Photo-Triggered Directional Movement of a Water Droplet on Surfaces by Liquid Crystal Elastomers

The precise control of droplet movement on surfaces remains a major challenge in the field of smart surfaces. Conventional systems based on light, electric, or magnetic stimuli often require the addition of corresponding photothermal, conductive, or magnetic particles into the droplets, which may lead to droplet contamination and hinder encapsulation of drugs or cells for practical application. In the present study, a photo-responsive composite functional surface was designed and prepared. The functional surface contains a liquid crystal elastomer (LCE) layer which is placed underneath a pre-lubricated polydimethylsiloxane surface. Taking advantage of the photo-induced thermal response of the cross-linked LCE network, upon local irradiation with ultraviolet light, the illuminated region of the LCE layer rapidly generates dynamic heating, creating a temperature gradient across the droplet. This gradient alters the surface tension of the solid surface, disrupts the symmetry of contact angles of the droplet, thereby inducing directional droplet movement along the surfaces. The present study provides a non-contact and fast approach for the fabrication of smart surfaces towards more complex droplet manipulation.