Mechanical Model of Globular Transition in Polymers

In complex, multicomponent systems, polymers often undergo phase transitions between distinct conformations. This paper reports a millimeter-scale granular model of coil-to-globule transitions: one “polymer” chain—a cylinders-on-a-string “pearl necklace”—and many spheres, all shaken on a horizontal surface. It is possible to describe the behavior of this granular system by using formalisms generally used in statistical physics of polymers. Two sets of experiments allowed the observation of firstand second-order coil-to-globule transitions. The model shows that the competition between longand shortrange interactions leads to a first-order transition. Well-designed granular system represents another kind of approach to the study of polymer phase transitions and might inspire future designs of polymer-like mesoscale systems.