Fully Aqueous and Printable Photonic Inks with Tunable Pitch and Optical Memory via Hydrogen-Bonded HPC-PVA Networks

Area of Science:

• Materials Science
• Polymer Chemistry
• Optics

Background:

• Achieving rewritable, structurally colored biopolymer coatings requires aqueous processing, tunable optics, and dry-state color retention, often necessitating chemical crosslinking.
• Existing hydroxypropyl cellulose (HPC)-based inks face limitations in reconciling these properties due to intrinsic material constraints.

Purpose of the Study:

• To develop a fully water-based, compositionally programmable photonic ink using a non-covalent approach.
• To overcome the limitations of traditional biopolymer coatings by leveraging competitive hydrogen bonding for dynamic pitch modulation and kinetic trapping of cholesteric order.

Main Methods:

• Blending hydroxypropyl cellulose (HPC) with poly(vinyl alcohol) (PVA) additives of varying molecular weights and hydrolysis degrees.
• Utilizing competitive hydrogen bonding between HPC and PVA to control cholesteric pitch and achieve kinetic arrest via thermal annealing.
• Characterizing the resulting ink formulations for optical properties, rheology, and printability using direct ink writing.

Main Results:

• Formulations exhibited continuously adjustable structural colors (466-633 nm) and high yield stress (>100 Pa) with shear-thinning behavior suitable for direct ink writing.
• Thermal annealing enabled kinetic arrest of the cholesteric structure without covalent crosslinking, resulting in vibrant dry-state color and mechanical integrity.
• Printed films demonstrated humidity-responsive reversible color shifts (up to 240 nm) and rewritable optical memory, even in 3D structures.

Conclusions:

• A non-covalent design paradigm was established for biopolymer photonic inks, integrating pitch programmability, environmental responsiveness, and printability.
• This approach offers a scalable and sustainable route toward advanced photonic coatings and rewritable optical devices.
• The developed ink overcomes the need for chemical crosslinking, enabling versatile applications in tunable color and optical data storage.