9 research outputs found
Self-Regulating Surface Encapsulation of Liquid Crystals
No full textLiquid crystals (LCs) are complex fluids with both crystal-like long-range molecular ordering and liquid-like fluidity, leading to anisotropic properties (e.g., birefringence and elasticity) [1, 2]. This combination of properties provides the ability to change molecular orientations and thus report corresponding optical signals in response to a variety of physical and chemical cues, including surface modifications, pressure, and electric fields.
In this work, we report a simple and versatile approach to produce LC droplets encapsulated by polymeric amphiphiles on substrates with controllable size and density upon thermal trigger. As shown in Fig. 1(a), the simplest system to observe the new approach is to place LCs between two glass substrates coated with poly (octadecyl methacrylate) (PODMA). At a room temperature (T0 = 25oC), the cells show a dark texture between crossed-polarizers (Fig. 1a) indicating a vertical orientation of LCs at substrates induced by the long aliphatic tails of PODMA. When the substrates were heated above 30oC and cooled back to T0, however, we observe the appearance of birefringent domains at substrates corresponding to radial configuration of LCs within the domains (Fig. 1b). The results suggest PODMA can play a role in thermally triggerable local encapsulation of LCs (and thus local reorientation of LCs). Specifically, with a use of polarizing optical and confocal fluorescence microscopy, we demonstrate the underlying mechanism of the thermo-optical effects to be related to thermal-induced diffusion of PODMA into LCs and their micelle formation. We found the size and density of locally encapsulated LC droplets to be controllable via heating temperature, rate of temperature changes, type of LCs, and length of aliphatic tails in PODMA, which also support our underlying mechanism.
We envisage that the new thermo-optical phenomena will find applications in a variety of field, including sensors, photonics, surface modification, and structure patterning. In addition, it will be of interest to use the described mechanism to design the system that are triggered by various triggers beyond temperature.1
Design of Liquid Crystal Elastomer Droplets with Versatile Actuation Properties
No full textIn nature, twisting motions of many organisms enable complex mechanical function such as swimming, crawling, climbing and energy storage. Liquid crystal elastomers (LCEs) are anisotropic polymeric materials which are promising candidates for the soft-actuator owing to their capability of stimuli-responsive properties. In this work, we report the highly reversible three-dimensional torsional actuation of LCE droplet using heat. LCE droplet was obtained by removing non-polymerizable mesogen after simply mixing non-polymerizable and polymerizable mesogen. We verify the twisted configuration and twisting mechanism of LCE with fluorescence confocal polarizing microscopy. In addition, we designed asymmetric LCE droplet by phase separation of LCE and by simply tuning droplet configuration. This versatile twisting actuation of LCE droplet give us fundamental of shape control of LCE and design self-swimming particles. This work was supported by the NRF (2021R1A2C2095010, 2022M3C1A3081312).2
Field Surveys for the environmental impact assessment of a potential offshore storage site in the East Sea
No full textTo obtain baseline data for the potential offshore storage site located in the southwestern part of the East Sea,, we have conducted four field surveys during 2012. The base line data we obtained will be used in environmental impact assessment and site characterization. We have conducted one field survey that covered wider area including the potential storage site and three surveys focused on the site. We have measured physical and chemical properties of sea water including temperature, salinity, pH, various nutrients, and CO2 concentration. We also conducted ecological monitoring for planktonic, nectonic and benthic communities. Sediment cores were also taken to assess the benthic environment. To monitor the benthic community better, experiments using a benthic chamber were conducted. To quantify mixing, 24 hours long continuos measurement of was conducted. Results from these fields experiments will be presented using the presentationessment and site characterization. We have conducted one field survey that covered wider area including the potential storage site and three surveys focused on the site. We have measured physical and chemical properties of sea water including temperature, salinity, pH, various nutrients, and CO2 concentration. We also conducted ecological monitoring for planktonic, nectonic and benthic communities. Sediment cores were also taken to assess the benthic environment. To monitor the benthic community better, experiments using a benthic chamber were conducted. To quantify mixing, 24 hours long continuos measurement of was conducted. Results from these fields experiments will be presented using the presentation2
Design of Holographic Chemical Sensor via Liquid Crystals dope with Chemical Selector
No full texte 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
Enhanced Security Platform via Active Multi-band Metasurface with Tunable Heliconical Liquid Crystal Modulators
No full textMetasurfaces that are composed of nanostructures with subwavelength-scale (meta-atoms) have the ability to precisely modulate phase and amplitude of incident electromagnetic waves based on the design of meta-atoms (e.g, organization, shape, size, materials). The encoded information on metasurfaces can be decrypted and be shown as optical signals only upon specific keys such as polarization, amplitude, wavelength, and incidnet angle of light [1]. Due to infinite degrees of freedoms of light, therfore, the metasurfaces have been proposed as a promising high security platform beyond previous security systems with a limited number of encryption. To enhance optical security, previous works demonstrated bifunctional metasurfaces that were fully decrypted by combination of multiple keys (e.g. polarization and wavelength) [2, 3]. Moreover, we reported active metasurface incorporated with liquid crystals (LCs) that can modulate optical keys [3, 4].
Based on this, we propose herein the enhanced security platform via active multi-band metasurface integrated with tunable heliconical LC modulators that can control reflection wavelength (Fig. 1a). The heliconical LCs can reflect specific wavelength via Bragg reflection due to pitch between internal quasi-layers [5]. The wavelegnth can be tuned from ultraviolet to infrared range by electric field (Fig. 1b) that changes the cone angle of LC molecules associated with the pitch. Therefore, metasurfaces with heliconical LC modulators are doubly encrypted by incident and reflection wavelength, which can be only decrypted when the both wavelength match.
This method provides high security platform with active LC modulators. The heliconical LCs can be designed with various stimuli such as temperature and chiral dopants, thus we envisage that the proposed simple method can broaden security and anticounterfeiting platform.1
