Substrate Engineering for Durable Omniphobic Liquid‐Like Surfaces

Abstract The critical role of substrates in enhancing the omniphobicity of liquid‐like surfaces (LLSs) is investigated. To smoothen substrate asperity roughness and graft polydimethylsiloxane (PDMS)‐based LLSs, sol–gel silica utilizing 1,2‐bis(triethoxysilyl)ethane (BTESE) and incorporating non‐ionic surfactants is developed, achieving crack‐free thicknesses of 28 µm, a ≈100 × improvement over synthesis using tetraethoxysilane. Substrate surface silanol density significantly impacts the final wetting behavior, and a silanol density ≤ 1.43 nm − 2 is inadequate for achieving minimal contact angle hysteresis (CAH). Oxygen plasma treatment of BTESE silica increases the silanol density to 2.28 nm − 2 , resulting in omniphobicity, including a 2° CAH with water and < 1° CAH for decane, octane, and toluene. The mechanical properties of substrates influence the abrasion resistance of PDMS‐LLSs, with two distinct abrasion damage modes identified: 1) removal or cleavage of PDMS chains, which is independent of the substrate material, and 2) substrate scratching without removing the surrounding PDMS, leading to a rapid loss of liquid‐repellency, particularly on softer silica substrates. A bilayer silica system formed from two different organosilica precursors is then developed to smoothen rough substrates without sacrificing durability. These findings extend the application of PDMS‐LLSs to a range of substrates and offer insights in engineering damage‐tolerant LLSs.