Evolution of rim instabilities in the dewetting of slipping thin polymer films

Abstract

Using optical microscopy, we investigated the amplification of instabilities of the moving rim which formed during dewetting of slipping polymer films. At the onset, the wavelength of the rim instability grew in time and proportional to the width of the rim. At later stages, these instabilities led to finger and subsequent droplet formation. Droplet size was found to be proportional to the width of the rim at breakoff of droplets, which, in turn, was proportional to the initial film thickness. Our experiments suggest that the decrease of the dewetting velocity with increasing width of the rim is the key mechanism responsible for this instability. Droplet formation provided a possibility for self adjustment of the dewetting front resulting in a constant mean self- regulated dewetting velocity. This mean velocity was significantly higher than the velocity for the corresponding stable rim.