Morphology of Hydrophilic and Hydrophobic Domains are the Key to Improve Fouling Release of Polyurethane Coatings

Soft polyurethane fouling‐release coatings are modified with synthesized mPEG‐305, a hydrophilic PEG‐based additive, and a commercially hydrophobic PDMS‐based additive by click chemistry to generate hydrophilic and hydrophobic surface domains. Sessile drop contact angle measurements reveal polarity gradients ranging from ∆Ө = -32° to ∆Ө = 120°. AFM and SEM demonstrate successful additive incorporation (hydrophilic and hydrophobic additive addition of 2.5-20 mol% and 5–15 mol%) and the formation of two‐phase systems with microstructures, including spherical hydrophobic and characteristic “wrinkled” morphologies. Captive bubble contact angle measurements of systems with “wrinkled” microstructures indicate dynamically hydrophilic behavior, with contact angle changes of up to 15° over 33 days of immersion in demineralized water. Static immersion tests in the North Sea (Helgoland) for 18 weeks demonstrate enhanced bio‐repulsivity, with LoF values decreasing from 4 to 2-3 for systems with the strongest polarity gradient (∆Ө = 112°-120°), additive contents of 5-10 mol%, dominant wrinkled microstructures with pronounced stiffness (5 Pa) and topographical (100 nm) gradients, and dynamically hydrophilic contact angles changes of 15°. This highlights the critical influence of polarity gradients, microstructural heterogeneity and dynamic hydrophile behavior on the bio‐repulsivity of polyurethane coatings.