Constructing Grape\nBunch Structure Composite Film\nvia Hollow AgNPs Coated Cellulose Nanofibers (CNF@PDA@H-AgNPs)/CNF\nfor Efficient Electromagnetic Shielding, Thermal Conductivity, and\nStrain Sensing

Achieving high shielding effectiveness in electromagnetic\nshielding\nmaterials relies heavily on high conductivity, yet simultaneously\nenhancing the absorption loss remains a persistent challenge. Consequently,\nthe study successfully creates efficient electromagnetic shielding\ncomposite films with a unique grape-like bunch structure of hollow\nnanosilver (HCAF) through layer-by-layer assembly. The utilization\nof poly(dopamine) (PDA) to anchor nanosilver granules (AgNPs) onto\ncellulose nanofibers (CNF) results in the formation of CNF@PDA@AgNPs.\nSubsequently, a surface protection etching method is employed to etch\nthe AgNPs, resulting in hollow nanosilver (H-AgNPs) and the generation\nof CNF@PDA@H-AgNPs. A composite film featuring a grape bunch structure\nis fabricated by interweaving high aspect ratio CNF with CNF@PDA@H-AgNPs.\nA substantial quantity of H-AgNPs creates an abundant interface, while\nthe grape bunch structure establishes an efficient conductive network.\nThat enables the composite film to exhibit excellent impedance matching,\nexcellent conductivity loss, abundant polarization loss, and multiple\nreflection loss. Therefore, the conductivity of the composite film\nwith a thickness of 148.8 μm reaches 212660 S/m, with SE<sub><i><i>T</i></i></sub>, SE<sub><i>A</i></sub>, and SE<sub><i>R</i></sub> 89.56, 79.03, and 10.53\ndB in the X band, significantly better than the 76.9, 55.55, and 21.41\ndB of the solid AgNPs composite film. The composite film also exhibits\nremarkable thermal conductivity (The coefficients of in-plane and\nout-plane thermal conductivity are 4.61 and 0.17 W/(m·K), respectively),\nmechanical properties, and strain sensing capabilities, making it\nsignificant potential for applications in flexible electronics and\nother related fields.