title: Polymer reinforcement using liquid-exfoliated boron nitride nanosheets.
abstract: We have exfoliated hexagonal boron nitride by ultrasonication in solutions of polyvinylalcohol in water. The resultant nanosheets are sterically stabilised by adsorbed polymer chains. Centrifugation-based size-selection was used to give dispersions of nanosheets with aspect ratio (length/thickness) of ∼1400. Such dispersions can be used to produce polyvinylalcohol-BN composite films. Helium ion microscopy of fracture surfaces shows the nanosheets to be well dispersed and the composites to fail by pull-out. We find both modulus, Y, and strength, σ(B), of these composites to increase linearly with volume fraction, V(f), up to V(f)∼ 0.1 vol% BN before falling off. The rates of increase are extremely high; dY/dV(f) = 670 GPa and dσ(B)/dV(f) = 47 GPa. The former value matches theory based on continuum mechanics while the latter value is consistent with remarkably high polymer-filler interfacial strength. However, because the mechanical properties increase over such a narrow volume fraction range, the maximum values of both modulus and strength are only ∼40% higher than the pure polymer. This phenomenon has also been observed for graphene-filled composites and represents a serious hurdle to the production of high performance polymer-nanosheet composites.
authors.affiliation: Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) & School of Physics, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Umar
authors.initials: U
authors.lastname: Khan
authors.forename: Peter
authors.initials: P
authors.lastname: May
authors.forename: Arlene
authors.initials: A
authors.lastname: O'Neill
authors.forename: Alan P
authors.initials: AP
authors.lastname: Bell
authors.forename: Elodie
authors.initials: E
authors.lastname: Boussac
authors.forename: Arnaud
authors.initials: A
authors.lastname: Martin
authors.forename: James
authors.initials: J
authors.lastname: Semple
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Coleman