Microfluidic experiments allow for precise control of both fluid flow conditions and channel geometric parameters, creating ideal test-beds for exploring complex multi-phase phenomena. In this work, I design microfluidic channels lined with microscale pores for study of multiphase phenomena including capillary displacement of oil, thin film flows over geometric features, geometrical effects on phase change (dissolution), and remediation of water pollutants.

Perfluorinated (PFAS) compounds are ideal for imparting hydrophobic properties to a variety of materials including non-stick cookware, water repellent clothing, and fire fighting foam. However, these compounds are environmentally persistent and toxic to both humans and to ecosystems. In this project, we use naturally derived materials to create alternative hydrophobic coatings that can replace PFAS chemicals.

Superhydrophobic surfaces have generally proven unsuccessful at eliminating fouling in real world sources of water. In this project, drops of water containing dissolved minerals important in the environment are evaporated on a number of different engineered materials to probe the anti-fouling properties of the underlying substrates. We discovered that there is a critical length scale for superhydrophobic surfaces to be able to successfully repel crystals and prevent fouling. When surfaces are designed with features below this critical length scales, we are able to induce self ejection of crystals.

When a drop of volatile liquid containing particles or solutes evaporates on a surface, it leaves behind those particles/solutes in patterns on the surface. The pattern left depends on the evaporation rate, inter-particle interactions, and Marangoni recirculation. In this project, I explore how the wettability and texture of the substrate influence patterning for an aqueous drop of water containing dissolved salts. In addition to exploring substrate interactions, I also investigate how different properties of salts can lead to previously unexplored phenomena. 

Crystallization is enhanced at interfaces due to heterogeneous nucleation. Thus, engineered interfaces can be used to increase crystallization kinetics or to selectively control for specific polymorphs. Properties that can be altered include substrate chemistry, surface energy, texture, and porosity. We apply these techniques to selectively precipitate useful chemistries from waste streams. Another aspect of this project is using the same principles to create surface that eliminate crystal fouling in water treatment and/or desalination. 

Biofilms form when bacteria or fungi colonize a surface by creating a rigid extracellular matrix that enables survival of the colony. Biofilms are problematic in water treatment and pose a risk to human health, as they enable contagious bacteria to remain viable outside of a host and create opportunities for new infections when people come into contact with an infected surface. Dr. McBride previously contributed to a Space Biofilms project led by Dr. Luis Zea that characterized biofilm formation onboard the International Space Station in response to nanoengineered and liquid infused surface. Currently, the McBride research group is working in collaboration with Professor Howard Stone at Princeton on a new space station project that will explore the dynamics of pellicle (biofilms at air/water interfaces) formation in microgravity.

Shearing flows have a large impact on chemical kinetics and phase change. However, shear-induced mixing alone may not be the only factor leading to dramatic increases in chemical kinetics. Past work in this area discovered that a combination of shearing flows and  interfacial phenomena are especially powerful in altering kinetics and phase change. In that work, shearing flows were imposed using a Coutte device on a solution of native protein to trigger deformation and regrowth into amyloid fibers. We demonstrated that shearing forces alone are insufficient to result in protein deformation. Future work in this area will use microfluidic devices to explore reaction rates for environmental processes as a function of fluid flow.