Constructing and tuning self‐organized three‐dimensional (3D) superstructures with tailored functionality is crucial in the nanofabrication of smart molecular devices. Herein we fabricate a ...self‐organized, phototunable 3D photonic superstructure from monodisperse droplets of one‐dimensional cholesteric liquid crystal (CLC) containing a photosensitive chiral molecular switch with high helical twisting power. The droplets are obtained by a glass capillary microfluidic technique by dispersing into PVA solution that facilitates planar anchoring of the liquid‐crystal molecules at the droplet surface, as confirmed by the observation of normal incidence selective circular polarized reflection in all directions from the core of individual droplet. Photoirradiation of the droplets furnishes dynamic reflection colors without thermal relaxation, whose wavelength can be tuned reversibly by variation of the irradiation time. The results provided clear evidence on the phototunable reflection in all directions.
Blue rays: Photoirradiation of self‐organized, phototunable 3D photonic superstructures of monodisperse droplets of a cholesteric liquid crystal (CLC) containing a photosensitive chiral molecular switch gives dynamic reflection colors. The colors can be tuned reversibly upon light irradiation, and in groups of droplets blue‐ray patterns arise from photonic cross‐communication between neighboring droplets.
Liquid crystal droplets have shown unique response performance due to their exclusive optical properties and dispersion. However, the stability of LC droplets during storage and application needs to ...be improved. Here, we report a novel LC droplet sensing platform to improve the stability of LC droplets significantly. By embedding LC droplets into polyacrylamide hydrogel films, the LC droplets can be preserved for four months without noticeable volume loss and any aggregation even in the absence of surfactant. Interestingly, LC droplets exhibit remarkable stability even in ethanol and N,N-Dimethylformamide aqueous solution. Besides, the mechanical properties of hydrogel film do not reduce after embedding LC droplets. Specifically, the introduction of LC droplets improves the elasticity of the hydrogel film. As a sensing platform, the response performance of the LC droplet-embedded hydrogel film is investigated. After being exposed to ATP solution as low as 1 ng/mL, LC droplets can generate optical signal changes which can be observed by the naked eye. The strategy presented here provides a new sight for the design of LC droplet sensors and contributes to the practical application of LC droplet sensors.
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•A model to describe the electro-optical response of PDLCCNT films is developed.•Experimental verification of the model is performed.•The model is applied for the films with uniform normal interface ...anchoring.•A technique connecting the mass and volume filling factors of the films is created.
An optical model has been developed for analyzing the coherent transmittance of a polymer dispersed liquid crystal films doped with carbon nanotubes (CNTs) at uniform normal droplet-polymer interface anchoring. It is based on the Foldy–Twersky and anomalous diffraction approximations, Maxwell-Garnett equations, and the order parameters concept. The model allows one to analyze the electro-optical response of films depending on their thickness, the refractive indices of the liquid crystal (LC) and polymer matrix, size and concentration of the LC droplets, concentration of nanotubes, conductivities of the LC and the polymer. Experimental verification of the model is performed.
An important goal of the modern soft matter science is to discover new self-assembly modalities to precisely control the placement of small particles in space. Spatial inhomogeneity of liquid ...crystals offers the capability to organize colloids in certain regions such as the cores of the topological defects. Here we report two self-assembly modes of nanoparticles in linear defects-disclinations in a lyotropic colloidal cholesteric liquid crystal: a continuous helicoidal thread and a periodic array of discrete beads. The beads form one-dimensional arrays with a periodicity that matches half a pitch of the cholesteric phase. The periodic assembly is governed by the anisotropic surface tension and elasticity at the interface of beads with the liquid crystal. This mode of self-assembly of nanoparticles in disclinations expands our ability to use topological defects in liquid crystals as templates for the organization of nanocolloids.
•Optoelectronic tweezers (OET) by using the light-induced dielectrophoresis (DEP) have been applied to control the LC droplets.•The LC droplets experience negative DEP forces in the range of applied ...frequencies, 20 – 100 kHz.•A velocity of 180 μm/s can be achieved for a 30-μm-diameter LC droplet by applying 6.5 V at 20 kHz.•Patterning LC droplets are demonstrated.
Optoelectronic tweezers (OETs) by using the light-induced dielectrophoresis (DEP) have been applied to control the isotropic objects with sizes from nanometers to micrometers. The ability to control anisotropy and birefringent materials like liquid crystals (LC) by OETs is promising for finding more photonic applications. Unlike conventionally manipulated isotropic objects, the LC directors inside the LC droplet are influenced by the external electric field during OETs operation. We have demonstrated that LC droplets in an aqueous solution can be dynamically manipulated and patterned by OETs even though the LC directors inside the droplet are changed with the external electric field. The propulsion speeds of the LC droplets in terms of droplet size, light pattern linewidth, strength and frequency of the applied electric field are characterized by applying a rectangular light pattern. A velocity of 180 μm/s is achieved for a 30-μm-diameter LC droplet by applying 6.5 V at 20 kHz.
