Reducing Friction in Sliding Contacts with Skin Equivalent Silicone Rubber by Polymer Coatings in the Presence of water or Silicone Oil

The friction and lubrication of skin plays a major role in product development for cosmetics, textiles, artificial turf and medical devices. Yet, few tools are available to actually influence friction in skin product interactions, in a deterministic way. A promising direction could be the development of polymer coatings in combination the concept of hydration lubrication [1][2]. Experimental work was done using a polymer coated glass plates and skin substitute silicon skin L7350. This mechanical skin equivalent is used by FIFA for determination of skin-surface friction in combination with artificial grass. Friction experiments at boundary lubrication conditions showed values for the coefficient of friction lower than 0.01 in case of hydrated PAA-g-PEG coatings, measured for a sliding contact with a flat-on-flat configuration. The effect of binding dodecane and silicone oil to polymeric coating structures based on PAA, PEG, PE or PDMS was measured and compared with the results obtained in an aqueous environment. The results show combinations for which the coefficient of friction was reduced from f ? 1-2 at dry conditions to below f = 0.1 a sliding velocity of 10 mm/s.
Friction was reduced most in the presence of water, yet silicone oil could serve as alternative. Results with a pin-on-plate setup and coatings based on polysorbitol and polyglyceryl confirm the excellent friction reducing properties of hydrophilic polymer coatings that can bind water to the surface. The polymerization degree of polysorbitol and polyglyceryl is a critical parameter for the lifetime of the polymer coatings in an aqueous environment.