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Due to their exceptional orientation of 2D nanofillers, layer-by-layer (LbL) assembled polymer/graphene oxide thin films exhibit unmatched mechanical performance relative to any conventionally produced counterparts with similar composition. Unprecedented mechanical property improvement, by replacing graphene oxide with pristine graphene, is demonstrated in this work. Polyvinylpyrrolidone-stabilized graphene platelets are alternately deposited with poly(acrylic acid) using hydrogen bonding assisted LbL assembly. Transmission electron microscopy imaging and the Halpin-Tsai model are used to demonstrate, for the first time, that intact graphene can be processed from water to generate polymer nanocomposite thin films with simultaneous parallel-alignment, high packing density, and exfoliation. A multilayer thin film with only 3.9 vol% of highly exfoliated, and structurally intact graphene, increases the elastic modulus (E) of a polymer multilayer thin film by 322% (from 1.41 to 4.81 GPa), while maintaining visible light transmittance of ≈90%. This is one of the greatest improvements in elastic modulus ever reported for a graphene-filled polymer nanocomposite with a glassy (E > 1 GPa) matrix. The technique described here provides a powerful new tool to improve nanocomposite properties (mechanical, gas transport, etc.) that can be universally applied to a variety of polymer matrices and 2D nanoplatelets.

Indentation of hydrated Nafion thin films reveals that both the in-plane diffusivity of water and the intrinsic permeability of the phase-segregated network decrease dramatically with decreasing film thickness. Using pore-network theory, this decrease in diffusivity is attributed to both an increase in ionic-domain heterogeneity and a reduction in ionic-domain connectivity upon confinement.

Nafi on nanocomposite membranes are attractive candidates for the ion conducting phase in energy storage devices such as vanadium redox fl ow batteries. Herein, vanadium crossover and Nafi on‐SiO 2 nanostructure are quantifi ed in a series of hybrid membranes created via solution-casting Nafi on fi lms with discrete SiO 2 nanoparticles, as well as membranes created using an in situ silica sol‐gel condensation process. The crossover of vanadium ions is suppressed in all Nafi on membranes with the SiO 2 inorganic phase when compared to unannealed, neat Nafi on membranes. However, it is also observed that annealing the neat Nafi on membranes is equally as effective at suppressing vanadium crossover. Small-angle neutron scattering measurements show that no signifi cant changes to the Nafi on structure occurred in membranes with discrete nanoparticles. In contrast, drastic changes in the scattering profi les of the Nafi on‐SiO 2 membranes created via sol‐gel chemistry are observed, where the SiO 2 nanoclusters are determined to be on the order of 10 nm in diameter. These scattering length scales are verifi ed through real space images using transmission electron microscopy. Insights from this investigation help elucidate the structure of the Nafi on‐SiO 2 membranes and suggest that the current hypothesis by how vanadium crossover is reduced may not be fully accurate.