Self-cleaning surfaces could be used for smartphone screens

A team from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB are investigating the use of titanium-dioxide molecules incorporated into the surface of materials, which gives them self-cleaning properties.

When titanium-dioxide molecules are activated by the Sun’s UV light they act as a catalyst, triggering an electrochemical reaction that produces free radicals (atoms with unpaired electrons).

These and other active molecules have the ability to kill off bacteria, fungi and similar organisms. Initially, they destroy the cell walls and then penetrate the cytoplasm and damage the cell’s DNA. As a result, the organic substances are destroyed instead of remaining stuck to the surface.

‘We ran some outdoor tests on garden-chair armrests with photocatalytic coatings and compared them to ones made from conventional plastics,’ said Dr Iris Trick, group manager at IGB in Stuttgart.

Dr Trick and her team sprayed the coated and uncoated armrests with a mixture of various bacteria, mosses, algae and fungi and then left them exposed to the weather for two years.

It was almost impossible to remove the layer of dirt from the normal armrests while the armrests made from photocatalytic plastics remained almost completely clean.

The researchers also tested the coatings’ effectiveness on a range of other surfaces in the lab. This involved applying up to 30 different kinds of fungal, bacterial and algal cultures to coated and uncoated surfaces and comparing how the cultures evolved.

Following on from this research, teams in other departments adapted the coating so that it could be used on other surfaces.

Researchers from the Fraunhofer Institute for Manufacturing, Engineering and Automation IPA in Stuttgart are working on paints for building facades that contain titanium-dioxide particles.

Other colleagues have developed a self-cleaning coating for glass surfaces that requires an hour’s exposure to sunlight to work.

‘If you apply a thin coating of titanium dioxide to a glass surface such as a smarthphone screen, the skin oils and fingerprints gradually disappear from the display by themselves,’ said Dr Michael Vergohl, head of department at the Fraunhofer Institute for Surface Engineering and Thin Films IST in Braunschweig.

The next step is to develop new materials that can also be activated by artificial light.