Induced Crystallization of Polyelectrolyte-Surfactant Complexes at the Gas-Water Interface

TL;DR

This study reveals how minute surfactant concentrations induce the formation of structured polyelectrolyte-surfactant complexes at the gas-water interface, with detailed structural insights obtained through synchrotron X-ray techniques.

Contribution

It provides new detailed structural characterization of PE-surfactant complexes at interfaces using advanced X-ray methods.

Findings

Surfactant induces a liquid-like monolayer at the interface.

Salt addition leads to formation of distorted-hexagonal columnar crystals.

Water structure at the interface is notably disrupted.

Abstract

Synchrotron-X-ray and surface tension studies of a strong polyelectrolyte (PE) in the semi-dilute regime (~ 0.1M monomer-charges) with varying surfactant concentrations show that minute surfactant concentrations induce the formation of a PE-surfactant complex at the gas/solution interface. X-ray reflectivity and grazing angle X-ray diffraction (GIXD) provide detailed information of the top most layer, where it is found that the surfactant forms a two-dimensional liquid-like monolayer, with a noticeable disruption of the structure of water at the interface. With the addition of salt (NaCl) columnar-crystals with distorted-hexagonal symmetry are formed.