Mechanisms of reversible stretchability of thin metal films on elastomeric substrates

Abstract

Gold films on an elastomeric substrate can be stretched and relaxed reversibly by tens of percent. The films initially form in two different structures, one continuous and the other containing tribranched microcracks. We have identified the mechanism of elastic stretchability in the films with microcracks. The metal, which is much stiffer than the elastomer, forms a percolating network. To accommodate the large elongation of the elastomeric substrate, the metal network twists and deflects out of the plane but remains bonded to the soft substrate. Consequently, the metal film experiences only small strains and deforms elastically without suffering fatigue.

Microstructured Silicone Substrate for Printable and Stretchable Metallic Films

“…Ideally, a stretchable conductor should have a high electrical conductivity, be easily patterned onto the elastomer surface, and be robust to large mechanical stretch. Elastic wiring can be prepared by patterning thin or thick metal films on the silicone membrane 1,4,5,9,10 or by preparing conducting composite silicones. 3 The former have high electrical conductivity (>10 6 S/m) but require complex patterning processes; the latter are extremely robust to mechanical stretching but have low conductivity (∼1000 S/m) and are not readily compatible with microfabrication techniques.…”

Engineering reversible elasticity in ductile and brittle thin films supported by a plastic foil

“…The engineered substrate may then contain patterned thin film devices, which could be encapsulated in stretchable silicones. We hypothesize that when reducing the size of our Y-shape cuts, the out-of-plane deflection will be small and not hindered by the encapsulation material, similarly to the microcracked gold films, which are stretchable even when fully encapsulated in PDMS [2,13]. This approach will have applications in a wide range of flexible and stretchable devices.…”

“…The later usually have three ''branches'' (forming Yshaped motifs) and are randomly distributed over the film surface area. Upon stretching, minute deformation occurs in the thin gold ligaments as they deflect out-of-the-plane, thereby preserving the electrical conductivity of the metal film [13].…”

Elastically Stretchable Insulation and Bilevel Metallization and Its Application in a Stretchable RLC Circuit

“…The cracks allow the film to elongate by twisting out of plane, so that even at large elongation, only a small, elastic strain is induced in the film. 11 While microcracks enable the conductors to stretch elastically, they also cause the measured resistance of the conductors to be higher than the resistance 10 calculated from the resistivity, q, of bulk gold:…”

“…11 Microcracked gold conductors have several advantages, a major one being that microcracked films can be stretched isotropically, whereas both meander-shaped and wavy gold conductors can only be stretched anisotropically. Also, the deposition and patterning of microcracked gold films can be accomplished with standard microfabrication technology without requiring mechanical prestrain 9 or electrodeposition of a thick gold film.…”