 Hello, I'm Xinyi from Texas A.M. University. The sense of touch has been found to affect people's preference towards different consumer products. For example, when you are doing a grocery shopping, a well-designed packaging of an organic pasta may have a higher quality feeling than other regular pastas. However, this conventional trial and error process is not enough to find the optimized design. Then the question arises, can we predict how textures services feel before fabrication? Let's see one example in the food packaging industry. People have been using micro-particle coatings to reduce the friction force for a better feeling. Here are two plastic films from DAO. One was coated with larger and softer particles and the other was coated with smaller but safer particles. We found that the dry contact area of the large particle sample is higher than small particle sample through the finite element contact modeling, which means that the small particle sample should have a lower friction force and is the option. However, it's not always the case. We measured the friction forces between the finger and two samples for different finger conditions. For the clean finger, the large particle sample has a higher friction as the dry contact area simulation predicts. But for the natural finger, the small particle sample has a higher friction. This indicates that the dry contact area can represent the real friction and the multi-physics arising from sweat and lipids must be considered for the predictive design. Let's now zoom in to one aspect and see what mechanisms are involved at micro-scale. At the finger material interface, because of sweat, capillary bridges form between the particles and skin surface. Considering the natural finger, it's usually covered with the lipid film, which increases the skin surface energy and decrease the contact angle and increase the capillary force. Then we simulated the contact area considering capillary. First, the particle is deformed by the normal load applied from the finger. Then the capillary bridge profile is simulated and it pulls the two surfaces into more contact. Here's the simulation results with four different cases. For the clean skin, the small particle sample has a lower friction force as the dry contact area simulation results because of small capillary forces. However, for the natural skin, the small particle has much higher capillary force, which makes it to have a larger contact area, thus a higher friction force than the large particle sample. For the large particle sample, we do see a small increase in the contact area, but it's very likely that interfacial shear strength is reduced with thicker lipid film. This effect is more dominant, so there is a decrease in the friction force. Thank you all for listening.