Robust alternating multilayered cellulose nanofiber composite membranes fabricated by high-efficiency calcium ion-precomplexed vacuum-assisted self-assembly towards electromagnetic interference shielding

One-dimensional cellulose nanofiber (CNF) is prone to constructing connected nanofiber networks in vacuum-assisted self-assembly due to intense hydrogen bonds, which exhibits great superiority in fabricating electromagnetic interference (EMI) shielding composite membranes. However, time-consuming vacuum-assisted assembly process creates vast bottlenecks for spreading EMI shielding CNF composites. Herein, a Calcium ion (Ca2+)-precomplexed vacuum-assisted self-assembly strategy is first proposed to high-efficiently assemble robust CNF&Carbon nanotube/Polyethylene oxide (CNF&CNT/PEO) composite membranes with alternating multilayer architectures. The introduction of Ca2+ pre-complexation can not only largely improve the fabrication efficiency but also immensely enhance the mechanical properties of alternating multilayered CNF&CNT/PEO membranes. The self-assembly time of CNF-5&CNT/PEO-4 is greatly decreased to 756 min at 0.45 mmol/L Ca2+, in comparison with the common vacuum-assisted filtration (i.e., without Ca2+) of 1192 min, owing to the hydrogen bonds between CNF and water broken down by Ca2+ complexation in aqueous dispersion. With the Ca2+ concentration increasing from 0 to 0.23 further to 0.45 mmol/L, the tensile strength of CNF-3&CNT/PEO-2 is gradually reinforced from 40.2 to 43.2 and to 47.6 MPa, as a consequence of the excellent Ca2+ crosslinking and hierarchical "Zigzag" crack paths. The favorable electrical conductivity and unique alternating multilayered structures endow CNF-5&CNT/PEO-4 membrane with the maximal EMI shielding effectiveness (SE) of 43.3 dB. The Ca2+-precomplexed strategy sheds new light on high-efficient self-assembly of multilayered CNF composite membranes with pretty EMI shielding performances, which has prospective application in advanced electronics and microelectronic packaging.