A Millimeter-Thick Photoresponsive Polymer Enabling In-Plane Compression Modulation for Tactile Displays

In this study, a millimeter-thick photoresponsive polymer capable of dynamic viscoelastic modulation under blue light irradiation is reported. This star-shaped polymer has a polydimethylsiloxane (PDMS) backbone networked via photoresponsive hexaarylbiimidazole (HABI) and is referred to as PDMS–HABI. By controlling the molecular weight of the PDMS precursor, the density of HABI was tuned, thereby enabling light penetration and photoresponse in samples with thicknesses up to 2 mm. Compression tests revealed that transmittance played a more crucial role than the local elastic modulus in determining the extent of compression force reduction upon light irradiation. The optimized sample exhibited a compression force reduction to 1/28 under 430 nm light irradiation. To explore practical applications, we fabricated a tactile display capable of presenting hard and soft sensations. However, as PDMS–HABI lacked shape recovery when exposed to light, it was integrated into an elastic container to endow it with resilience. The compression properties of the container filled with PDMS–HABI were evaluated under light irradiation, and photoinduced softening reduced the compression force by nearly 50%. These results indicated the feasibility of using PDMS–HABI in tactile displays capable of presenting in-plane distributions of hardness and softness with potential applications in augmented reality/virtual reality haptic interfaces.