Structures formed by interactions in solid dispersions of the system polyethylene glycol-griseofulvin with charged and non charged surfactants added

Abstract

Solid dispersions of polyethylene glycol (PEG) 3000 and 10% w/w griseofulvin with incorporation of different types of surfactants were prepared by the melting method. The anionic surfactant sodium dodecyl sulphate (SDS), the cationic surfactant dodecyltrimethylammonium bromide (DTAB) and the nonionic surfactant polyoxyethylene dodecyl ether (Brij) were added in equivalent amounts. Phase analysis was made by X-ray powder diffraction and investigation of the short-range structure by 13C-CP/MAS solid-state NMR. The addition of the different types of surfactants influences the structure of the dispersions in a varying manner. The anionic surfactant SDS forms a solid solution, the nonionic Brij does not influence the particulate dispersion and the cationic DTAB creates a dispersion, that only to a certain extent is a solid solution. The extent of interaction between polymer and surfactant aggregates (micelles) seems to be crucial for the formation of solid solutions of griseofulvin in the polymer phase. The charged surfactants can interact with the polymer forming aggregates, while the nonionic ones show no interaction. When a solid solution is formed, the hydrophilic parts of the griseofulvin molecule are significantly influenced. The surfactant aggregates bind griseofulvin in a molecular form at the surface or, more probably, in the interior of the aggregate.