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Can we make glass more tactile?

How small are the differences that the human finger can feel? Is it possible to alter the surface chemistry of glass to provide a more pleasurable sensation, for example when using your mobile telephone? The answer is yes, and the key to user-friendliness is friction.

Our sense of touch allows us to perceive a surface in a number of ways ; for example, if it is hot, cold, smooth, rough, pleasant to the touch or disagreeable. Can various surface be differentiated simply by altering the surface chemistry? RISE asked these questions together with Swiss glassmakers Glas Trösch.

“We wanted to study whether a human finger can differentiate a smooth surface simply from a variance in chemical composition, as well try to understand which physical properties affect whether a surface is perceived as pleasant or not,” says Aneliia Wäckerlin, project manager in R&D Coatings at Glas Trösch.

Is perception measurable?

RISE and Glas Trösch shared an interest in being able to quantify sensation – to be able to use scientific methods to measure the experience of a thing, in this case the emotional experience of touching glass. Earlier projects have focused on structured surfaces, in order to study the smallest structures the finger can distinguish. All structure was now removed, with only variations in surface chemistry remaining.

"We have previously demonstrated that surface structure is an effective method for altering emotional experience. We now see that the experience can also be altered by varying the surface chemistry,” says Lisa Skedung, senior researcher in perception delivery at RISE.

Research subjects asked to judge

First and foremost, the desire was to discover whether it was even possible to feel variations in the different surfaces and, if so, which surfaces were most pleasing to the touch.

Research subjects taking part in the study were asked to feel two glass surfaces at a time, each with a thin film of various types of molecules. The subjects where then asked to put a figure on the similarity in how they perceived the surfaces. They were also asked to rank the films from least to most tactile. By analysing the perceived variations, it was possible to prepare a perceptual map.

"When setting out to produce new materials, this map can be referenced to see which physical properties common to the surfaces that people like the most. Can we make even greater use of this to develop something that people like even more?” asks Lisa Skedung.

When it comes to surfaces on objects such as telephones or tablets, a great deal of work goes into how the surface feels, and there is a real desire to be able to control how the surface is perceived.

Some surfaces more pleasant than others

So, which glass surfaces do we find most tactile? The study showed that we prefer low-friction surfaces. As anyone who has tried to draw their finger across a glass surface will have noted, glass has a relatively high-friction surface,” says Lisa Skedung.

“Although it is smooth, the friction is very high. Certain of the films we tested on glass surfaces did reduce the friction slightly and it was these that people preferred. Armed with this insight, we can move on and ask ourselves: can we control the properties of glass so that friction is reduced even further, thus making the glass even more tactile?” wonders Lisa Skedung,

Knowledge gained in the project can be applied to predict the emotional experience and improve the design of surfaces whose tactility is crucial to whether or not a consumer will buy a product, a form of tactile design of interiors and electronic goods.

“The results demonstrate that people are able to differentiate smooth surfaces with their fingertips not only based on the different groups of surface film – nonorganic, hybrid, organic – but also based on different chemical functional groups. Although friction did turn out to be important, it appears that a complex interaction is at work between friction and at least one other surface property that we need to understand better,” says Aneliia Wäckerlin.

Tomorrow’s tactile materials

RISE has been working for a number of years to build up an organisation around how we can link the experience of perception as measured by studying research subjects with instrumental measurement data, a field known as psychophysics. This is so that we can understand which properties are important to various experiences of materials and surfaces so that, in future, we will be able to develop new materials or products that deliver a specific sensation.

“We have seen an enormous interest from industry in being able to predict the perceptual experience of a product based on instrumental measurements, which are less time-consuming and more cost-effective that measuring on humans,” says Lisa Skedung.