pH-responsive cholesteric liquid crystal double emulsion droplets prepared by microfluidics

Jang, Ju-Hyun; Park, Soo‐Young

doi:10.1016/j.snb.2016.10.118

Cited by 73 publications

(45 citation statements)

References 47 publications

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“…The differences between these platforms depend on the orientation of the LCs and the interpretation of the optical signal. Droplet platforms have received much attention due to their large specific surface areas, high sensitivities, and simple preparation methods . The main operating principle of an LC sensor is based on the change in the anchoring direction of the LCs (horizontal to vertical or vertical to horizontal).…”

Section: Introductionmentioning

confidence: 99%

“…Droplet platforms have received much attention due to their large specific surface areas, high sensitivities, and simple preparation methods. [27][28][29][30][31][32] The main operating principle of an LC sensor is based on the change in the anchoring direction of the LCs (horizontal to vertical or vertical to horizontal). Pretreatment allows droplets to respond to various environmental changes, such as pH, enzymatic reactions, etc.…”

Section: Introductionmentioning

confidence: 99%

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Fabrication of Liquid Crystal Droplet Patterns for Monitoring Aldehyde Vapors

Jang

2019

ChemPlusChem

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A sensing method based on the pattern of liquid crystal droplets was developed for detecting and monitoring low levels of organic aldehyde vapors. Exposure of the LC droplet pattern covered with glycine solution to aldehyde vapors induced an optical signal transition from a bright fan shape to a dark cross appearance, as observed by polarized light microscopy. Aldehyde and glycine react at the air/solution interface to form a Schiff‐base compound, which controls the orientation of the LCs and induces a change in the optical signals of the LC droplet pattern. The results show that the glycine/LC droplet pattern system is particularly sensitive and selective to aldehydes. In the actual environment, the sensor is exposed to the aldehyde and the signal transition is completed within a few minutes (2–7 min). The LC‐based method has the advantages of simple construction, easy operation, convenient data reading, and shows excellent prospects for real‐time detection of aldehyde vapors.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Fabrication of Liquid Crystal Droplet Patterns for Monitoring Aldehyde Vapors

Jang

2019

ChemPlusChem

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“…Particularly attractive optical phenomena arise when ChLCs are curved into spheres with radially aligned helix, for instance in droplets or shells (thin layer of ChLC surrounding an internal isotropic droplet). Among recently demonstrated or predicted manifestations of the potential of spherical ChLCs are omnidirectional tunable lasers and chiral mirrors, wavelength‐selective photonic couplers/distributors, photonic ink, pH‐, hydrogen peroxide and biosensors, spontaneous nanoparticle segregation, and unclonable patterns for secure authentication generated by arrays of ChLC shells . So far, the optical properties were analyzed under the assumption that all light is reflected at the exterior of the ChLC and—with the exception of one paper suggesting a slightly ellipsoidal deformation—that the droplets are perfect spheres, with full rotational symmetry.…”

Section: Introductionmentioning

confidence: 99%

Through the Spherical Looking‐Glass: Asymmetry Enables Multicolored Internal Reflection in Cholesteric Liquid Crystal Shells

