Underwater Superoleophobic and Transparent Films with Mechanical Robustness and High Durability in Harsh Environments

Underwater superoleophobic and transparent (UST) films are promising in applications, such as advanced optical devices in marine environments. However, the mechanical robustness and durability in harsh environments of the existing UST films are still unsatisfactory. In this work, we present a free-standing nacre-inspired mineralized UST (NIM-UST) film with high aragonite content and excellent mechanical properties toward robust underwater superoleophobicity on two surfaces and transparency (94%) in harsh seawater environments. Such NIM-UST films were fabricated by using a simple and effective magnesium ion (Mg²⁺)-assisted dual-side mineralization strategy. The NIM-UST films exhibit high inorganic content (87 wt %), among which the aragonite fractions can reach 98 wt %. As a result, the modulus and hardness of the resulting NIM-UST films increased by 154% (from 8.17 ± 0.37 GPa to 20.78 ± 0.94 GPa) and 190% (from 0.70 ± 0.02 GPa to 2.03 ± 0.08 GPa), respectively, compared to those of the single-side NIM-UST films. And both surfaces of the resulting NIM-UST film maintain excellent underwater superoleophobicity (oil contact angle > 150°) and low oil adhesive force (<4 μN) under conditions of high-salt solutions, high temperatures, long-term immersion in seawater, and sand shock. In addition, the NIM-UST films can also be assembled into bulk materials with high hardness (2.63 ± 0.03 GPa) and flexural strength (109.55 ± 5.91 MPa) as next-generation structural materials. The feasible strategy developed in this work can promote the development and practical application of NIM-UST films.