Tunable stimulus-responsive friction mechanisms of polyelectrolyte films and tube forests

The pH-responsive frictional behavior of layer-by-layer assembled poly(allylamine hydrochloride) and poly(acrylic acid) multilayers is quantified in different geometric forms of a continuous planar film and anisotropic tube forests. A mechanistic change from surface adhesion dominated frictional behavior to visco/poroelasticity-governed shear occurs for the planar film upon pH-stimulus. This pH-dependent friction can be further controlled by the discrete anisotropic geometry of the tube forest, which introduces additional friction due to asymmetric deformation of the discrete bending of the tubes during lateral motion. This study provides important insights into the design of polyelectrolyte-based coatings with a wide range of controllable surface frictional properties, tuned via interactions between the inherent stimulus-responsive material behavior and the microgeometry of the anisotropic tube forest.