Dual cross-linked MXene/cellulose nanofiber/nickel alginate film with improved mechanical properties and electromagnetic interference shielding performance

Electromagnetic interference pollution has raised urgent demand for the development of electromagnetic interference shielding materials.Transition metal carbides(MXenes)with excellent conductivity have shown great potential in electromagnetic interference(EMI)shielding materials,while the poor mechanical strength,flexibility,and structural stability greatly limit their further applications.Here,cellulose nanofibers and sodium alginate are incorporated with MXene nanosheets as flexible matrices to construct strong and flexible mussellike layered MXene/Cellulose nanofiber/Sodium Alginate composite films,and nickel ions are further introduced to induce metal coordination crosslinking of alginate units.Benefited from the dual-crosslinked network structure of hydrogen bonding and metal coordination,the tensile strength,Young’s modulus,and toughness of the MXene/cellulose nanofiber/nickel alginate composite film are significantly increased.After subsequent reduction by ascorbic acid,excess nickel ions are reduced to nickel nanoparticles and uniformly dispersed within the highly conductive composite film,which further improved its hysteresis loss effect toward the incident electromagnetic waves.Consequently,the MXene/cellulose nanofiber/nickel alginate-Ni composite film presents a considerably enhanced electromagnetic interference shielding effectiveness(47.17 dB)at a very low thickness of 29μm.This study proposes a feasible dual-crosslinking and subsequent reduction strategy to synergistically enhance the mechanical properties and electromagnetic interference shielding performance of MXene-based composite materials.

Research on vibration suppression of a mistuned blisk by a piezoelectric network

The work aims to provide a further investigation of the dynamic characteristics of an integral bladed disk（also called ‘blisk＇） with a Parallel Piezoelectric Network（PPN）. The PPN is constructed by parallelly interconnecting the piezoelectric patches distributed in the blisk. Two kinds of PPN are considered, namely mono-periodic PPN and bi-periodic PPN. The former has a piezoelectric patch in each sector, and the later has one patch every few sectors. The vibration suppression performance of both kinds of PPN has been studied through modal analysis, forced response analysis, and statistical analysis. The research results turn out that the PPN will only affect mechanical frequencies near the electrical frequency clusters slightly, and the bi-periodic PPN will make the nodal diameter spectrum of the modes more complex, but the amplitude corresponding to the new nodal diameter component is much smaller than that of the nodal diameter component corresponding to the mono-periodic system. The mechanical coupling between the blades and the disk plays an important role in the damping effect of the PPN, and it should be paid attention to in applications. The mono-periodic PPN can effectively suppress the amplitude magnification of the forced response induced by the mistuning of the blisk; meanwhile, it can mitigate the vibration localization of the mistuned electromechanical system. If piezoelectric patches are set only in part of the sectors, the bi-periodic PPN still has a vibration suppression ability, but the effect is related to the number and spatial distribution of the piezoelectric patches.