Spontaneous formation of double helical structure due to interfacial adhesion

Many quasi-one-dimensional micro/nanomaterials assume double or multi-stranded helical conformations, but the reasons are still unclear. On the basis of continuum mechanics analysis, we demonstrate that interfacial adhesion is a significant physical mechanism responsible for the formation of some double helices, especially at micro and nano scales and for soft materials. With the formation of a double helical structure by two nanowires, surface energy decreases while elastic strain energy increases. Their competition dictates the global morphology of adhered micro/nanowires or tubes. The theoretical model agrees well with relevant experiments.