Surfaces for Liquid Manipulation

Liquids are omnipresent and manipulation of their behavior is important for applications ranging from sanitation to energy production to food production and further. One prominent way to manipulate a liquid is via its interaction with surfaces. By altering the surface chemistry or topography novel behavior is unlocked.

While numerous surfaces have already been developed to manipulate this wetting behavior, many challenges remain unsolved or with great room for improvement due to the complicated liquid-surface interplay. To refine the understanding, water is a convenient model liquid due to its large surface tension.

Generally, water exists either in a continuous or discontinuous form, e.g. as a water film or as water droplets. In this thesis, novel surfaces and methodologies for manipulating water in both forms are developed. They are designed based on existing wetting theory, realized using micro- and nanofabrication as well as simple experimental setups, and characterized using existing as well as developed methods.

Using nanostructured surfaces, water films are created or thickness-confined by eliminating or utilizing the Laplace pressure barrier, respectively. Water droplets are generated by both serial and parallel means. By modifying a consumer-grade inkjet printer, a low-cost tool for precise and versatile droplet production is created.

By critically evaluating existing literature on ‘spatial control of condensation’, supersaturation is identified as a third lever for achieving it. By combining superhydrophobic-hydrophilic substrates with acceleration-mode dip-coating, fast formation of droplet arrays with a gradient in droplet sizes is achieved.

The findings serve as a base from which further development in the field of liquid manipulation can spring. Particularly, attention to both the liquid introduction and the subsequent transition into the desired shape must be paid to be successful.