Abstract
Controlling and predicting friction is a significant scientific and technological issue. It is our everyday experience that two smooth surfaces slide more easily over each other than two rough ones, due to interlocking of the rough surfaces. However, the interpretation of such friction forces is difficult since other contributions arise from e.g. adhesion forces, that are harder to control. Here, we demonstrate that designer macroscopic roughness can be used to control, dynamically tune and quantitatively predict friction. We show that the roughness allows to tune the friction coefficient by more than an order of magnitude, which can be explained completely by a simple Coulombic friction model. A kirigami metamaterial surface with externally tunable roughness allows us to show that this understanding of geometrical friction can be used to control on-the-fly the friction in a single system by dynamically controlling its roughness.
Highlights
The major goal of tribology is to reduce friction and wear to increase energy efficiency [1]
We study the effect of interface geometry separately by macroscopic patterning, allowing to control and predict the friction that results from the interface geometry and separate it from the adhesion contributions
The roughness can be purposely changed to tune the magnitude of the friction force variations and its average
Summary
The major goal of tribology is to reduce friction and wear to increase energy efficiency [1]. When rough surfaces slide over each other, the roughnesses will interlock, deform and oppose the motion and generate friction [5,6,7,8,9]. The competing effects of friction generated by roughness slopes that (almost) interlock and adhesion are notoriously difficult to disentangle, since the surface roughness typically spans all length scales from atomic to macroscopic [12,13,14]. We show here that by controlling the interface geometry, we can dynamically tune friction externally, without changing the slider. We achieve this by using kirigami metamaterial surfaces. Our work provides vistas for the use of geometry and metamaterials for the control of friction
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