Geng

Jang

Noh

et al. 2017

Advanced Optical Materials

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tunable lasers [5] and chiral mirrors, [6] wavelength-selective photonic couplers/distributors, [7,8] photonic ink, [9] pH-, hydrogen peroxide and biosensors, [10][11][12] spontaneous nanoparticle segregation, [13] and unclonable patterns for secure authentication generated by arrays of ChLC shells. [14] So far, the optical properties were analyzed under the assumption that all light is reflected at the exterior of the ChLC and-with the exception of one paper suggesting a slightly ellipsoidal deformation [15] -that the droplets are perfect spheres, with full rotational symmetry. Is this assumption justified and does the neglect of possible deviations have consequences on the optical properties?For shells, full rotational symmetry is not necessarily to be expected, since perfect density matching between the inner isotropic liquid and the surrounding ChLC phase is difficult to achieve, and because experiments have shown that at least a nonchiral nematic prefers asymmetric shells, as this allows minimization of the free energy cost related to topological defects. [16] While recent theoretical work [17] suggests that a short-pitch ChLC promotes symmetric shells with a close to central position of the inner droplet, this has until now not been experimentally corroborated. In this paper we show that ChLC shells can change over time from nearly symmetric to strongly asymmetric, via a close competition between symmetry-restoring elasticity of the cholesteric helix and symmetry disrupting buoyancy. We demonstrate that this variation in shell geometry has dramatic implications for the photonic behavior.Symmetric shells and asymmetric shells with thick top (promoted by an inner phase denser than the ChLC) illuminated by white light Spheres of cholesteric liquid crystal generate dynamic patterns due to selective reflection from a helical structure subject to continuously curved boundaries. So far the patterns are investigated exclusively as function of reflections at the sphere exterior. Here it is shown that the cholesteric shells in a microfluidics produced double emulsion enable also a sequence of internal reflections if the shells have sufficiently thin top and thick bottom. While such asymmetry is promoted by buoyancy when the internal droplet has lower density than the liquid crystal, the elasticity of the cholesteric helix prefers a symmetric shell geometry, acting against gravity. This subtle balance can hide the internal reflections for long time. Eventually, however, the asymmetry is established, revealing a new class of photo nic patterns characterized by colored sharp concentric rings. With the complete knowledge of the diverse light-reflecting behavior of cholesteric liquid crystal shells, and utilizing the tunability of the structure period by, e.g., temperature, electric field, or exposure to various chemical species as well as polymer stabilization for making the shells long-term stable, they may be developed into remarkable new optical elements for photonics, sensing, or security pattern generation.

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“…In this case the ordered long alkyl chains of surfactant molecules orient the LC molecules [7,10,11]. The parameters of orienting layer and, consequently, the surface anchoring can be varied by changing the concentration of surfactant dissolved in LC [12] or in the ambient solution [13], pH of the ambient medium [14,15], temperature [16] or upon UV irradiation [17,18]. Using of ionic surfactants allows modifying the orienting influence of definite interface area due to the applied voltage which changes the ion concentration at the corresponding part of droplets [19][20][21][22] or on the substrate of flat LC cells [23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Anionic-cationic surfactant mixture providing the electrically controlled homeotropic surface anchoring of liquid crystals

Krakhalev

Sutormin

Prishchepa

et al. 2019

Journal of Molecular Liquids

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4-heptyloxybenzoate benzyl dodecyldimethylammonium (HOBBDDA) is synthesized and its orienting influence on nematic liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) is tested. HOBBDDA dissolved up to 1.4 percent in 5CB droplets dispersed in polymer film does not change the tangential surface anchoring inherent to polyvinyl alcohol matrix used. Homeotropic surface anchoring is realized if the HOBBDDA content exceeds 1.7 percent. The molecules of the surfactant in 5CB dissociate into anions and cations. The anions modify the surface anchoring under the action of DC electric field both in the normal and inverse mode. The mixture of HOBBDDA and cetyltrimethylammonium bromide can function as a binary ioniccationic surfactant which significantly expands the prospects for using the ionic-surfactant method to control liquid crystal materials.

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pH-responsive cholesteric liquid crystal double emulsion droplets prepared by microfluidics

Cited by 73 publications

References 47 publications

Fabrication of Liquid Crystal Droplet Patterns for Monitoring Aldehyde Vapors

Fabrication of Liquid Crystal Droplet Patterns for Monitoring Aldehyde Vapors

Through the Spherical Looking‐Glass: Asymmetry Enables Multicolored Internal Reflection in Cholesteric Liquid Crystal Shells

Anionic-cationic surfactant mixture providing the electrically controlled homeotropic surface anchoring of liquid crystals

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