Wood is typically a hierarchical porous material with anisotropic structures and properties. For example, the anisotropic optical properties of wood are usually determined by its anisotropic structure. So far, the challenge remains in integrating anisotropic wood while achieving isotropic scattering performance. Moreover, wood porous scaffolds have not been fully utilized in research related to structure and molecular confinement relevant to optical properties. This project develops a luminescence-enhanced wood hydrogel by combining it with a three-dimensional N-isopropylacrylamide (NIPAM) polymer network and surface-carboxylated CdSe/ZnS quantum dots (QDs). Wood nanotechnology is applied to control the nanostructure of wood-based hydrogels, thereby realizing isotropic optical properties and mechanical reinforcement in luminescent wood hydrogels. This is related to the interstitial structure of the cellulose scaffold, which is reinforced by the NIPAM hydrogel polymer, where the surface carboxyl groups of the QDs are polarized and confined within the cellulose/NIPAM network. The luminescent properties of the functional hydrogel can be tuned by changing the temperature near the critical solution temperature of the NIPAM polymer. The constraint effects on the quantum dots at both molecular and structural domains in the wood-based hydrogels were studied. Furthermore, the functional hydrogel shows great potential for smart window applications, with optical modulation, energy-saving, and UV protection features. We envision that this functional wood hydrogel may find applications in bioimaging, flexible optics, smart sensors, and anti-counterfeit labels.

Summary:

A collaborative study by USTC and Nanjing Forestry University, published in ACS Nano, introduced a luminescent wood-based hydrogel (WH/QDs) with isotropic optical properties. The team created it by delignifying and alkali-treating balsa wood to preserve its honeycomb cell structure while introducing nanopores, then infused it with thermo-responsive PNIPAM and carboxylated CdSe/ZnS QDs via vacuum-assisted infusion, forming a 3D network through UV polymerization. This WH/QDs hydrogel exhibited enhanced photoluminescence due to synergistic nanoconfinement (pore physical restriction + molecular passivation via hydrogen bonds), tunable thermochromic luminescence, and improved mechanical strength, and showed potential for smart windows (transparent at <32°C for passive heating, opaque at high temperatures for solar blocking) with UV shielding, offering new insights for advanced functional wood materials.

Reference News:

DOI: 10.1021/acsnano.5c17173

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