Influence of polyelectrolytes on lecithin–based w/o microemulsions and BaSO₄-nano particle formation

Abstract

The chapter describes the behavior of polymer-modified phospholipid-based w/o micro emulsions and its use for nanocrystal synthesis. We focused our interest on the naturally occurring crude soybean lecithin in presence of isooctane and water. In the case of the unmodified system an isotropic inverse micellar region can be observed in the oil corner. By adding an anionic polyelectrolyte, i.e., sodium polyacrylate, the area of the optically clear phase is drastically decreased. The incorporation of the neutral polymer poly(ethylene glycol) (PEG), and the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) induces the formation of an isotropic narrow phase channel in the area of the origin L₂ phase. The cationic poly(ethyleneimine) can be incorporated much better up to polymer concentrations of 5 wt%. From ¹H NMR self-diffusion experiments one can conclude that the isotropic phase is indeed a reverse micellar microemulsion. Rheological experiments show a non-Newtonian flow behavior of the microemulsions. By means of differential scanning calorimetry (DSC) bulk water can be detected in the reverse w/o droplets. In comparison to the natural soybean lecithin, a pure phosphatidylcholine (>95%), modified with sodium dodecylsulfate, and/or PDADMAC was investigated. The reverse microemulsion droplets were used as a template phase for the synthesis of BaSO₄ nanoparticles. The polymers involved in the redispersion process, influence the size, and supramolecular arrangement of the nanoparticle composites formed.

Acknowledgements: The authors thank Erich Kleinpeter and Gunter Wolf for the ¹H NMR self-diffusion experiments, as well as Helmut Cölfen and Robert Menzel for the ultracentrifugation measurements. Finally we thank Stephen Mann for his stimulating discussion about the “EM-holes”. The company PHOSPHOLIPID GmbH is gratefully acknowledged for the supply of phospholipon.