Large-Diameter Silica Nanosheets for Self-Assembly into Composite Films

The nacre-inspired "brick-and-mortar" structure is used to prepare materials with high strength, toughness, and barrier performance by setting geometric parameters, such as the diameter, thickness, and aspect ratio of the assembly blocks. However, there have been no reports of large-diameter "bricks". Herein, we report the synthesis of silica nanosheets with ∼20 μm diameter and adjustable aspect ratios using anionic and cationic surfactant micelle templates, and the self-assembly of the nanosheets was assisted by a heat pressing process to form ethyl cellulose (EC) composite films. Such a large-block brick-and-mortar structure has significantly improved the various properties of the composite films, including increasing the strength and Young's modulus of the EC films by 160 and 429%, respectively, maintaining 97% transparency (with a content of 50 wt % silica nanosheets), and increasing gas barrier performance by 120 times. We establish comprehensive relationships among the high performance of nacre-inspired films and the diameter and aspect ratio of the nanosheets, which will pave the way for the practical application of flexible optical barrier films.