Chemical Engineering Seminar
Liquids, like solids, have tensile strength. Indeed, biologists have long believed that plants exploit this strength to pull water out of the soil and up to their leaves during transpiration, with the pressures in the sap dropping to as low as -100 bar (i.e., tensions up to 100 bar). Nonetheless, the role of liquid water under tension in transpiration has remained controversial. Furthermore, the properties of this metastable liquid state have been explored only sparsely in other scientific and technological contexts. In this talk, I will discuss the physics of transpiration and the known physiological elements of xylem (the vessels through which water flows) that are believed to play important roles in its operation. I will translate these concepts into engineering principles and introduce our approaches to form synthetic systems that recapitulate important aspects of the form and function of xylem. Based on experiments with our "synthetic plants," I will illustrate the surprising processes that are enabled by borrowing designs from plants. In the context of heat transfer and environmental sensing, I will present theoretical arguments for the advantages of developing technologies that exploit liquids under tension. I will finish by presenting the interesting dynamics of cavitation (boiling) in porous media that mimic xylem structure, with a discussion of implications for plant physiology, water in the geological subsurface and technologies based on metastable liquids. Throughout, I will point to outstanding technical and fundamental questions related to this regime.