Hydrophobic Fluorinated Polyurethane Encapsulants for Hydroacoustic Applications

Polyurethane elastomers are widely employed as underwater transducer encapsulants, owing to their distinctive mechanical and acoustic properties. However, the lack of hydrophobicity of polyurethanes remains a problem to be resolved. A series of hydrophobic fluorine-modified polyurethanes (FPUs) were synthesized by incorporating 1H,1H,2H,2H-perfluorodecyltriMethoxysilane (FAS-17) into polybutadiene-based polyurethane. These fluorinated chain extenders enhance the hydrophobicity by reducing surface energy and increase physical cross-linking points, thereby improving the material's overall performance. Remarkably, at a FAS-17 content of 4 wt%, the water contact angle of FPU-2 rises to 106.0°, with a water absorption rate of only 0.189%. This corresponds to a substantial 58.6% reduction in water absorption compared to unmodified polyurethane (PU), demonstrating its exceptional hydrophobicity. Additionally, the introduction of fluorine-containing chains enhances mechanical properties, with FPU-2 having an elongation at break (452%) and tensile strength (10.93 MPa). These results demonstrate that fluorinated polyurethane not only retains the essential properties for underwater sound transmission but also significantly improves hydrophobicity.