Heterogeneous micellar solubilization within lyotropic liquid crystals interfaces

Abstract

The solubilization of sodium diclofenac (Na-DFC) in a glycerol mono-oleate-based emulsion triggers structural changes. A reverse hexagonal mesophase forms at 2–5 wt% Na-DFC. Above 6 wt%, the hexagonal symmetry gradually transitions to a disordered lamellar mesophase at 9 wt%. These structural shifts impact the storage modulus, structuring enthalpy, and structural diffusivity of the system. Despite these transitions, the driving force for Na-DFC release remains consistent, leading to hypothesize that the interfacial structure remains unchanged during Na-DFC release.The nano-structural modifications imposed by the Na-DFC load and release were assessed by small-angle X-ray diffraction (SAXD), spin-probe electron paramagnetic resonance (EPR), and nuclear quadrupole resonance (NQR).The selective solubilization of Na-DFC was demonstrated in the SAXD peak fittings, revealing an increase in hexagonally oriented rods at the expense of non-oriented micelles, rather than gradual micellar elongation. Computation of the EPR spectra also showcased the selective solubilization of Na-DFC at an enhanced free energy interface (γ), evidenced by step-wise variations in polarity, microviscosity, and order parameters. Additionally, NQR analysis highlighted a higher anisotropy for sodium compared to deuterium, linking the selective solubilization of Na-DFC to heterogeneous structural transformations. These findings underscore the heterogeneous nature of solubilization-release processes, driven by locally increased micellar free energy. Consequently, the loaded Na-DFC interfaces maintain a constant γ, ensuring a consistent release driving force despite structural transitions affecting the matrix. The ability to selectively solubilize guest molecules may herald a new era in the utilization of selective molecular interfacial loading.