Waterproof membranes, also known as antifouling membranes or hydrophobic and oleophobic membranes, are functional thin film layers with oil and water resistance. When deposited as a top layer on the surface of an antireflective film to form a composite film system, their thickness can be as thin as 0.005-0.01 mm without altering the optical properties of the antireflective film. These membranes are often prepared using vacuum deposition processes, achieving contact angles up to 110 degrees.
Their working principle is based on reducing the surface micro/nano structure to minimize the area for dirt adhesion. The antifouling membrane covers the porous antireflective film layer and reduces the contact area between water and oil and the lens, making it difficult for oil and water droplets to adhere to the lens surface. When water falls on the filter surface, it slides off quickly, much like water falling on a lotus leaf.
Another principle is to achieve barrier protection through the formation of a physical barrier by the material. This can be achieved through microphase separation structures (such as the 0.1-10 μm micropores of TPU films) or surface lotus leaf effect coatings (contact angle > 150°), blocking liquid water while maintaining breathability. TPU is a block copolymer composed of polyols, diisocyanates, and chain extenders. Based on the type of soft segments, it can be classified into polyester-type TPU, polyether-type TPU, and polycarbonate-type TPU. To improve barrier properties, blending, coating, multilayer composite, and nanofilling methods are commonly used. Polyvinylidene fluoride (PVDF) fluorocarbon membranes achieve weather resistance and waterproofing due to their excellent chemical stability.
In terms of technological development, China has mass-produced fluorine-free waterproof membranes. Through self-developed high-moisture-wicking bio-based polymers and fluorine-free water-repellent modification, high-performance waterproof and breathable membranes have been achieved without adding organic fluorine compounds.
