Particle-surface adhesive forces and their role in resuspension phenomena

This project will be undertaken through the EPSRC Aerosol Science CDT with the University of Bristol and the University of Bath.

Resuspension of coarse particles is a significant source of aerosol particles and can pose an enduring health risk (e.g. exposure to dusts after fires or during building works). Entering an area contaminated with a hazardous deposited aerosol adds risk to first responders. Resuspension is also a potential pathogen transport mechanism for agricultural plant disease. If we could predict aerosol resuspension based on activity or environmental changes, the risk to health could be controlled. 

The force required to remove particles from a surface is influenced by van der Waals, capillary and electrostatic forces, as well as environmental conditions (e.g. humidity). To understand this interaction, initial development and experimental validation has been undertaken for a mechanistic, model-based, predictive capability that includes complex particles, surfaces and environmental conditions. Model input parameters include friction velocity, particle size and surface adhesive energy, allowing the user to make predictions with knowledge of the flow over the surface and material properties for a range of atmospheric conditions. The developed predictive resuspension tool (Adaptive Biasi Rock-and-Roll Model) was experimentally validated using hard spherical particles from hard smooth surfaces in dry and humid conditions. The design anticipates future incorporation within hazard prediction to support military and operational decision making. 

Benefitting from complementary expertise in colloid science and aerosols at the universities of Bath and Bristol, the student will apply a variety of techniques to explore the physicochemical factors controlling resuspension of primary particles from surfaces. The project will progress through stepwise increases in experimental complexity coupled with mechanistic model development and validation, exploring different types and morphology of surface, both substrate and particle. 

Specific objectives will include: 

• Develop a range of model surfaces with controlled morphology, hydrophobicity and surface energy, using a combination of techniques such as 3D printing and thin film coating. 
• Measure adhesive force distributions between these surfaces and salt and sugar particles of controlled morphology using colloidal probe atomic force microscopy (AFM). 
• Investigate the effect of environmental humidity on these adhesive force distributions. 
• Implement the measured adhesive force distributions into the mechanistic Adaptive Biasi Rock-and-Roll Model. 
• Assess a subset of identified surfaces and particles in the resuspension wind tunnel. This will validate approaches and relate the single particle interactions investigated by AFM to the complexities of wind tunnel resuspension. 

If initial work with model surfaces and particles is successful, the approach will be extended to include a range of realistic surfaces and particles of interest (e.g. concrete, bacteriological media).