What is photo-induced hydrophilicity?

Self-Cleaning Surfaces

The charged particles left on a surface by photocatalysis promote a water-loving or hydrophilic surface. This allows water to sheet evenly, promoting self cleaning characteristics.

The coated surface does not repel water at all, so water cannot exist in the shape of a drop, but spreads flatly on the surface of the substrate. And the water took the form of a highly uniform thin film, which behaves optically like a clear sheet of glass.

When Titanium Dioxide is exposed to light, its surface exhibits superhydrophilicity, with water contact angles of 5° or less. Although the underlying mechanism is again the formation of electron-hole pairs under light irradiation, the superhydrophilicity is directly the result of the formation of oxygen vacancies by the interaction of holes with oxygen atoms in the crystalline lattice. Such defects form a hydrophilic domain, and since water is easily adsorbed there, general superhydrophilicity results.

Organic Decomposition and Creation of Hydrophilicity
Photocatalytic decomposition weakens the ability of oil to adhere to a surface. The result is that rainwater spreads uniformly over the surface and floats away grime, for a self-cleaning functionality. These superhydrophilic properties give rise to an antifogging effect. In addition, when surfaces coated with a Titanium Dioxide photocatalyst are exposed to contaminants such as oil, the combination of superhydrophilicity and oxidative decomposition leads to the contamination being washed away by rain water.

Hydrophobic vs. Hydrophilic

A regular glass surface, after it is cleaned or coated with hydrophobic solution, exhibits hydrophobicity, meaning that the contact angle is high. This causes water to bead up and spot, making the glass harder to clean.

Hydrophilic glass, like glass coated with Lumactiv, has a low contact angle. When water comes into contact with the photocatalytic surface, it spreads out across the glass. It evaporates more quickly, which translates into fewer water spots on your windows. Your windows will stay cleaner and brighter for a longer period of time.