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A starburst of wrinkles form in a thin film material when a drop of water is placed on the film as it floats in water. These remarkably simple experiments, done with a pool of water in a Petri dish and a low-magnification microscope, give researchers insight into whether the material properties of ultrathin films differ from their properties in bulk quantities.
From:
Jiangshui Huang, Megan Juszkiewicz, Wlm H. de Jeu, Enrique Cerda, Todd Emrick, Narayanan Menon and Thomas P. Russell,
“Capillary wrinkling of floating thin polymer films”, Science, Vol. 317, 650 (2007)
DOI: 10.1126/science.1144616
ABSTRACT: A freely floating polymer film, tens of nanometers in thickness, wrinkles under the capillary force exerted by a drop of water placed on its surface. The wrinkling pattern is characterized by the number and length of the wrinkles. The dependence of the number of wrinkles on the elastic properties of the film and on the capillary force exerted by the drop confirms recent theoretical predictions on the selection of a pattern with a well-defined length scale in the wrinkling instability. We combined scaling relations that were developed for the length of the wrinkles with those for the number of wrinkles to construct a metrology for measuring the elasticity and thickness of ultrathin films that relies on no more than a dish of fluid and a low-magnification microscope. We validated this method on polymer films modified by plasticizer. The relaxation of the wrinkles affords a simple method to study the viscoelastic response of ultrathin films.
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