| Summary: | Investigating the frictional behavior of polydimethylsiloxane (PDMS) with well-controlled roughness in complex fluids is important for biological and chemical applications. In this paper, we adopt an aqueous solution of a charged, hydrophobic acrylate copolymer as a lubricant. The scaling laws between the coefficient of friction (CoF) and the roughness of PDMS, as well as the concentration of the polymer solution in different lubrication regimes, are obtained. In the boundary lubrication regime, surface roughness and lubricant rheological behavior both remarkably influence the CoF. Moreover, the product of the CoF in the boundary regime and the velocity of the boundary-mixed transition is independent of roughness. A full lubricant film forms and shear thinning behavior dominates in the hydrodynamic lubrication regime. Frictional behavior in this tribological system has been successfully regulated. We hope to establish the optimal match of surface roughness and the rheological behavior of lubricant and unveil the mechanism behind the friction phenomenon.
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