Egor Bersenev | Scattering in soft matter physics

We have investigated the humidity-responsive structure of polymer–surfactant multilayer nanofilms composed of a hydrophilic maleic acid polymer and an amphoteric amine oxide surfactant (C12-AO). Neutron reflectometry (NR) revealed the presence of a smooth thin film comprising several surfactant bilayers intercalated with the polymer. Upon exposure to increased humidity, the nanostructured film reorganized into a vertically stratified multilayer structure with polymer chains located in the vicinity of hydrated surfactant headgroups, with further humidity increase leading to the formation of surfactant-rich domains, indicating a high mobility of the surfactant molecules in the polymer matrix. Off-specular neutron reflectometry and grazing-incidence X-ray scattering revealed the presence of surfactant nanocrystals in the as-prepared film, which diffused to form surfactant-rich domains upon exposure to humidity, thus providing a reservoir of surfactants. These findings help elucidate a mechanism of structural transformation in dried polymer–surfactant films, thus suggesting an avenue for engineering an antimicrobial coating with longevity and a humidity-activated release of active molecules using two-dimensional confinement effects.

We investigated the structure of polymer-surfactant aggregates and their pH-dependent structural evolution using hydrophobically modified poly(vinyl-pyrrolidone) (h-PVP) and sodium dodecyl sulfate (SDS). The structure of the complexes in the weak (pH ≃ 9) and strong (pH ≃ 2) interaction regimes was studied using small-angle X-ray scattering, with the data analysed on an absolute intensity scale, using molecular parameters as constraints. At pH 9, where self-assembly was driven by hydrophobic interactions, we have found that, at low surfactant concentrations, elongated aggregates were formed. At excess surfactant concentrations, the aggregates became more compact with a smaller aggregation number, resembling free micelles with the hydrophobic domains of the polymer incorporated into the surfactant core. In all cases, aggregates formed a continuous network, with polymer serving as a weak cross-linker between aggregates. Finally, we have compared the structure of these weakly interacting aggregates with the precipitates formed at low pH, where the electrostatic attraction dominates.

Brush-like elastomers with crystallizable side chains hold promise for biomedical applications requiring the presence of two distinct mechanical states below and above body temperature: hard and supersoft. The hard semicrystalline state facilitates piercing of the body whereupon the material softens to match the mechanics of surrounding soft tissue. To understand the transition between the two states, the crystallization process was studied with synchrotron X-ray scattering for a series of brush elastomers with poly(ε-caprolactone) side chains bearing from 7 to 13 repeat units. The so-called bottlebrush correlation peak was used to monitor configuration of bottlebrush backbones in the amorphous regions during the crystallization process. In the course of crystallization, the backbones are expelled into the interlamellar amorphous gaps, which is accompanied by their conformational changes and leads to partitioning to unconfined (melt) and confined (semicrystalline) (conformational) states. The crystallization process starts by consumption of the unconfined macromolecules by the growing crystals followed by reconfiguration of macromolecules within the already grown spherulites.