Suyash Gairola

Tactile friction under boundary lubrication: Surfactants and their propensity to reduce fingertip friction using surfactant

Tactile exploration involves dynamic interactions between fingertips and object surfaces, governed by both normal and frictional forces. To understand these interactions, the friction between a patterned, deformable soft substrate and a rigid substrate under boundary lubrication by human fingers was Investigated. This study has potential applications in areas like tactile sensing, haptic devices, prosthetics and design of textiles and FMCG goods. Using a custom-built strain gauge sensor, both normal and frictional forces were measured simultaneously and independently for various lubricating solutions applied to the fingertip interacting with a glass substrate. The results demonstrate a significant reduction in friction upan introducing a surfactant acting as a lubricant as compared to dry contact. Solutions containing surfactants, like Sodium Dodecyl Sulfate (SDS), exhibit efficient boundary lubrication, achieving Coefficient of Friction (COF) values as low as 0.2 at high concentrations. Notably, COF exhibits an asymptotic behavior beyond the surfactant’s critical micellar concentration, suggesting saturation of the interface. Further, the COF-time profile changes its nature as the bulk concentration increases and experiments indicate that the adsorption of surfactant molecules onto the surfaces is the cause for this.