Interfacial Skeleton Strengthening Mechanism of Porous Polymer Coating under Deep-Sea Alternating Hydrostatic Pressure.

With the advancement of deep-sea exploration and marine energy extraction, lightweight alloy equipment such as unmanned underwater vehicles and deep-submergence vehicles must be capable of withstanding increasingly severe alternating hydrostatic pressure (AHP) during descent and recovery. However, rigid microarc oxidation coatings are prone to interfacial failure due to their excessive elastic modulus. Herein, a porous organic-organic coating was fabricated, exhibiting a thickness of approximately 35 μm, a porosity of 21%, and a water contact angle of 135°. After 120 cycles of AHP (0-40 MPa), the coating initially underwent densification (thickness decreased by 10.4% and porosity by 16.29%) to enhance the yield strength of the flexible skeleton, then entered a stable service plateau where variations in thickness and porosity remained below 3%. Thus, an interfacial mechanical evolution model for porous organic-organic coatings was established. By integrating the effective stress principle, a "skeleton strengthening" design criterion was proposed based on operating pressure (P), skeleton yield limit (σy), and initial porosity (η). This criterion was validated by the phase interface failure observed in porous inorganic-organic coatings under AHP, providing guidance for the engineering design of pressure-resistant materials.