Herein, we explore the interactions of monovalent and divalent Hofmeister series metal cations with negatively charged surfactant monolayers at the air/water interface using infrared-visible sum frequency generation (SFG) vibrational spectroscopy. Employing SFG allows one to explore (1) the interfacial water structure, (2) the hydration and orientation of the headgroup on the surfactant molecules, as well as (3) the ordering and orientation of the surfactant alkyl chains. Understanding the rules that govern cation binding to anionic headgroups is complex, as these depend on a large number of factors that include solution pH, temperature, the nature of the anionic head group and cation, as well as the charge density at the interface. In this presentation, we will explore the relative importance of each of these factors and look at the physical-chemical patterns that help determine the strength and nature of binding interactions.

The interactions of metal cations with negatively charged surfactants in Langmuir monolayers

ACS Fall 2021

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