New insights into how salt gathers at common solvent surfaces

New research from Flinders University has shed light on one of chemistry's big mysteries by describing how simple salts exist near the surface of liquid solvents.

In a new international collaborative study, experts used a technique called ion scattering spectroscopy on a range of solvents to understand the interface between air and water droplets in the atmosphere.

Dr Gunther Andersson, professor of chemical physics and nanotechnology at Flinders University, says the new method largely describes how ions form simple salts present in the outer layer of dissolved solvents, such as common table salt ((sodium chloride) (On⁺ and Cl^– or NaCl).

Article “Ion specificity on the surface of solvents: depth profiles of monovalent inorganic ions.” published V Journal of Colloidal and Interface Sciencepaves the way for further understanding of key environmental processes.

“This question has remained unresolved for decades, and this study is an important step forward in understanding chemical reactions in the atmosphere where water drops meet air, reactions that have environmental implications,” says lead author Professor Andersson from the Flinders Institute for Nanoscale Science and Technology in the College of Science and Technology.

“Ion scattering spectroscopy can be simplistically described as a game of billiards with atoms, where the billiard balls (atoms) have different masses from the entire periodic table.

“There is no other method that can comprehensively examine this problem.”

First author Dr Anand Kumar, a CSIRO research fellow now working at the Paul Scherrer Institute in Switzerland, says the research team now hopes to use the technique to study how it applies to water, where it matters most. solvent.

“We are creating a solvent scale based on surface tension to evaluate and hopefully predict in the future which ions will make it to the outer layers and which will not,” says Dr. Kumar.

“On this scale, water is at the other end, and with further research we will test how this scale plays out for water.”

In the latest study, neutral collisional ion scattering spectroscopy was used to directly measure the depth concentration profiles of monovalent inorganic ions (Cl⁻Br⁻I⁻already⁺TO⁺and Cs⁺) in solution in four non-aqueous solvents – propylene carbonate (PC), benzyl alcohol (BA), glycerol and formamide (FA).