Photonic Multishells Composed of Cholesteric Liquid Crystals Designed by Controlled Phase Separation in Emulsion Drops

Abstract

Cholesteric liquid crystals (CLCs), also known as chiral nematic LCs, show a photonic stopband, which is promising for various optical applications. In particular, CLCs confined in microcompartments are useful for sensing, lasing, and optical barcoding at the microscale. The integration of distinct CLCs into single microstructures can provide advanced functionality. In this work, CLC multishells with multiple stopbands are created by liquid–liquid phase separation (LLPS) in a simple yet highly controlled manner. A homogeneous ternary mixture of LC, hydrophilic liquid, and co‐solvent is microfluidically emulsified to form uniform oil‐in‐water drops, which undergo LLPS to form onion‐like drops composed of alternating CLC‐rich and CLC‐depleted layers. The multiplicity is controlled from one to five by adjusting the initial composition of the ternary mixture, which dictates the number of consecutive steps of LLPS. Interestingly, the concentration of the chiral dopant becomes reduced from the outermost to the innermost CLC drop due to uneven partitioning during LLPS, which results in multiple stopbands. Therefore, the photonic multishells show multiple structural colors. In addition, dye‐doped multishells provide band‐edge lasing at two different wavelengths. This new class of photonic multishells will provide new opportunities for advanced optical applications.

Encoding Hidden Information onto Surfaces Using Polymerized Cholesteric Spherical Reflectors

“…To minimize scattering and specular reflection at the binder-CSR interfaces, we must at the same time ensure ≈ b n n, where n is the average refractive index of the CSRs. The analysis also shows that CSR shells are highly superior to droplets for applications in markers, hence the recently demonstrated method of making CLC shells using phase separation in droplets, [19] which can easily be scaled up to large-volume production of CSRs, may become very useful, as it is fully compatible with the new procedures presented in this paper. An excellent first target where CSR-based fiducial markers could be introduced is construction, which at present is in the process of being increasingly automized using robots, hence the markers could be included in building components as the environment is being constructed.…”

“…The elucidation of the peculiar near-field optical properties of CSRs [16] and subsequent recognition that these properties turn CSR arrays into physical unclonable functions (PUFs), [17] of great value in anti-counterfeiting, [18] triggered a surge of follow-up research, [11,16,17,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] identifying many further application opportunities. In the present paper we instead target applications of the far-field selective retroreflection of CSRs, focusing on the ability to encode information unobtrusively onto surfaces.…”

Linking physical objects to their digital twins via fiducial markers designed for invisibility to humans

“…CSRs are made by bringing cholesteric liquid crystals (CLCs) into spherical shape, in form of a droplet [22][23][24][25][26][27] or a shell [18,26,[28][29][30][31][32][33]. The latter is a droplet of CLC which itself contains a droplet of immiscible isotropic liquid.…”

“…In fact, from the point of view of the PUF security quality of CSR fiducials, dispersity is even highly beneficial. Since it is easy to make CSR droplets with high dispersity in simple stirring procedures [22] that can be scaled up, and as it was recently demonstrated that CSR shells can also be made from droplets by the use of controlled phase separation [33], upscaling of CSR production for the use in fiducial markers can thus today be considered a practical problem that is straightforward to solve. To use the CSRs they must finally be turned into a solid, achieved by using reactive molecules such as acrylate or epoxide LC-formers and chiral dopants.…”

Microfluidic generation of barcodes with in situ synthesized perovskite quantum dot encapsulation

“…Herein, we presented a novel strategy for the in situ fabrication of PQD-encapsulated barcode particles for multiplex bioassays with the assistance of microfluidic technique, as schemed in Figure 1. Microfluidics has been widely used to generate monodisperse droplet templates because of their advantages in controllability and stability [14][15][16][17][18][19][20][21][22]. Com-pared with the traditional methods, microfluidic technique is more accurate and flexible by adjusting the fluid volume ratio of raw materials in the preparation process, which has great potential in the synthesis of particles with different morphologies and functions [23][24][25].…”