Department of Polymer Science and Engineering, University of
Massachusetts, 120 Governors Drive, Amherst, MA 01003 USA
Thin sheets are much more easily bent than stretched by
external forces. One might imagine that it is possible to achieve
a purely stretched state of a sheet by applying a tension in the
plane of the sheet. However, even a sheet subject to purely
planar tension will often choose to deform out of plane to form
wrinkles. This is an everyday phenomenon that can be seen on our
skin as it is stretched by smiling, scars In this work, we report
on a study of wrinkling of films under capillary forces, which
has thus far remained relatively unexplored. Since thin films are
often immersed in fluid environments, both in biological and in
synthetic soft materials, the elastic deformation of films under
surface tension is a relatively commonplace situation. Thin
polymer films form an ideal experimental setting in which to
explore wrinkling phenomena: we study films with very high aspect
ratios (the ratio of lateral size, D, to thickness h is D/h ~
5x105) which can be treated accurately in the framework of
2-dimensional elasticity. Our results demonstrate that wrinkling
can be used as the basis for a metrology of both the elastic
modulus and the thickness of ultrathin films using a very
elementary apparatus - no more than a low-magnification
microscope and a dish of fluid. Finally, we show that wrinkling
patterns can also be used to characterize dynamical relaxation in
ultrathin films.
Research done in collaboration with J. Huang, N.
Menon, Physics Department, University of Massachusetts Amherst,
W. de Jeu, Polymer Ecience and Engineering Department, University
of Massachusetts Amherst, E. Cerda, Physics Department,
Universidad Santiago, Chile
