Transparent, flexible composites that merge inorganic and organic characteristics are essential for advancing adaptive optics, bio‑integrated sensing, and reconfigurable photonics. However, a long‑standing barrier has been the intrinsic trade‑off between mechanical flexibility and broadband infrared (IR) transmission. IR transparency typically requires rigid, heavy‑atom networks to suppress multi‑phonon absorption, while flexibility demands soft, dynamically bonded molecular chains that unfortunately exhibit strong IR absorption. This inherent conflict has left a critical gap for emerging technologies such as IR adaptive optics, which demands compact, high‑performance systems capable of real‑time wavefront correction: organic‑based deformable lenses lack sufficient IR transparency, whereas reflective mirror systems are bulky and optically complex. There is therefore a pressing need for a new class of truly “IR‑transparent yet flexible” materials.
In a new paper published in Light: Science & Applications , a team of scientists, led by Professor Changgui Lin from Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies, Ningbo University, Ningbo 315211, China, and co-workers have developed a S 60 Se 40 chalcogenide glass with a unique chain-ring dual-network (DN) architecture that directly overcomes the long‑standing trade‑off. By integrating heavy chalcogen elements (S, Se) with a dynamic covalent network of physical crosslinks, this DN material simultaneously yields an ultralow Young’s modulus (≈0.0037 GPa), extreme tensile strain (≈650%), high elastic recovery (≈80%), and autonomous self‑healing at room temperature, while maintaining an ultra‑broad transmission window from 0.62 μm to 21 μm, fully covering the important 3-5 μm and 8-14 μm atmospheric windows. The physically cross‑linked DN structure, composed of covalent [Se, S] n chains interwoven with dynamic S 8-y Se y rings, enables ultralow modulus, large deformations and high elastic recovery through reversible chain straightening, slippage, and bond exchange.
Based on this novel material, the team developed plano‑concave and plano‑convex IR deformable lenses using fused deposition modelling followed by optical polishing. Under multi‑axial mechanical strain, the lenses achieved a focal tuning range of over 11% with linear response, outperforming conventional elastomeric lenses. Imaging experiments demonstrated reversible focal switching, depth‑of‑field modulation, and high‑quality IR imaging even after cyclic stretching.
“The origin of this unprecedented combination lies in the dual‑network’s dynamic behavior. Molecular dynamics simulations reveal that under tension, the polymeric chains elongate and slip, whereas the rings act as mobile topological crosslinkers that dissipate stress without fracture. In situ Raman spectroscopy shows reversible bond elongation of Se-Se chains, underpinning the hyperelastic response. The low glass transition temperature (13.5 °C) and dynamic covalent bonds (S-S, Se-Se, Se-S) further enable room‑temperature self‑healing” they added.
“This work bridges the gap between glass‑like optical performance and polymer‑like mechanics. The S 60 Se 40 glass not only provides a practical solution for IR adaptive optics including compact deformable lenses but also opens a new material platform for soft IR photonics, bio‑integrated sensing, and reconfigurable optical systems that require both broad spectral transparency and mechanical compliance” the scientists forecast.
Light: Science & Applications
An infrared-transparent flexible glass for adaptive optics