Effects of distribution of microconcave array with nanofolds on the water adhesive property of PDMS films

PDMS films with microscaled concave array and nanofolds were prepared by a cas-ting technique using the front rose petal surfaces as the template. The distribution of the PDMS film's microstructures was changed by stretching the film all-directionally. The morphology of the PDMS films was observed by field emission scanning electron microscope(SEM) and atomic force microscope(AFM) at different stretch stages. The water adhesive effect was characterized by the high-sensitivity microelectromechanical balance system, and the effect of micro- and nano-structure on the water adhesive property of the PDMS film was investigated by altering the stretch stage. The wettability was characterized by the apparent contact angle. The experimental results show that the distribution density and the depth of the microconcave decreased through stretching, and the adjacent microconcaves separated from each other gradually. The water droplet could immerse into the microconcaves much more easily, and the adhesive force between the water droplet and the film increased immediately. Besides, the nanofolds in the bottom of the microcaves would be stretched with the stretch of the film. With the stretch of the nanofolds, more air could be trapped and the adhesive force would decrease. If the water droplet could immerse into the nanofolds, the adhesive force would increase again. After the complete immersion of the water droplet into the nanofolds, the adhesive force would decrease resulted from the solid-liquid contact area reduction. Therefore, the high adhesive force is mainly caused by the micro- and nano-scaled structure.