Flexible pressure-sensor film shows how much force a surface 'feels' -- in color

Yadong Yin and colleagues explain that pressure is a part of our daily lives. We and the objects around us constantly exert pressure on surfaces, from a simple, light touch of a finger on a smartphone screen to the impact of a head-on car collision. To design better cars, smartphones and other objects we use every day, scientists need to know how much force they can withstand. Most pressure gauges are bulky hunks of metal that can't fit into tight spaces. Other sensors on the market are thin and can indicate stresses with different shades of the same color, but they are difficult to interpret and have low resolution and contrast, says Yin. To overcome these challenges, the team turned to nanoparticles -- which are so small that 1,000 would fit across the width of a human hair.

Tiny gold nanoparticles can join together in chains, and disrupting these chains results in a change in color. The researchers took advantage of that unique property to design a new type of pressure-sensor film, which is a deep blue color when the nanoparticles are linked together, but becomes ruby red when the nanoparticles irreversibly disassemble under stress. "Our colorimetric sensor film changes color, not just color intensity, which gives us the benefit of higher contrast and resolution," says Yin. "We also can make it into a liquid, which can be painted on objects such as crash test dummies that have complex surfaces."