Synopsis: Mind the Interface

A spectroscopic technique reveals the molecular structure of a charged water interface.
Synopsis figure
Y.-C. Wen et al., Phys. Rev. Lett. (2016)

The interfacial layer between water and a charged surface can have a rich chemistry in which water molecules and ions interact via hydrogen bonding and electrostatic forces. Such interfaces are ubiquitous in nature and play a key role in energy-conversion applications, such as water splitting for fuel cells. Determining the exact chemical structure of a charged interface layer is, however, challenging with most probes because the signal from the interface is entangled with that of the underlying bulk water layer. Now, researchers have developed a new spectroscopic technique that extracts information about the interface layer by carefully separating out the signal from the bulk layer. This technique can be used to reveal the molecular structure of complex biological or electrochemical interfaces.

Chuanshan Tian, at Fudan University in China, and his colleagues prepared a single-molecular layer of lignoceric acid (C23H47COOH) on top of water, creating an interface with varying amounts of surface charge. Using lasers, the team measured the combined molecular vibrational signal from water molecules—in the bulk layer and in the interface layer—and from the lignoceric acid molecules. The researchers were able to separate out the bulk signal contribution by characterizing, for the first time, a second-order optical property of water that had been previously known but never quantified. With this approach, Tian and his team were able to measure the geometry and strength of the molecular bonds in the charged interface layer. They showed that the molecular structure in this region depends strongly on the pH and ionic makeup of the surrounding medium.

This research is published in Physical Review Letters.

–Katherine Kornei


More Features »


More Announcements »

Subject Areas

Chemical PhysicsBiological Physics

Previous Synopsis

Atomic and Molecular Physics

Cooler Colliders

Read More »

Next Synopsis

Materials Science

Growing Crystals in Macrosteps

Read More »

Related Articles

Synopsis: Racing Bacteria
Biological Physics

Synopsis: Racing Bacteria

Bacteria track fast-moving chemical signals by hopping from one chemically favorable region to another. Read More »

Synopsis: Cell Sensing Improves in a Loose Crowd
Biological Physics

Synopsis: Cell Sensing Improves in a Loose Crowd

Cells that communicate with each other can measure chemical concentrations with higher precision if they spread out into a sparse configuration.   Read More »

Focus: Membrane Holes Can Shrink, Grow, or Stay Put
Soft Matter

Focus: Membrane Holes Can Shrink, Grow, or Stay Put

Pores in a polymer film do not change size over time if they have just the right diameter, according to experiments. Read More »

More Articles