Rational design of ionic-liquid infused porous surfaces as liquid repellent coatings

• Applicant: Professor Dr. Nicolas Vogel
• Subject Area: Mechanical Process Engineering
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 396492435

The uncontrolled adhesion of contaminants onto surfaces can drastically decrease the performance of a material in a wide range of technological applications, ranging from clogging in filtration and membrane technology to vision loss in optical devices or pathogen contamination in the healthcare sector. The design of repellent, non-fouling surface coatings is therefore a key engineering challenge.Potential solutions to this problem have evolved from inspiration by the natural world. The traditional role model for the design of repellent surfaces is the Lotus plant, which imparts superhydrophobic properties but can fail to repel low surface tension liquids or complex fluids.An alternative solution is inspired by the Pitcher plant and employs a fluid lubricant layer that is infiltrated into a porous surface coating. This lubricant infiltration prevents direct contact of the surface with a second, contaminated liquid, leading to efficient repellency as the liquid slides off the lubricant layer. Such coatings have shown remarkable repellency of water, low surface tension liquids and complex fluids and great potential for the prevention of fouling by bacteria adsorption, the reduction of ice adhesion, and self-healing characteristics as the fluid lubricant can flow back into damaged parts of the surface. However, the lubricant layer can evaporate, thus degrading the coating over time and at elevated temperatures. Here, we aim to mitigate failure by loss of lubricant using ionic liquids with extremely low vapor pressure as the lubricant. To this end, we will first focus on a detailed, molecular understanding and optimization of the interactions of ionic liquids with the surface. We will use silane chemistry to introduce chemical functionalities onto glass model surfaces and measure the interfacial energy with the ionic liquid. We anticipate that mixed self-assembled monolayers with multiple functional moieties may be required to minimize the interfacial energy, as a consequence of the chemical heterogeneity of ionic liquids. A low interfacial energy is a requirement to create a stable solid-lubricant interface that is not replaced by the liquid to be repelled. Second, we will create highly ordered nanoporous surfaces (inverse opals) as model coatings to investigate the wetting behavior with ionic liquids. We will use the change in structural color upon infiltration and replacement with a second liquid to visualize the repellency properties as a function of the applied surface chemistry. We will then transfer the concept to a simple and scalable coating process. Finally, we will optimize the long-term repellency properties by changing the silane monolayers to surface-bound thin films of active ester-based polymer networks. These can be quantitatively replaced by functional amines, providing side groups that mimic the structural elements of the ionic liquids and thus maximize the chemical affinity with the lubricant.

• DFG Programme: Research Grants