Janus Microdroplets with Tunable Self‐Recoverable and Switchable Reflective Structural Colors

Abstract

Microdroplets made from chiral liquid crystals (CLCs) can display reflective structural colors. However, the small area of reflection and their isotropic shape limit their performance. Here, Janus microdroplets are synthesized through phase separation between CLCs and silicone oil. The as‐synthesized Janus microdroplets show primary structural colors with ≈14 times larger area compared to their spherical counterparts at a specific orientation; the orientation and thus the colored/transparent states can be switched by applying a magnetic field. The color of the Janus microdroplets can be tuned ranging from red to violet by varying the concentration of the chiral dopant in the CLC phase. Due to the density difference between the two phases, the Janus microdroplets prefer to orientate the silicone oil side up vertically, enabling the self‐recoverable structural color after distortion. The Janus microdroplets can be dispersed in aqueous media to track the configuration and speed of magnetic objects. They can also be patterned as multiplexed labels for data encryption. The magnetic field‐responsive Janus CLC microdroplets presented here offer new insights to generate and switch reflective colors with high color saturation. It also paves the way for broader applications of CLCs, including anti‐counterfeiting, data encryption, display, and untethered speed sensors.

Janus Dual Self‐Strengthening Structure of Bi2O3/Gd2O3 Nanofibrous Membranes for Superior X‐Ray Shielding

“…[45,46] To confirm this conjecture, we simulated the velocity distribution in FJNMs and Bi 2 O 3 /Gd 2 O 3 flat film (Figure 4c). [47][48][49] The airflow field, which used color as a scale, showed that the exhibited colors of Bi 2 O 3 /Gd 2 O 3 flat film, which ranged from cyan to red, were noticeably different from the colors of blue for FJNMs, emphasizing the role of fibrous porous in boosting air permeability. The FJNMs have a promising heat diffusion pathway thanks to the high WVTR and air permeability.…”

Complex-Shape Solid-State Photonic Droplets Prepared via Phase Separation and Microfluidics

“…The same group reported a highly responsive optical biosensor with phase-separated CLC/FCO droplets . Liu et al fabricated Janus microdroplets through phase separation of CLC and silicone oil with an oligomer mixture . The as-synthesized Janus microdroplets showed primary structural colors with ∼14 times larger area compared with their spherical counterparts at a specific orientation.…”

“…9 Liu et al fabricated Janus microdroplets through phase separation of CLC and silicone oil with an oligomer mixture. 10 The as-synthesized Janus microdroplets showed primary structural colors with ∼14 times larger area compared with their spherical counter-parts at a specific orientation. The curved surface leads to the coupling of the lensing effect of the silicone oil and Bragg's reflection of the CLC part.…”

Iridescence from Total Internal Reflection at 3D Microscale Interfaces: Mechanistic Insights and Spectral Analysis

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These structures have geometric periodicities on the scale of visible light wavelengths, typically hundreds of nanometers, to generate optical path differences (OPDs) between light rays that produce interference coloration. [10,11] Efforts to explore materials that combine multiple optical phenomena across length scales, such as pairing liquid crystals with Janus droplet reflectors [12] or microscale wrinkling of photonic crystal paper, [13] have been shown to lead to unique, tunable structural color effects. Recently, we reported a new optical mechanism for creating structural coloration, wherein interference occurs between light rays undergoing multiple bounces of total internal reflection (TIR) within larger, microscale concave geometries such as hemispheres.

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