Label-free characterization of aqueous micelle nanostructures via novel liquid in-situ Resonant Soft X-ray Scattering (RSoXS)

Micelles are fundamental to nanocarrier applications from drug delivery to environmental remediation. Their structure and dynamics are critical to their properties and functions but are challenging to measure. Here, we demonstrate a novel technique capable of such measurements based on resonant soft X-ray scattering (RSoXS). It uniquely probes organic materials using their intrinsic chemical bonds rather than laborious and disruptive labeling techniques. Our customized microfluidic cell enables RSoXS to be performed in liquid environments, allowing structure and dynamics to be measured in-situ. Using this technique in a multimodal approach, we investigated an amphiphilic polyelectrolyte copolymer micelle of three different molecular weights (Mw). Despite no measurable critical micelle concentration, structural analyses point towards multimeric structures for most Mw’s. The sizes of the micelle substructures are independent of both concentration and Mw. Combining these results with a Mw-invariant surface charge and zeta potential strengthens the link between nanoparticle size and ionic charge in solution that governs polysoap micelle structure. Such control would be critical for nanocarrier applications such as drug delivery and water remediation.