Study of colloids transport during two-phase flow using a novel polydimethylsiloxane micro-model

Area of Science:

• Environmental Science
• Fluid Dynamics
• Materials Science

Background:

• Colloid transport in porous media is crucial for understanding contaminant and nutrient movement in subsurface environments.
• Existing knowledge on colloid removal and remobilization under unsaturated conditions is limited, particularly concerning the role of fluid-fluid interfaces.
• Transient two-phase flow conditions significantly influence colloid behavior, yet the underlying mechanisms remain poorly understood.

Purpose of the Study:

• To investigate colloid transport and remobilization mechanisms within a porous medium under transient two-phase flow conditions.
• To visualize and quantify colloid behavior at the pore scale using a novel microfluidic device and advanced imaging techniques.
• To elucidate the role of fluid-fluid interfaces in the mobilization of deposited colloids.

Main Methods:

• Fabrication of a closed microfluidic device using polydimethylsiloxane (PDMS) to simulate a porous medium with uniform hydrophobic properties.
• Utilized confocal microscopy for real-time visualization of fluorescently labeled colloid movement and fluid flow within the micro-model.
• Quantified colloid concentrations in effluent using fluorescence intensity measurements to generate breakthrough curves.

Main Results:

• Successfully visualized the remobilization of attached colloids by moving fluid-fluid interfaces within the microfluidic network.
• Observed a peak concentration in the effluent breakthrough curve coinciding with a drainage event, indicating colloid release.
• Demonstrated the effectiveness of the PDMS micro-model and confocal microscopy for studying colloid retention and mobilization under transient flow.

Conclusions:

• The combination of a PDMS micro-model and confocal microscopy provides a powerful tool for visualizing pore-scale colloid transport.
• Fluid-fluid interfaces play a significant role in the remobilization of colloids during transient two-phase flow.
• This study enhances the understanding of colloid dynamics in unsaturated porous media, with implications for environmental remediation and resource management.