Sticky Crumpled Matter

 

A sheet which is increasingly confined is forced to bend more and more in order to fit in to the confining volume.  The result is surprisingly stiff, making a crumpled sheet a good packing material, but it is still unclear how to predict exactly how much compression a given crumple can hold.  In this work we discuss how surface/surface interactions (adhesion) affect the compressive strength of a model crumpled polymer sheet.  We combine both experiments and coarse-grained molecular dynamics simulations and make three key observations: 1.) crumples increase in compressive strength when adhesion is present.  Surprisingly, the increase is not proportional to the strength of adhesion.  2.) the work done during a compression cycle, however, does depend on the strength of adhesion.  3.) a new lengthscale is required to predict when a sheet is ‘sticky’ or when it is not ‘sticky’.