface (MS) as shown in Figure 1 [1]. Specifically, the metasurface composed of nano structures with sub-wavelength scale was programmed to display two holographic images (smile face for safety signal and exclamation mark for alarm signal) upon the transmission of left- (LCP) and right-circularly polarized light (RCP), respectively. The metasurface was integrated with the LC layer that was designed to transform LCP to RCP in the presence of a target gas by leveraging stimuli-responsiveness and optically anisotropic nature of LCs. Consequently, we demonstrated that the LC-MS system to autonomously sense a target gas (e.g, IPA, methanol, chloroform) and instantaneous report it via the holographic alarm. For instance, the proposed LC-MS gas sensor could detect the ultra-low concentration of IPA gas from a marker pen. Moreover, for their wide applicability, we demonstrate the LC-MS sensors to be selectively responsive to various stimulus (e.g. electrical field, heat, pressure) and to be attachable to flat, curved, and flexible surfaces (e.g., safety goggles) via a one-step nanocasting process [1, 2].1

Design of Liquid Crystals Based Rapid Detection for Food Poisoning Bacteria

Sensitive and selective detection of salmonella that causes food-borne diseases is necessary for food safety and prevention of pathogenic infection. Previous methods like polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) require laborious process and long assay time, hence, reduction in detection time is still controversial issues.1 Here we design liquid crystals (LCs) with organic ionics (OIs) system which can realize simple and rapid bacteria detection. Specifically, OIs are self-assembled at the aqueous-LC interface and cause vertical LC ordering, so that light cannot pass through the film; it appears dark. With injection of tryptone which is one of the components of cell culture media, however, LC is gradually reoriented, which leads to formation of domains. Salmonella population rather than motility facilitates LC reorientation and bright texture is observed as light can pass through the film, which enables rapid and sensitive detection. In addition, functionalized or head group modified OIs are expected to improve selectivity of detection as well as sensitivity depending on length of OIs carbon tail in further studies. The exploration of interaction between OIs, tryptone and bacteria can lead to effective biosensor for detection.2