Microchannel Induced Surface Bulging of a Soft Elastomeric Layer

Abstract

When a wetting liquid fills in microchannels embedded inside a thin elastomeric layer, the surface of the layer does not remain smooth but bulges out in the vicinity of the channels. The height of the bulge depends on the deformability of the layer and the surface tension of liquid; in addition, it depends also on the vertical location of the channel from the surface of the layer and the channel diameter. While, for liquids of low viscosity ∼500 cP bulging occurs instantaneously, for liquids of high viscosity ∼4000 cP, it occurs over a period of time. Concomitant to bulging of the layer, the cross section of the channel alters too in its shape and size suggesting that the elastic energy penalty associated with the bulging of the layer is supplied by the interfacial energy of the liquid–air and liquid–solid interfaces. Local bulging of the layer alters also its local deformability which is demonstrated by contact mechanics experiments: indentation with a spherical indenter yields a non-circular contact area, the shape and size of which vary with the depth of indentation. Thus, sub-surface microchannels can be suitably used for generating surface patterns on the elastomer and also for modulating its modulus.