Two-compartment radial diffusive exchange analysis of the NMR lineshape of Xe129 dissolved in a perfluorooctyl bromide emulsion

Determining chemical exchange rate constants in nanoemulsions using nuclear magnetic resonance

In this work, the second-order kinetics of molecules exchanging between chemically distinct microenvironments, such as those found in nanoemulsions, is studied using nuclear magnetic resonance (NMR). A unique aspect of NMR exchange studies in nanoemulsions is that the difference in molecular resonance frequencies between the two phases, which determines whether the exchange is fast, intermediate, or slow on the NMR timescale, can depend upon the emulsion droplet composition, which is also determined by the kinetic exchange constants themselves. Within the fast-exchange regime, changes in resonance frequencies and line widths with dilution were used to extract the exchange rate constants from the NMR spectra in a manner analogous to determining the kinetic parameters in NMR ligand binding experiments. As a demonstration, the kinetic exchange parameters of isoflurane release from an emulsification of isoflurane and perflurotributylamine (FC43) were determined using NMR dilution and diffusion studies.

Self-assembly and thermoreversible rheology of perfluorocarbon nanoemulsion-based gels with amphiphilic copolymers

Perfluorocarbon (PFC) nanoemulsions have great potential in biomedical applications due to their unique chemical stability, biocompatibility, and possibilities for enhanced oxygen supply. The addition of amphiphilic block copolymers promotes the formation and long-term stability of emulsion-based gels. In this work, we report the systematic study of the impact of adding amphiphilic triblock copolymers to water-in-perfluorocarbon nanoemulsions on their structure and viscoelasticity, utilizing small-angle neutron and X-ray scattering (SANS and SAXS) and rheology. We find that an intermediate concentration of copolymer yields the highest strength of attraction between droplets, corresponding to a maximum in the elasticity and storage modulus. The stability and viscoelastic moduli can be tuned via the amount of copolymer and surfactant along with the volume fraction of aqueous phase. SANS provides the detail on nanostructure and can be fit to a spherical core-shell form factor with a square-well hard sphere structure factor. The PFC nanoemulsion system displays thermoresponsive and thermoreversible properties in temperature sweeps.