ECLIPSE

ECLIPSE aims to explore totally new methods to realize spherically symmetric particles based on cholesteric liquid crystals, with remarkable reflective optical properties. What makes these Cholesteric Spherical Reflectors (CSRs) exceptional is that they exhibit structural color thanks to a Bragg-reflecting helically periodic internal structure, which also makes the reflected light circularly polarized. When brought into spherical shape, the reflections become omnidirectional while keeping the strong selectivity. We have previously demonstrated that these properties can give CSRs foundational impact by enabling an infrastructure that can assist autonomous navigation, augmented reality, anti-counterfeiting and many other necessary and emerging technologies in our modern societies. However, this attractive long-term perspective is currently hampered by two critical bottlenecks related to CSRs, both of which will be addressed in ECLIPSE.
First, current methods for making CSRs, based on microfluidics, are not amenable to upscaling. In ECLIPSE we will explore two new methods for realizing CSRs that do not have this limitation: electrospray and controlled phase separation guided by confinement in droplets. Apart from having industrial viability, these methods are scientifically fascinating and they are getting significant traction in cutting-edge advanced materials research, yet they have never been combined with the power of liquid crystalline self-assembly as we will do in ECLIPSE. With the research envisaged in the project, we will realize exceptionally small CSRs, we will turn CSRs into durable solids or soft rubbers by polymerization, and we will make hierarchical multi-core structures comprising cholesteric liquid crystals, from which highly interesting composite optical properties can be expected.
The second bottleneck is the lack of a solid understanding of CSR optics across the visible and near infrared spectra, for varying illumination and imaging conditions. ECLIPSE will deliver a systematic and thorough analysis of CSR optics filling this gap, combining experimental and numerical modeling (the latter supported by an external internationally leading theoretician specializing in the optics of periodic media with complex topologies). In addition to illuminating the situation of CSR photonics from a fundamental scientific point of view, this thrust will allow us to formulate design criteria for CSRs optimized in potential applications.

Figure 1: CSRs droplets (a) and shells (b–e) produce patterns that uniquely characterize the CSRs and their arrangements. The peripheral spots on sufficiently thick shells (b, d–e), lines in droplets (a), are due to photonic cross communication. The asymmetric shell in (c) allows light to enter inside, giving rise to internal reflection rings. Scale bar: 100 μm

Members:

Xu Ma (PhD candidate), Dr. Rijeesh Kizhakidathazhath (postdoc), Dr. Yong Geng (postdoc) & Prof. Jan Lagerwall (PI)

Collaborator:

Prof. Gerd Schröder-Turk, Murdoch University, Australia

Funding and duration:

This project was funded by the Fonds National de la Recherche Luxembourg (FNR) from 1 September 2021 through 31 August 2024.

Project blog:

01/09/2021 Our product start
14/01/2022 We organised an online CSR workshop together with Gabriele's group that working on computer science: security, reliability and trust.
04/08/2022 Prof.Gerd Schröder-Turk visited our group for one week.
01/10/2022 Dr.Yong Geng join the project.
25/10/2022 Our article: "Unclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors" published on Light: Science & Applications.