Suyash Gairola

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

While holding any object, there is an active interaction between our fingertips and the object’s surface. Both the normal and the frictional load applied by the human fingers play an essential role in this tactile exploration. The system under study can be generalized, and the study’s goal is to investigate friction between a deformable patterned soft substrate (Elastic modulus ≈1MPa) and a stiffer substrate in the presence of boundary lubrication. Coefficient of friction (COF) values were calculated using the human finger for different lubricating solutions and different substrates. All the measurements were made on an in-house developed strain gauge-based force sensor, capable of measuring both the normal and the frictional force simultaneously and independently. The results indicate that adding a small quantity of lubricating solution between the finger and the substrate drastically reduces friction. Surfactant solutions like Sodium dodecyl sulphate (SDS) facilitates boundary lubrication and gives COF values of about 0.2 for high bulk concentrations. The COF between the finger and the glass substrate varies with changing the bulk concentration of the surfactant. The adsorption of the surfactant onto the surface is responsible for a decaying nature of the COF vs time profile.