(42j) Effect of Slug-Trail Mimicking Solution on Silanized-Silicon Tribology

Drops retention force experiments using the Centrifugal Adhesion Balance (CAB) showed that for most liquid-surface systems, liquid drops placed on surfaces are set in motion due to a force that increases with the drops resting time, t_rest, until it reaches a plateau. The force increase was attributed to deformation and molecular re-orientation of the substrate surface. Surprisingly, Water-Graphene system was established to be an exception to the above-mentioned observations owing to the system peculiar tribological behavior. The lateral force, , required to slide a water drop on a graphene surface, is practically constant with t_rest, while the drop’s three-phase contact line shows a peculiar micrometric serrated form. The stiffness and chemical homogeneity of the graphene substrate were responsible for the substrate molecular re-orientation inexistence and hence the tribological uniqueness of graphene surfaces. Here, using the same experimental set up (CAB) for drop retention force measurements we establish that the lateral force, , required to slide a gel drop on a graphene surface, and a gel drop on silanized silicon surface, decreases and increases with t_rest respectively.

These counterintuitive results are attributed to polymer adsorption from the gel drop to the graphene and silanized silicon surfaces, thereby changing the chemical nature and effective stiffness of the substrate right underneath the gel drop. The prepared gel solutions used as the liquid drops in these experiments are thought to mimic lubrication similar to that left behind on slugs trail. Based on the gel-graphene force measurement results, which exhibited unprecedented graphene lubricity through the decrease of with t_rest, the gel solutions could be used as special lubricants. However, the same gel solution used with silanized silicon surfaces unveils an increase of with t_rest.