Constructing Grape Bunch Structure Composite Film via Hollow AgNPs Coated Cellulose Nanofibers (CNF@PDA@H-AgNPs)/CNF for Efficient Electromagnetic Shielding, Thermal Conductivity, and Strain Sensing

Achieving high shielding effectiveness in electromagnetic shielding materials relies heavily on high conductivity, yet simultaneously enhancing the absorption loss remains a persistent challenge. Consequently, the study successfully creates efficient electromagnetic shielding composite films with a unique grape-like bunch structure of hollow nanosilver (HCAF) through layer-by-layer assembly. The utilization of poly(dopamine) (PDA) to anchor nanosilver granules (AgNPs) onto cellulose nanofibers (CNF) results in the formation of CNF@PDA@AgNPs. Subsequently, a surface protection etching method is employed to etch the AgNPs, resulting in hollow nanosilver (H-AgNPs) and the generation of CNF@PDA@H-AgNPs. A composite film featuring a grape bunch structure is fabricated by interweaving high aspect ratio CNF with CNF@PDA@H-AgNPs. A substantial quantity of H-AgNPs creates an abundant interface, while the grape bunch structure establishes an efficient conductive network. That enables the composite film to exhibit excellent impedance matching, excellent conductivity loss, abundant polarization loss, and multiple reflection loss. Therefore, the conductivity of the composite film with a thickness of 148.8 μm reaches 212660 S/m, with SE_{<i><i>T</i></i>}, SE_<i>A</i>, and SE_<i>R</i> 89.56, 79.03, and 10.53 dB in the X band, significantly better than the 76.9, 55.55, and 21.41 dB of the solid AgNPs composite film. The composite film also exhibits remarkable thermal conductivity (The coefficients of in-plane and out-plane thermal conductivity are 4.61 and 0.17 W/(m·K), respectively), mechanical properties, and strain sensing capabilities, making it significant potential for applications in flexible electronics and other related fields.