Robust and smart underwater adhesion of hydrophobic hydrogel by phase change

Water-durable adhesives are widely explored in various fields like wearable electronics, tissue engineering and sea refloatation. However, in harsh underwater environment, adhesives with sound and comprehensive performance on various surfaces remain highly challenging. Herein, we report a hydrophobic hydrogel adhesive composed of crystalline octadecyl (C18) chains with versatile, robust and thermally switchable underwater adhesion. The inherent hydrophobicity and the amorphous state of C18 chains allow the hydrogel adhesive to conformally adapt to underwater surfaces, independent of surface energy, curvature, charge and roughness as well as the salinity and pH of the water environment. The crystallization of C18 chains greatly increases the modulus of the hydrogel, interlocking the adhesive to the contacting surfaces and resulting in the underwater adhesion up to 275 kPa. The phase change of hydrogel regulates the stress distribution at the contact interface and the adhesion capacity, resulting in a switchable underwater adhesion. The phase change of C18 chains also endows the hydrogel self-healing property, ensuring durability and reusability. Moreover, the temperature of phase change is around ∼ 40 ℃, endowing adhesive with bio-applications in dynamic watery environments. Therefore, the adhesive is highly potential in emerging areas of wearable electronics, tissue engineering and so on.