Thursday, July 31, 2014

Superheating a Liquid to Create a Single Bubble

Image Credit: thinkstockphotos.com/assistantua
When a superheated material begins the transition from one phase to the next (like liquid to gas), small bubbles can form, a process called bubble nucleation. Scientists at Harvard have presented a new method for studying superheated materials in the moments before, during, and after bubble nucleation.

There are various ways to study superheating liquids and bubble nucleation. This method involves studying individual bubbles rather than a large number all at once. The scientists began by creating a single nanopore in a membrane and surrounding it in a sodium-chloride solution. A small voltage pulse passed across the membrane and rapidly heated the surrounding liquid. A single bubble of vapor evenly formed in the center of the small pore of the membrane before collapsing approximately 16 nanoseconds (ns) later. Another bubble formed 120 ns after that.

A cross section of the experimental setup. The gap between the two plates is the nanopore where the bubbles are formed.
Image Credit: Phys. Rev. Lett. 113, 024506
The scientists used two methods to study the creation and evolution of the bubbles: measuring the current, and using optical measurements. When the bubble formed on the membrane, it temporarily blocked the flow of ions across the pore. While measuring the electrical signal, a laser pointed at the center of the nanopore and scattered when a bubble formed.

As scientists continue to study bubble nucleation, one of the most exciting future applications of knowing more about bubble nucleation are using bubbles as lenses. In using bubbles, there's the potential to move or change a lens to rapidly refocus light. Learning more about bubble nucleation also has applications in chemistry, electronics, acoustics, and characterizing certain states of matter.

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