Bubble Dynamics at Functionalized Surfaces

Motivation

Bubble dynamics at solid surfaces is essential for different industrial processes, e.g. electrolysis or flotation. Surface functionalization provides an elegant means to control the bubble dynamics in existing geometries, or to combine it with novel reactor geometries and internals for maximum flexibility and effectivity.

In order to increase the efficiency of proton exchange membrane (PEM) electrolysis, both more intensive cooling and optimization of the bubble dynamics and gas-liquid separation are required. One approach is to specifically influence oxygen bubble formation in the anode circuit through interaction with functionalized surfaces. An improved oxygen separation in the gas-liquid separator, for example, has the potential to reduce the overvoltage and increase the heat transfer when cooling the process water.

Goals

• Apply stable surface functionalization layers on different substrates and surface structures for an enhanced or hindered bubble nucleation process
• Analyze the impact of surface structure and chemistry on bubble formation and unravel the underlying mechanisms
• Effect of surface functionalization on bubble nucleation, growth, coalescence and detachment

Techniques

• Surface chemistry modification via Plasma-Enhanced Chemical Vapour Deposition (PECVD) or surfactant adsorption
• Surface structure modification via additive manufacturing or laser structuring
• Contact angle measurement
• Streaming potential and X-ray photoelectron spectroscopy (XPS) to characterize surface chemistry
• Bubble nucleation setups with optical microscopy, in quiescent supersaturated solutions or under defined flow conditions
• Controlled liquid supersaturation and oxygen content measurement

Results

It was possible to generate structures and coatings with a water contact angle ranging from 20° up to nearly superhydrophobic conditions. XPS revealed different aging mechanisms like the introduction or reorientation of polar surface groups or defluorination. The results indicate that the surface character of the substrate adapts depending on the surrounding media and needs more time to reach a steady state for deeper structures. It is shown that a higher hydrophobicity of the structured surface yields a stronger interaction with the dissolved gas. This significantly enhances the oxygen nucleation up to nearly 1000%. However, this effect is combined with smaller bubble sizes and a reduced detachment rate, and impacts the bubble coalescence dynamics on some substrate structures. The attachment of rising oxygen bubbles to surfaces and the bubble transport in open-pore foams can also be significantly influenced by a surface coating.

Publications

Heinrich, J., Schwarzenberger, K., Marquardt, T., Yang, X., Marzec, M., Manthey, J., ... & Eckert, K. (2025). Surface Functionalization of Additively Manufactured Materials by PECVD and its Influence on Wettability and Oxygen Nucleation. (submitted)

Dai, H., Yang, X., Schwarzenberger, K., Heinrich, J., & Eckert, K. (2025). Wettability-dependent dissolution dynamics of oxygen bubbles on Ti64 substrates. International Journal of Heat and Mass Transfer, 236, 126240.

Heinrich, J., Ränke, F., Schwarzenberger, K., Yang, X., Baumann, R., Marzec, M., ... & Eckert, K. (2024). Functionalization of Ti64 via Direct Laser Interference Patterning and Its Influence on Wettability and Oxygen Bubble Nucleation. Langmuir, 40(6), 2918-2929.