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Why pens have rubbery grips

  1. Michael J. Adamsa,1
  1. aSchool of Engineering, University of Birmingham, Birmingham B15 2TT, United Kingdom;
  2. bSorbonne Universités, Université Pierre et Marie Curie Univ Paris 06, Institut des Systèmes Intelligents et de Robotique, F-75005 Paris, France;
  3. cUnilever Research & Development Port Sunlight, Bebington, Wirral CH63 3JW, United Kingdom
  1. Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved August 22, 2017 (received for review April 14, 2017)

  1. Fig. 2.

    Typical evolution of the load force, <mml:math><mml:msub><mml:mi>A</mml:mi><mml:mtext>gross</mml:mtext></mml:msub></mml:math>Agross, and <mml:math><mml:msub><mml:mi>A</mml:mi><mml:mtext>junct</mml:mtext></mml:msub></mml:math>Ajunct as a function of contact time for a glass (red) and for an elastomer (blue) counter surface. The evolution of <mml:math><mml:msub><mml:mi>A</mml:mi><mml:mtext>gross</mml:mtext></mml:msub></mml:math>Agross is independent from the material of the counter surface.

  2. Fig. 3.

    Evolution of the relative junction area <mml:math><mml:mrow><mml:msub><mml:mi>A</mml:mi><mml:mi mathvariant="normal">E</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mrow><mml:msub><mml:mi>A</mml:mi><mml:mtext>junct</mml:mtext></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mi>A</mml:mi><mml:mtext>gross</mml:mtext></mml:msub></mml:mrow></mml:mrow></mml:math>AE=Ajunct/Agross and of the junction density <mml:math><mml:mrow><mml:mi>N</mml:mi><mml:mo>/</mml:mo><mml:msub><mml:mi>A</mml:mi><mml:mtext>gross</mml:mtext></mml:msub></mml:mrow></mml:math>N/Agross as a function of hold time in contact with glass for participants A and B and different loading rates and applied loads. Solid lines show first-order kinetics best fits.

  3. Fig. 4.

    (A) Contrasted kinetics of contact formation for a peak compression of 2 N showing images at the beginning and end of the subsequent hold period. (B) Time course of the evolution of friction for a finger sliding on an elastomeric surface or on a glass surface (fitted to a first-order kinetic relationship) at a velocity of 0.02 m s?1 and under a load of 0.2 N. (C) Pairs of enlarged grayscale images from randomly selected trials with an elastomeric surface.

  4. Fig. S1.

    (A) Schematic diagram of the frustrated total internal reflection technique used to measure the contact area between a finger pad and a glass prism. Light rays are entirely reflected unless there is intimate contact resulting in a dark image against a light background. (B) A 3D grayscale rendering of a fingerprint image.

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