Decoupling parameters of adhesion from viscoelasticity in the human perception of stickiness via shear-stiffening elastomers.

In engineering, the adhesion or "tack" of an object can be related to its bulk material properties and interfacial adhesion, sometimes quantified by a peak adhesive force or work of adhesion. However, it is unknown how these engineering contributions to adhesion compare to the human perception of "stickiness". Here, to decouple between adhesive and viscoelastic parameters, we used shear-stiffening elastomers to modulate viscoelastic and adhesive contributions by velocity. Through psychophysical testing, we discovered that the human perception of "stickiness" is best correlated to a non-canonical parameter, δstickiness, which we call the "stickiness displacement". δstickiness was a better predictor than rheological properties like the loss modulus or tan δ, and better than adhesive parameters like the pull-off force or distance to detachment. Explicitly solving δstickiness in terms of material and geometric properties, we obtained an analytical equation to tune the perceptual "stickiness" of objects which should accelerate the design of tactile interfaces in haptics and assistive devices for low vision, sensory neuroscience, and the "feel" of consumer goods.