Cholesteric Spherical Reflectors with Tunable Color from Single-Domain Cellulose Nanocrystal Microshells

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Cellulose nanocrystals (CNCs) form cholesteric liquid crystal (CLC) films with wavelength- and polarization-selective Bragg reflection.
• These biosourced nanoparticles are promising for optical applications, but achieving spherical curvature has been challenging due to buckling in drying droplets.
• Spherical CLC structures could offer enhanced optical properties compared to flat films.

Purpose of the Study:

• To develop a method for creating spherical, single-domain cholesteric CNC particles.
• To overcome the buckling and shape instability issues encountered when drying CNC suspension droplets.
• To enable tunable retroreflection colors in spherical CNC particles for advanced optical applications.

Main Methods:

• Confining CNC suspensions within spherical microshells surrounding incompressible oil droplets.
• Utilizing the microshell confinement to prevent buckling and induce helix pitch compression during drying.
• Mixing different CNC types to tune the helical pitch and thus the retroreflection color.

Main Results:

• Successfully produced single-domain cholesteric spherical reflector particles with distinct visible colors.
• The confinement strategy prevented buckling and ensured spherical morphology.
• Spontaneous puncturing of the microshells allowed for oil extraction and recycling.
• Tunable retroreflection colors were achieved by varying CNC fractions, covering the visible spectrum.

Conclusions:

• A novel method enables the creation of spherically curved, single-domain cholesteric CNC particles.
• This approach overcomes previous limitations in fabricating spherical CLC structures from CNCs.
• The resulting particles offer excellent optical quality and tunable colors, expanding the utility of biosourced CLCs in optics.