Superhydrophobic Copper Foils Via Aqueous Ammonia Etching and Alkyltrichlorosilane Modification

Using surface modification to generate unique properties on a variety of substrates has been a field of intense investigation in recent decades. One poster-child of this work has been the development of countless methods for achieving superhydrophobicity – that is, liquid contact angles in excess of 150° - on myriad substrates. However, this development has lagged for certain materials, such as engineering metals (copper, aluminum, etc.) and inorganic metal oxides, due to technical challenges associated with their high surface energies. In this work, a simple immersion method is presented as a route to superhydrophobicity on copper foils. The foil is cleaned ultrasonically and then etched in aqueous ammonia for 24-72 hours, allowing for evaporation of the etchant. Initially, oxygen adsorption corrosion drives the dissolution of copper. After some time, a copper hydroxide precipitate forms and slowly deposits as a patina layer on the copper surface. When evaporation is complete, the copper hydroxide coated foil is exposed to an alkyltrichlorosilane, and subsequently, water contact angles as high as 165º may be observed.