Tunable Nanostructures from Inverse Surfactants

TL;DR

This paper investigates how molecular parameters influence the self-assembly of inverse surfactants, combining experiments, simulations, and theory to map their morphological phase diagram and guide the design of supramolecular structures.

Contribution

It introduces a minimal theoretical framework that explains the morphological transitions of inverse surfactants based on molecular size ratios and experimental insights.

Findings

Changing head-group size controls morphological transitions.

The size ratio of hydrophobic to hydrophilic groups determines micelle structure.

The theory explains the prevalence of fiber-like structures.

Abstract

Hierarchical materials in the natural world are often made through the self-assembly of amphiphilic molecules. Achieving similar structural complexity in synthetic materials requires understanding how various molecular parameters affect assembly behavior. In recent years, inverse surfactants -- molecules with hydrophobic head groups and hydrophilic macromolecular tails -- have been shown to self-assemble into supramolecular assemblies in aqueous solutions that show promise for a number of applications, including drug delivery. Here, we build an understanding of the morphological phase diagram of inverse surfactants using insights from scattering experiments, computer simulations, and statistical mechanics. The scattering and simulation results reveal that changing the head-group size is an important molecular knob in controlling morphological transitions. The molecular size ratio of the hydrophobic group to the hydrophilic emerges as a crucial dimensionless quantity in our theory and plays a determining role in setting the micelle structure and the transition from mesoscale to macroscale aggregates. Our minimal theory is able to qualitatively explain the key features of the morphological phase diagram, including the prevalence of fiber-like structures in comparison to spherical and planar micelles. Together, these findings provide a more complete picture for the molecular dependencies of assemblies of inverse surfactants, which we hope may aid in the de novo design of supramolecular structures.