Structure-property evaluation of poly(ethylene glycol) surfactants and nanostructured fluids

Hypothesis: The development of nanostructured fluids with tailored structure-properties relationships is pivotal for countless applications from pharmaceuticals to Cultural Heritage preservation. However, the refinement of a formulation often relies on multiple development steps resulting in high time consumption. To overcome this limitation, knowledge of the surfactant physico-chemical properties at the “single-chain” level is crucial for predicting the formation of nanostructured fluids, as well as their hydrodynamic behavior. Here, we propose a robust, accessible methodology to evaluate the polymer-solvent interactions of surfactants, enabling effective investigations of their properties, which can serve applications such as the formulation of complex fluids, polymer films preparation, degradation, and swelling behavior. Experiments: A series of bio-derived PEG-based surfactants bearing different end-chain functionality were investigated by size exclusion chromatography and nuclear magnetic resonance to evaluate their structure and diffusion coefficient in selected solvents. The PEG dynamics were furthermore correlated to nanostructured fluid's formation and hydrodynamic properties by nuclear magnetic resonance and small-angle x-ray scattering. Findings: The surfactants' structural and hydrophilic/hydrophobic features, namely molar mass, end-group functionalization, logP and hydrodynamic behavior in water and organic solvents, correlated well with the micelles' hydrodynamic and structural features. The selection of organic solvent in the nanostructured fluids, i.e. acetone or tetrahydrofuran, determined controlled variations of the fluids' structural features. As a result, the surfactant's properties could be easily tailored to enhance parameters such as solvent encapsulation and hydrodynamic radii. The structure-property correlations enabled the development of tailor-made, sustainable systems with bio-derived surfactants for potential application in numerous transversal fields where micelles are employed.