Colloid mobilization by fluid displacement fronts in channels

Area of Science:

• Soil Science
• Environmental Science
• Fluid Dynamics

Background:

• Colloid transport in soil is crucial for understanding contaminant movement.
• Existing theories on colloid detachment primarily address saturated soil conditions.
• Mechanisms of colloid mobilization during transient flow (drainage and imbibition) remain underexplored.

Purpose of the Study:

• To theoretically analyze colloid mobilization mechanisms under transient flow conditions.
• To investigate the influence of adhesion, drag, friction, and surface tension on colloid detachment.
• To experimentally validate theoretical predictions using microspheres in controlled channels.

Main Methods:

• Theoretical force and torque analyses were conducted to model colloid mobilization.
• Colloid and substrate contact angles were varied to establish mobilization criteria.
• Experiments utilized confocal microscopy to observe microsphere mobilization during simulated drainage and imbibition.

Main Results:

• Colloid mobilization varied significantly between drainage and imbibition due to dynamic contact angles and interfacial geometry.
• Theoretical models predicted mobilization mechanisms including lifting, sliding, and rolling.
• Experimental observations partially aligned with theoretical criteria, with deviations attributed to factors like aggregates and trailing films.

Conclusions:

• Transient flow conditions significantly impact colloid mobilization dynamics in soil.
• Both theoretical and experimental approaches indicate that lifting, sliding, and rolling collectively contribute to colloid mobilization.
• Further research incorporating factors like aggregates and films is needed for comprehensive models.