posted on 2025-02-05, 00:43authored byIrina Zubritskaya, Daniele Martella, Sara Nocentini
Materials that can visually report changes in the surrounding
environments
are essential for future portable sensors that monitor temperature
and detect hazardous chemicals. Ideal responsive materials for optical
sensors are defined by a rapid response and readout, high selectivity,
the ability to operate at room temperature, and simple microfabrication.
However, because of the lack of viable materials and approaches, compact,
passive, and multipurpose practical devices are still beyond reach.
To address this challenge, we develop a methodology to fabricate colored
and responsive micropixels printed by digital light projection lithography
on gold substrates. These structures are made by polymeric Liquid
Crystalline Networks (LCNs) whose birefringence and external stimuli
responsiveness allow for micrometric devices with visual and fast
response that we here apply to a few applications. First, we show
how varying the projected geometrical shape can become an effective
tool to engineer symmetric disclination lines in the liquid crystal
order. Depending on the thickness of the micropixels, LCNs give rise
to a birefringence color under polarized light or a structural color
under white light due to thin-film interference. By exposing the micropatterns
to temperature variation and solvents, we demonstrate a real-time
optical temperature detection and differentiation between selected
organic chemicals. The proposed materials and fabrication method could
be scaled up and extended to roll-to-roll printing, enabling future
real-life applications of liquid crystalline polymers in affordable
microdevices and optical sensors with a net advantage with respect
to traditional lithographic techniques in terms of fabrication speeds
and costs.