Grayscale Photomasks Enable Noncontact Optical Patterning of Hydroxypropyl Cellulose Gels for Dynamic Art

ABSTRACT Hydroxypropyl cellulose (HPC) forms cholesteric photonic gels with dynamic structural color, but most HPC systems are tuned globally or patterned through serial fabrication. Here we report a mask‐encoded parallel photonic manufacturing strategy that locally regulates the reflected wavelength of acrylamide‐containing HPC (AM‐HPC) photonic gels. UV‐induced photopolymerization produces a dose‐dependent blueshift consistent with cholesteric‐pitch compression, yielding a 204 nm (662–458 nm) tuning window in 68 wt.% AM‐HPC under time‐controlled exposure and spatial features down to 50 µm. To translate this response into programmable manufacturing, we combine Gaussian‐process active‐learning calibration with an experimentally measured mask‐opacity‐to‐UV transfer function. This workflow converts two‐dimensional target wavelength fields into grayscale optical masks, enabling spatially varying UV doses to be delivered simultaneously across a continuous, unsegmented gel. A single 10 s exposure produced multilevel structural‐color images with an 85 µm mask‐pixel pitch (13 840 pixels cm − 2 ) in a continuous gel. The patterned gels retain thermally responsive structural color, allowing dynamic modulation of encoded images. These results establish a proof‐of‐concept digital‐to‐material workflow for parallel, composition‐specific programming of apparent structural color in continuous HPC photonic gels.