Application Opportunities from Anti-Counterfeiting to Disease Testing Enabled by the Unique Optics of Cholesteric Spherical Reflectors
Alte Bibliothek, 1st floor
Prof. Dr. Jan P. F. Lagerwall
University of Luxembourg
Cholesteric liquid crystals (CLCs) formed by chemically reactive molecules combine three key properties in an extraordinarily attractive and useful way: Their liquid nature allows easy flow-based processing and molding into any shape; their self-organized long-range order modulated into a helical structure with pitch p that can be easily adjusted via the chemical composition yields a periodic modulation of the refractive index and breaks mirror symmetry, turning CLCs into continuously tunable photonic crystals selective in both wavelength and circular polarization; and their single or dual acrylate groups allow us to easily transform the precursor CLC into a solid or elastomeric polymer that retains both shape and internal order. This unique feature set renders reactive CLCs an immensely powerful tool for making advanced functional materials with endless application opportunities.
In this talk I will share the latest results from three of our applied research tracks that focus on making CLC-templated solid spheres, which we call Cholesteric Spherical Reflectors (CSRs), and utilizing their extraordinary optics for solving important problems from very different fields.
- By depositing a drop of transparent curable binder containing a mix of different CSRs onto a surface and then curing the binder into a solid film, we endow any object of interest with a unique unclonable fingerprint that can be used for proof of authenticity and for track–and–trace of products throughout complex supply chains [1-2].
- By functionalizing CSRs with antibody-terminated ligands and confining them in simple test cells we are developing a frugal Rapid Antigen Test that we hope will have greatly reduced antigen threshold concentration for detection, while also allowing for screening for multiple diseases simultaneously, by taking advantage of the circularly polarized colored reflections from CSRs.
- By tuning p into ranges where the reflections are outside the visible spectrum (IR or UV ranges) and depositing the CSRs into fiducial marker patterns (similar to QR-codes) we aim to create a non-invasive infrastructure that give robots and Augmented Reality (AR) devices a greatly improved localization and identification of objects in their surroundings with no visible impact for human occupants, thus supporting the safe coexistence of robots and humans [3–4].
 M. Schwartz et al. Cholesteric Liquid Crystal Shells as Enabling Material for Information-Rich Design and Architecture, Adv. Mater. 30, p. 1707382 (2018).
 Y. Geng et al., Encoding Hidden Information onto Surfaces Using Polymerized Cholesteric Spherical Reflectors, Adv. Funct. Mater. 31, 2100399 (2021).
 M. Schwartz et al. Linking Physical Objects to Their Digital Twins via Fiducial Markers Designed for Invisibility to Humans, Multifunct. Mater. 4, 022002 (2021).
 H. Agha et al. Unclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors. Light, Sci. Appl., 11, 309 (2022).
Jan Lagerwall (M.Sc. Physics 1997; Ph.D. Materials Science, 2002) is professor in physics at the University of Luxembourg since 2014, following previous group leader positions at Martin Luther University Halle-Wittenberg (Germany) and Seoul National University (Korea). His research focuses on soft matter physics, chemistry and materials science, connecting liquid crystals with many other fields, from fiber spinning and microfluidics to art, architecture, robotics and security. The motivation ranges from the scientific beauty to the diverse application opportunities arising through cross fertilization with other disciplines, transcending fundamental and applied research. Jan was awarded one ERC CoG and two ERC PoC grants, the latter being examples of how he actively works to bring the fruits of his group’s academic research to use for society and industry, engaging in a multitude of collaborations and the foundation of spin-off companies.