Why do some touchscreen gadgets look clearer than most, and why do others attract fingerprints?

Until now, no one really knew. But today, scientists at the 238th National Meeting of the American Chemical Society described the development of a test to assess the performance of smudge- and reflection-resistant coatings on touchscreen displays.

It might sounds like a trivial issue but phone, camera and media player manufacturers spend millions to ensure that their touchscreens are easy to view in bright light and resist greasy finger smudges.

Screen test

However, the structure and mechanisms of screen coatings are poorly understood, so Dr Steven Carlo developed a test to determine the chemical composition and effectiveness of smudge and reflective resistant materials. Carlo explains, "Surfaces are particularly important in consumer products. Our work investigates how products can be modified to reduce smudging and reflections. These modifications can offer improved resistance to fingerprints, anti-reflection properties or enhanced physical resistance."

The basis of anti-smudge coatings is a perfluoro alkyl ether, a derivative of Teflon with added chemicals to enhance its repellent effects. Anti-reflective materials use alternating layers silica and aluminum to bend and diffuse light to reduce glare.

Carlo and his team used depth profile X-ray photoelectron spectroscopy to compare the chemistry of these coatings. Anti-reflective coatings need alternating layers, which have differences in their refractive index, a measure of how fast light travels through a material. Fluorocarbons in general have low refractive indices and offer anti-smudge properties.

XPS allowed the scientists to visualize the multi-layer structure and the chemical species present in each layer. In general, they found that the greater the number of layers there are in a coating, the greater the anti-reflective properties. Carlo and his team also discovered that more silica and aluminum layers led to better glare reduction.

The tests should lead to tougher, crisper screens - and may even mean that future touchphones don't require ugly protective skins.