Printed materials inspired by nature

Superhydrophobic materials are found in many forms in nature, from scales on shark skin that reduce drag to lotus leaves whose surface enables water to roll off and remove dirt particles in the process. The way in which water interacts with these surfaces in nature is inspiring the work of a team of researchers from Carnegie Mellon University.

A study published in Advanced Materials Technologies illustrates a new method for creating superhydrophobic surfaces using an aerosol jet printer and polymer solutions. The findings illustrate a technique through which polymer microgel particles are deposited onto a substrate in a specific pattern. This new method is unique in that it offers precise control over the shape and location of the structures, while requiring no post processing.

“The polymer we used is slightly hydrophobic and is widely utilized in wearables due to its durability and flexibility,” said Mohammad Islam, a professor of materials science and engineering who contributed to the research. “The superhydrophobicity of the surface can be attributed to its unique surface characteristics.”

Aerosol jet printing is an advanced additive manufacturing technique used to create precise components and structures by converting a liquid ink containing functional materials (i.e. metals, polymers, or ceramics) into a fine mist of tiny droplets that are carried by a gas to form an aerosol. A focused stream of aerosol is then deposited onto a substrate through a nozzle where the ink droplets exit and adhere to the substrate.

This process allows for high precision and versatility while using a variety of material types. In this study, three different solvents with varying vapor pressures were used. During the droplets' transition from the printer nozzle to the substrate, the droplets transformed into microgel particles that created a rough, superhydrophobic surface. 

“Usually aerosol jet printing results in droplets coalescing on the surface and then drying to form a thin film,” said co-author Gary Fedder, a professor of electrical and computer engineering and director of the Manufacturing Future Institute. “However, we found that jetting with a solvent having a high vapor pressure resulted in deposition of gelled spheres when they hit the surface, sort of like micro-sized hail. The gelated spheres form the micron-sized surface texture while the printing enables fine patterning.”

We found that jetting with a solvent having a high vapor pressure resulted in deposition of gelled spheres when they hit the surface, like micro-sized hail.

Gary Fedder, Faculty Director, Manufacturing Futures Institute

Existing methods of achieving superhydrophobicity face challenges in regard to manipulating materials properties, as well as complexity and time investment. This method provides a less time-consuming, more controllable way to create superhydrophobic surfaces by manipulating the solvent evaporation rate and polymer gelation process during deposition.

As superhydrophobic materials offer numerous benefits across various industries, this discovery has potential for a wide range of applications. The materials could be effective in separating oil from water, which is useful in environmental cleanup and industrial processes. Retardation of droplet evaporation could result in improved efficiency in cooling systems and improvements in water conservation. Droplet manipulation could also improve energy efficiency by enhancing heat transfer in cooling systems.

Additional contributors to this research include Ke Zhong (CMU Materials Science and Engineering), Jace Rozsa (CMU Electrical and Computer Engineering), Dinesh K. Patel (CMU Mechanical Engineering), and Lining Yao (University of California, Berkeley, Mechanical Engineering). Read more about the MFI project.