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•The micrometer-sized 5CB droplets coated with an amphiphilic block copolymer of PAA-b-LCP were utilized for glucose detection.•The receptor APBA was coupled to the PAA chains via ...EDC×NHS coupling between the acrylic groups of PAA and the amine groups of APBA.•The binding events between APBA and glucose were translated by configurational change (from radial to bipolar) of the 5CB droplets.•LC droplet-based non-enzymatic biosensor for glucose detection exhibited high sensitivity, selectivity, and good stability for 30 days.
3-Aminophenyl boronic acid (APBA)-decorated 4-cyano-4′-pentylbiphenyl (5CB) microdroplets were utilized for glucose detection with high specificity and sensitivity. APBA decoration was performed by firstly coating poly(acrylic acid) (PAA) on the 5CB droplet with amphiphilic poly(4-cyanobiphenyl-4′-undecylacrylate-b-acrylicacid) (LCP-b-PAA) and performing covalent bonding of APBA to the PAA chains by EDC coupling between the acrylic groups of PAA and the amine groups of APBA. The binding events between APBA and glucose were translated by configurational change (from radial to bipolar) of the 5CB droplets, observed under a polarized optical microscope with crossed polarizers. The liquid crystal (LC) droplet-based non-enzymatic (NE) biosensor for glucose detection exhibited high sensitivity (detection limit of 0.05mM) even in complex serum sample, high selectivity against cholesterol, uric acid, and acetaminophen, and good stability for 30 d. This NE-based glucose LC biosensor is cost-effective and highly stable compared to enzyme-based LC glucose biosensors and thus, could replace such enzyme-based biosensors.
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We report the surface modification of 4-n-pentyl-4’-cyanobiphenyl (5CB) droplets in aqueous solution by the adsorption of sulfated β-CD/tetradecyl sulfate sodium (SC14S) complexes at ...the 5CB-aqueous interface, followed by the coating of poly(diallyldimethylammonium chloride) (PDADMAC) through electrostatic interaction. The PDADMAC/sulfate β-CD/SC14S complex-coated 5CB droplets are highly stable in aqueous solution. We show that bile acids are able to penetrate into the PDADMAC coating and displace the SC14S from the cavity of the β-CD immobilized at the surface of the 5CB droplets through the competitive host-guest recognition, consequently inducing the radial-to-bipolar configuration transition of the 5CB droplets. The integration of PDADMAC/sulfate β-CD/SC14S complex-coated 5CB droplets in microfluidic channels allows the selective detection of bile acids in a small sample volume (1 μL) in the presence of ascorbic acid, uric acid, creatinine and urea by observing the configuration transition of the 5CB droplets. The detection limit of the miniaturized 5CB droplet-based sensor platform for bile acids can be tuned by the number density of 5CB droplets.
Self-propelled droplets made of organic materials can be an influential candidate for understanding cell migration from the viewpoint of nonequilibrium physics and have attracted significant ...attention with regard to soft-matter-type rovers. Because self-propelled droplets are soft enough to be easily deformed, they should be useful as chemically artificial rovers that can move in small areas with many obstacles in water and can be applied as ‘motile’ carriers for exploring and curing of biological bodies or remediation of the natural environment. Here, we review recent research progress on designing self-propelled droplets of micrometer size.
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Liquid crystals represent a fascinating intermediate state of matter, with dynamic yet organized molecular features and untapped opportunities in sensing. Several works report the use of liquid ...crystal droplets formed by microfluidics and stabilized by surfactants such as sodium dodecyl sulfate (SDS). In this work, we explore, for the first time, the potential of surface-active ionic liquids of the imidazolium family as surfactants to generate in high yield, stable and oriented liquid crystal droplets. Our results show that C12MIMCl, in particular, yields stable, uniform and monodisperse droplets (diameter 74 ± 6 µm; PDI = 8%) with the liquid crystal in a radial configuration, even when compared with the standard SDS surfactant. These findings reveal an additional application for ionic liquids in the field of soft matter.
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•Polymer hydrogel dispersed liquid crystal droplet sheets are fabricated.•The real-time detection of ionic surfactants and bile acids is achieved with hydrogel dispersed liquid ...crystal droplets as an optical probe.•The sensor properties of hydrogel dispersed 5CB droplet sheets can be tuned by properly changing the charge of polymer networks.•The response time and range for ionic surfactants and bile acids depend on their electrostatic interaction with charged polymer networks.
Polymer hydrogel dispersed liquid crystal (LC) droplets are a promising LC based sensor platform. However, the influence of polymer networks on the sensor performance of hydrogel dispersed LC droplets has not been fully understood. Here, neutral and charged polymer hydrogel dispersed LC droplet sheets are designed by the gelation of agarose and chitosan stabilized LC emulsion films formed on glass substrates. Ionic surfactants and bile acids are able to penetrate into the hydrogel sheets and travel to the surface of the dispersed LC droplets, triggering the director configuration transition of the LC inside the droplets. The real-time observation of the configuration transition of the dispersed LC droplets reveals that the polymer networks are able to modulate the penetration and travel of surfactants and bile acids in the hydrogel sheets through electrostatic interaction, consequently tuning the response time and range of the dispersed LC droplets in sensing ionic surfactants and bile acids.
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