Polymorph Dispersed Particles from the Bicontinuous Cubic Phase of Glycerol Monooleate Stabilized by PEG‐Copolymers with Lipid‐Mimetic Hydrophobic Anchors

Abstract

Four unique nonionic block‐copolymers have been tested as dispersants and stabilizers for dispersed particles from the bicontinuous cubic phase of glycerol monooleate, GMO. The polymers have hydrophilic blocks composed of PEO with 52 to 136 EO units. These are linked via ether bonds to lipid mimetic hydrophobic anchor groups, bearing between two and eight dodecyl chains. The polymer with the longest PEO block is a triblock polymer, with hydrophobic anchors at both ends. The polymers are taken up by the cubic phase of GMO, and their effect on the swelling of this phase in water was investigated. The excess aqueous solution above the cubic phase was found to contain dispersed particles in varying amounts, depending on polymer type and concentration. The structure and morphology of these colloidal particles were investigated by cryogenic transmission electron microscopy (cryoTEM). Besides dispersed particles of the cubic phase, various types of vesicles and particles with disordered interior were observed, as well as in some systems more peculiar structures, e.g, a honeycomb structure. Particle dispersions were also prepared via a precursor dispersion of the GMO‐polymer mixtures in glycerol. The particles resulting from a dilution of this precursor dispersion in a ten‐fold excess of water were examined with cryoTEM. Using low proportions of the polymers, dispersed cubic particles were obtained, although only occasionally shaped as small cubes. Usually the particles were very polydisperse in both size, shape, and morphology. In some systems large amounts of particles with a disordered interior, reminiscent of particles from a sponge phase, were observed. At higher concentrations of the polymers, vesicles of various morphologies were most abundant, and at highest concentrations of the most hydrophobic polymers, band‐shaped micellar structures appeared together with vesicles. Since these polymers were sparingly soluble in water, the band‐shaped micelles are probably mixed micelles containing GMO and the polymer. The packing of the polymers and their effects as steric stabilizers are discussed and related to the Flory measure of their size.

Keywords:

• Bicontinuous cubic phase
• cubosome
• vesicle
• liquid crystal nanoparticle
• cryoTEM
• glycerolmonooleate
• block copolymer

Acknowledgments

Financial support from the Swedish Research Council is gratefully acknowledged. We thank G. Karlsson for help on advice in the cryoTEM investigations.