Stable and Transparent Ca²⁺-Cross-Linked Alginate Composite Films for EMI Shielding and Joule Heating

Transparent electromagnetic interference (EMI) shielding materials can be used for specific optoelectronic applications. Herein, a uniform silver nanowire (AgNW) network was fabricated on a commercial polyimide film via a spraying method. The interconnected and effective conductive network with welded junctions was fastened onto a sodium alginate-based biopolymer substrate via rod-coating and -transferring methods to improve electrical conductivity and optical transmittance of composite films simultaneously. Moreover, another SA-based layer was coated to encapsulate the AgNW network firmly, followed by cross-linking with calcium ions (Ca²⁺), enabling the CA-based barrier to protect the nanowires from corrosion by moisture and oxygen in the air. Consequently, the obtained flexible CA/AgNWs/CA composite film achieved a satisfactory EMI shielding effectiveness of 27.9 dB with a favorable optical transmittance of 72.8% at 550 nm. Furthermore, the composite film also showed excellent Joule heating performance with a sensitive thermal response and good stability. The CA/AgNWs/CA composite film retained a stable EMI shielding efficiency after being exposed to air for 20 days with a slight decline in EMI SE upon cyclic bending deformation and thermal shock treatment several times because of the compact sandwich-like structure and cross-linked CA-based barrier. Thus, the flexible and transparent CA/AgNWs/CA composite film holds great promise for practical applications in optical electronic devices.