How do we recognize water and oil through our tactile sense?

We can distinguish water and oil through our sense of feel, because the frictional properties of a water film are characteristic. However, we found that it was difficult to distinguish water and silicone oil on a glass substrate only by its feel. Friction evaluation showed that we recognize the liquid as water when the frictional resistance is large and changeable. On a glass substrate, water and silicone oil were not distinguishable, since both had a large frictional resistance. Statistical analysis suggested the contribution of the wettability of solid substrates to their tactile feel. This finding shows that we distinguish water from oil based on the significant friction properties; it is applicable to virtual reality systems, as well as cosmetics, food, and textiles.