Sliding-induced adhesion of stiff polymer microfibre arrays. II. Microscale behaviour

Bryan Schubert, Jongho Lee, Carmel Majidi, Ronald S Fearing

Abstract

The adhesive pads of geckos provide control of normal adhesive force by controlling the applied shear force. This frictional adhesion effect is one of the key principles used for rapid detachment in animals running up vertical surfaces. We developed polypropylene microfibre arrays composed of vertical, 0.3 μm radius fibres with elastic modulus of 1 GPa which show this effect for the first time using a stiff polymer. In the absence of shear forces, these fibres show minimal normal adhesion. However, sliding parallel to the substrate with a spherical probe produces a frictional adhesion effect which is not seen in the flat control. A cantilever model for the fibres and the spherical probe indicates a strong dependence on the initial fibre angle. A novel feature of the microfibre arrays is that adhesion improves with use. Repeated shearing of fibres temporarily increases maximum shear and pull-off forces.

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Footnotes

  • The Tabor parameter (Johnson 1997) is approximately 1.6 which suggests the contact is within the DMT–JKR transition region, but it is closer to the JKR region. The difference between the DMT–JKR transition region and JKR is slight enough that we will assume JKR for simplicity.

    • Received November 18, 2007.
    • Accepted January 2, 2008.
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