Structural Multi-Colour Invisible Inks with Submicron 4D Printing of Shape Memory Polymers

TL;DR

This paper demonstrates submicron 4D printing of shape memory polymers with multi-colour capabilities, enabling reversible invisibility and colour tuning for applications in anti-counterfeiting and photonics.

Contribution

It introduces a new high-resolution SMP photoresist compatible with two-photon polymerization, enabling nanoscale 4D printing with reversible colour and shape memory effects.

Findings

Achieved ~300 nm resolution in 4D printing of SMPs.

Demonstrated reversible colour and shape changes upon heating.

Enabled potential applications in anti-counterfeiting and tunable photonics.

Abstract

Four-dimensional (4D) printing of shape memory polymer (SMP) imparts time responsive properties to 3D structures. Here, we explore 4D printing of a SMP in the submicron length scale, extending its applications to nanophononics. We report a new SMP photoresist based on Vero Clear achieving print features at a resolution of ~300 nm half pitch using two-photon polymerization lithography (TPL). Prints consisting of grids with size-tunable multi-colours enabled the study of shape memory effects to achieve large visual shifts through nanoscale structure deformation. As the nanostructures are flattened, the colours and printed information become invisible. Remarkably, the shape memory effect recovers the original surface morphology of the nanostructures along with its structural colour within seconds of heating above its glass transition temperature. The high-resolution printing and excellent reversibility in both microtopography and optical properties promises a platform for temperature-sensitive labels, information hiding for anti-counterfeiting, and tunable photonic devices.