Surfactant-triggered disassembly of electrostatic complexes probed at optical and quartz crystal microbalance length scales

TL;DR

This study investigates how surfactants trigger the disassembly of electrostatic nanostructures, revealing mechanisms at both nanoscale and microscale levels using quartz crystal microbalance and optical microscopy.

Contribution

It provides new insights into the disassembly process of electrostatic complexes induced by surfactants, combining multi-scale analysis techniques.

Findings

Disassembly begins at the wire surface with nanoparticle release.

Swelling and erosion lead to complete wire dissolution.

Disassembly process confirmed at both nanoscale and microscale.

Abstract

A critical advantage of electrostatic assemblies over covalent and crystalline bound materials is that associated structures can be disassembled into their original constituents. Nanoscale devices designed for the controlled release of functional molecules already exploit this property. To bring some insight into the mechanisms of disassembly and release, we study the disruption of molecular electrostatics based interactions via competitive binding with ionic surfactants. To this aim free-standing micron-size wires were synthesized using oppositely charged poly(diallyldimethylammonium chloride) and poly(acrylic acid) coated iron oxide nanoparticles. The disassembly is induced by the addition of sodium dodecyl sulfates that complex preferentially the positive polymers. The process is investigated at two different length scales: the length scale of the particles (10 nm) through the Quartz Crystal Microbalance technique, and that of the wires (> 1 micron) via optical microscopy. Upon surfactant addition, the disassembly is initiated at the surface of the wires by the release of nanoparticles and by the swelling of the structure. In a second step, erosion involving larger pieces takes over and culminates in the complete dissolution of the wires, confirming the hypothesis of a surface-type swelling and erosion process.