Recent experimental studies have demonstrated that the introduction of oxygen-containing functional groups in graphene sheets can greatly enhance the mechanical properties of their nanocomposites with polar polymers even at extremely low loadings. Motivated by these reports, we determine here the elastic constants of syndiotactic poly(methyl methacrylate) (sPMMA) at small wt % loadings of graphene sheets through atomistic modeling. To carry out a comparative study of the effect of graphene functionalization on the degree of mechanical reinforcement, we address both pure (i.e., unfunctionalized) and functionalized graphene sheets bearing epoxy and hydroxyl groups randomly bound on both sides of their surface in the host sPMMA matrix. The calculation of elastic constants (which involves no adjustable parameters) follows the methodology originally proposed by Theodorou and Suter [Macromolecules198619139], and has been based on the use of the Dreiding all-atom force-field. Our predictions for the elastic constants (which for the pure sPMMA matrix are within the error bars of experimentally computed values) suggest a substantial increase in the elastic constants, especially in the case of functionalized graphene sheets. For example, at just 5.67 wt % loading of the host matrix in functionalized graphene sheets, they indicate an improvement in Young’s modulus E by ∼74%, in the bulk modulus B by ∼19%, and in the shear modulus G by 83%. Our results fully corroborate recent experimental measurements about the unique opportunities that functionalized graphene sheets offer for the design of new, very strong multifunctional materials at low nanofiller content.

Piezoelectric fluoropolymers convert mechanical energy to electricity and are ideal for sustainably providing power to electronic devices. To convert mechanical energy, a net polarization must be induced in the fluoropolymer, which is currently achieved via an energy-intensive electrical poling process. Eliminating this process will enable the low-energy production of efficient energy harvesters. Here, by combining molecular dynamics simulations, piezoresponse force microscopy, and electrodynamic measurements, we reveal a hitherto unseen polarization locking phenomena of poly(vinylidene fluoride–co–trifluoroethylene) (PVDF-TrFE) perpendicular to the basal plane of two-dimensional (2D) Ti3C2Tx MXene nanosheets. This polarization locking, driven by strong electrostatic interactions enabled exceptional energy harvesting performance, with a measured piezoelectric charge coefficient, d33, of −52.0 picocoulombs per newton, significantly higher than electrically poled PVDF-TrFE (approximately −38 picocoulombs per newton). This study provides a new fundamental and low-energy input mechanism of poling fluoropolymers, which enables new levels of performance in electromechanical technologies.

High-performance, unpoled and recyclable piezoelectric generators are produced by combining dipole templating via single-walled carbon nanotubes with shear-induced polarisation via 3D printing of fluoropolymers.