Hydrophilic Materials Lead the Way in Subsurface Oil Management
In the shifting landscape of groundwater remediation and subsurface engineering, researchers at the Korea Institute of Science and Technology (KIST) have turned a long‑standing assumption upside down.
Their detailed microfluidic observations and analytical modelling reveal that hydrophilic materials, surfaces that attract water, retain more oil under groundwater‑like conditions than the traditionally favoured hydrophobic materials.
Breaking away from conventional wisdom
It’s long been accepted that hydrophobic materials, which repel water, excel at attracting and holding oil, making them the go‑to option for oil separation. Yet KIST’s Dr Seunghak Lee, Jaeshik Chung, and Sang Hyun Kim found the opposite in specific subsurface scenarios.
Using a precision microfluidic system, a “lab‑on‑a‑chip”, they recreated porous media conditions under constant pressure differentials that closely mimic natural groundwater flows.
What they witnessed was striking: oil slid away from hydrophobic surfaces, while hydrophilic materials trapped and held oil in significant amounts.
Understanding the science
In hydrophobic media, the contact angle where water repels oil is larger than in hydrophilic environments. This reduces the capillary pressure drop but increases the viscous pressure difference, speeding up the water flow within the pores. Faster pore‑flow effectively sweeps oil away.
By contrast, hydrophilic surfaces reduce the contact angle, slow the velocity of water, and provide a kind of safe haven for oil pockets. Under identical pressure conditions, oil is far less likely to be flushed out.
Pore geometry plays its own role. Irregular microstructures within hydrophilic media can fragment oil clusters, sometimes reducing retention but often enhancing water permeability, reinforcing that “hydrophobic” does not always mean “better” under dynamic conditions.
Real-world implications for remediation
This study offers a fresh framework for understanding contaminant migration and settling in groundwater. The findings could reshape how engineers design Permeable Reactive Barriers (PRBs) at polluted sites such as military bases or petrol stations.
Dr Jaeshik Chung noted: “Groundwater remediation is not just a matter of materials science, but a representative multiphysics phenomenon that involves a complex interplay of fluid flow and interfacial reactions.”
The applications extend beyond remediation. Dr Chung highlighted that similar principles apply to enhanced oil recovery (EOR) and carbon capture and storage (CCS).
Dr Seunghak Lee added: “This achievement shows that underground fluid flow can behave completely differently from existing scientific theories under certain conditions … This research lays the scientific foundation for more precise control of the underground environment.”
Global context and comparisons
The global oil‑water separation sector has leaned heavily on hydrophobic solutions:
- Superhydrophobic copper meshes are effective for surface oil skimming, though they behave differently below ground.
- Smart nano‑sponges can switch wettability under UV light, making them ideal for surface clean‑up but less suitable for subterranean conditions.
- Biomimetic materials inspired by the Salvinia effect can trap air and lift oil but are generally applied above the water table.
None of these approaches addresses the subtleties KIST uncovered under continuous subsurface pressure flows.
For industry
For site engineers, environmental consultants, and policymakers, this isn’t just a scientific novelty, it’s a practical insight that can improve pollution prevention strategies, optimise remediation costs, and extend the life of subsurface containment systems.
By re‑evaluating material choices, projects can achieve more reliable oil containment in PRBs and other groundwater management systems. Oil recovery operators and CCS project designers can also fine‑tune operations for better efficiency and environmental safety.
Looking ahead
KIST’s work highlights the need to approach subsurface engineering with a deeper understanding of multiphysics interactions. Material selection should be based on how surfaces behave under realistic conditions, not solely on conventional theories.
By prioritising performance under dynamic groundwater‑like conditions, the industry can move towards more sustainable and effective oil control measures—whether for remediation, recovery, or storage.
