Creasing-wrinkling transition in elastomer films under electric fields

Abstract

Creasing and wrinkling are different types of instabilities on material surfaces characterized by localized singular folds and continuously smooth undulation, respectively. While it is known that electric fields can induce both types of instabilities in elastomer films bonded on substrates, the relation and transition between the field-induced instabilities have not been analyzed or understood. We show that the surface energy, modulus, and thickness of the elastomer determine the types, critical fields, and wavelengths of the instabilities. By independently varying these parameters of elastomers under electric fields, our experiments demonstrate transitions between creases with short wavelengths and wrinkles with long wavelengths. We further develop a unified theoretical model that accounts for both creasing and wrinkling instabilities induced by electric fields and predicts their transitions. The experimental data agree well with the theoretical model.

Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning

“…We further define the uniform electric field in flat regions of the EMCR film as the applied electric field E. The three terms in equation (2) denote the electrostatic potential energy, the strain energy of the EMCR film and the buffer substrate, respectively. The surface energy has negligible effect in the current study 38,48 . The electrically induced pattern formation is driven by the decrease of electrostatic potential energy and resisted by the increase of strain energy.…”

“…Similarly, by dimensional argument, the wavelength of the wrinkle at the onset can be expressed as 48 …”

Elastocapillarity: Surface Tension and the Mechanics of Soft Solids

“…(b) Soft silicone layers of varying thickness are swollen by applying an electric field across them. As the ratio Υ/HE varies, there is a dramatic shift in the form of the surface instability [41]. c) Cylinders of soft agar gels are released in toluene and allowed to relax.…”

On-demand hierarchical patterning with electric fields

“…Thereafter, when the applied electric field in the bottom elastomer film is increased to a critical value E 2c % 1:03 ffiffiffiffiffiffiffiffiffiffiffi l 2 =e 2 p , a second-order pattern of creases form in the bottom film with the top thin film acting as a skin layer. While it is known that the skin layer or surface energy can affect the critical electric field for creasing instability, 20,27 the effect of the skin layer has been observed to be negligible in the current study. Furthermore, following Eq.…”

“…19 The critical electric field for inducing electro-creasing instability in a layer of an elastomer scales with square root of the elastomer's modulus, while the wavelength of the instability pattern scales with the layer's thickness. [19][20][21][22][23][24][25] By rationally designing multiplayer elastomer films with varied modulus and thickness throughout different layers, we can control the formation of instability patterns with feature sizes of different length scales under prescribed voltages.…”