Hydrophilic coatings and films

Diffusion of water vapour through a solid film is achieved by the incorporation of hydrophilic, or water attracting, functional groups along the molecular chain which can form reversible "hydrogen bonds" with water molecules. These bonds are comparatively weak and can be readily broken down by thermal motion.

Water molecules diffusing through the film pass stepwise along the molecular chains, a process which is facilitated by introducing pendant side-groups, which prevent close-packing of adjacent chains. The passage of water molecules through solid films is such that the rate of diffusion is proportional to the concentration gradient of water vapour between the two surfaces of the film.