Faster Nucleation of Ice at the Three-Phase Contact Line: Influence of Interfacial Chemistry.

Controlling the nucleation of ice is important in many areas including atmospheric sciences, cryopreservation, food science, and infrastructure protection. Presently, we conduct controlled experiments and analysis to uncover the influence of surface chemistry at the three-phase line on ice nucleation. We show that ice nucleation is faster upon replacing the air at the water-air interface with oils like silicone oil and almond oil. We show via statistically meaningful and carefully designed experiments that ice nucleation occurs at a higher temperature at an aluminum-water-silicone oil (or almond oil) interface as compared to an aluminum-water-air interface. We show that the location of ice nucleation can be controlled (in situations with multiple locations for ice nucleation) by controlling the interfacial chemistry at the three-phase line. We develop a model (which utilizes classical nucleation theory) to study the combined influence of two interfaces on a seed crystal of ice originating at the three-phase contact line. This model can evaluate the thermodynamic competition between nucleation at the three -phase line and heterogeneous nucleation at an interface. The model shows that three-phase contact lines usually result in a higher driving force than heterogeneous nucleation, which speeds up nucleation kinetics. Overall, our experiments and modeling uncover several useful insights into the influence of three-phase lines on nucleation during contact freezing.

Aluminum-Based Promotion of Nucleation of Carbon Dioxide Hydrates.

Gas hydrate formation has several applications in CO2 sequestration, flow assurance, and desalination. Nucleation of hydrates is constrained by very high induction (wait) times, which necessitates the use of complex nucleation promotion techniques to form hydrates. Presently, we report the discovery of a simple, passive nucleation promotion technique, wherein an aluminum surface significantly accelerates nucleation of CO2hydrates. Statistically meaningful measurements of induction times for CO2 hydrate nucleation were undertaken using water droplets as individual microsystems for hydrate formation. The influence of various metal surfaces, droplet size, CO2 dissolution time, and the presence of salts in water on nucleation kinetics was characterized. Interestingly, we observe nucleation initiation only on aluminum surfaces, the influence of which cannot be replicated by salts of aluminum. We discover that the aluminum-water interface is responsible for nucleation promotion. We hypothesize that hydrogen bubbles generated at the aluminum-water interface are responsible for nucleation promotion.