▎ 摘　　要

We have prepared polymer-graphene composites from sonication-exfoliated graphene. Using centrifugation-based size selection, we prepared composites using flakes of two different aspect ratios, similar to 1000 and similar to 2000. We find very little reinforcement using the smaller flakes. However, the larger flakes result in a doubling in modulus and strength for <0.4 vol% graphene. We show these results to be in line with theory which predicts a sharp increase in reinforcement efficiency as the aspect ratio is increased from 1000 to 2000. The observed reinforcement exactly matches that expected for the measured flake size and is within 30% of the ultimate limit.