Session L45: Friction and Brushes

2:30 PM–5:30 PM, Tuesday, February 28, 2012
Room: 159

Sponsoring Unit: DPOLY
Chair: Mark Stoykovich, University of Colorado

Abstract ID: BAPS.2012.MAR.L45.3

Abstract: L45.00003 : The Use of Microscale Geometry to Tailor Stimulus-Responsive Surface Friction

3:18 PM–3:30 PM

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Authors:

  Lin Han
    (Massachusetts Institute of Technology)

  Jie Yin
    (Massachusetts Institute of Technology)

  Lifeng Wang
    (Massachusetts Institute of Technology)

  Khek-Khiang Chia
    (Massachusetts Institute of Technology)

  Robert Cohen
    (Massachusetts Institute of Technology)

  Michael Rubner
    (Massachusetts Institute of Technology)

  Mary Boyce
    (Massachusetts Institute of Technology)

  Christine Ortiz
    (Massachusetts Institute of Technology)

The capability to tailor stimulus-responsive surface friction, including sensitivity profile, range, temporal response and deformation mechanisms, holds great potential for an array of engineering and biomedical applications. In this study, the pH-dependent friction of layer-by-layer assemblies of poly(allylamine hydrochloride) and poly(acrylic acid) (PAH/PAA) were quantified for structures of a continuous planar film and anisotropic microtube forests via lateral force microscopy. By comparing experiments to microstructure-specific finite element modeling, a mechanistic change from surface adhesion-dominated friction ($\mu $=0.11) to viscoelasticity-governed shear (=0.017) was predicted upon ionic crosslink density reduction of PAH/PAA from pH 5.5 to 2.0 for the film (6.5$\times $ decrease). The responsiveness of $\mu $ was further tuned by the tube forest geometry to be 3.5$\times $. At pH 5.5, $\mu $ (=0.094) was lower than the film due to discrete tube bending/buckling and smaller tip-sample interface stress. At pH 2.0, $\mu $ (=0.027) was higher because of inter-tube contact and weaker substrate effect. This study provides an excellent platform to quantitatively access and design dynamic substrates with tailorable stimulus-responsive surface friction.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.L45.3