By: Pedro Patrício
At: Instituto de Investigação Interdisciplinar, Anfiteatro
When applied to soft materials, such as elastomers, polymeric gels and biological tissues, classical elasticity gives rise to a wide variety of instabilities, yielding beautiful and complex buckling patterns.
In this seminar, we will describe the wrinkling instability produced in long cylindrical elastomeric fibres, of radius in the tens of nanometres to tens of microns range. Each fibre consists of a soft core and a stiff outer half-shell, which are length-mismatched because of differential solvent de-swelling. Unexpectedly, the fibres only wrinkle after attaining a well-defined helical shape. We propose a simple analytical model, which allows the curvature and wrinkle wavelength to be determined, as well as the transition between the âcurlingâ and âwrinklingâ regimes.
This new type of instability may also be found in the tendrils of climbing plants as they dry and lignify. Just as plant tendrils are curled when young, but asymmetrically wrinkled when aged, so are our micro- and nano-fibres. This behaviour on two vastly different length scales can be described by the same elastic model.