Preparation and property modulation of PVDF photonic crystal waterproof and breathable membrane with inverse opal structure

Introducing inverse opal structured photonic crystals into the field of waterproof and breathable membranes aims to break the game between moisture permeability and static water pressure resistance in porous waterproof and breathable membranes, thereby achieving high waterproof and breathable performance. Using silica (SiO₂) microspheres as template material and polyvinylidene fluoride (PVDF) as the filling material, a PVDF/SiO₂ composite photonic crystal film was prepared by shear induced assembly method. After removing the SiO₂ microspheres, PVDF photonic crystal waterproof and breathable film with inverse opal structure was obtained. The results show that inverse opal has a highly connected spherical porous structure, exhibiting characteristics such as uniform pore size and distribution, and well-developed pores, which meet the structural requirements of high static water pressure resistance and high moisture permeability porous membranes. The preparation of SiO₂ microspheres for inverse opal requires the condition of uniform particle size. The PVDF photonic crystal film with inverse opal structure prepared from SiO₂ microspheres with an average particle size of 280 nm has a thickness of 27.3 µm, an effective pore size of 41.4 nm and uniform distribution, a porosity of 68%, a static water contact angle of 125.7°, and hydrostatic pressure up to 92.6 kPa while ensuring mechanical properties. At the same time, the water vapor transmission rate (WVTR) is as high as 10.3 kg·m⁻²·d⁻¹, exhibiting excellent waterproof and moisture permeability. The waterproof performance can be controlled by adjusting the coating thickness, SiO₂ microsphere content, and SiO₂ microsphere particle size. This study provides a new approach for preparing waterproof and breathable membranes that balance moisture permeability and resistance to hydrostatic pressure.