Investigation on the flow behavior of dispersions of solid triglyceride nanoparticles.

The flow behavior of low concentrated dispersions of solid lipid nanoparticles consisting of either trimyristin, tripalmitin or tristearin and different ionic and nonionic stabilizer blends were investigated using a rheometer with cone and plate apparatus and an Ubbelohde type capillary viscometer. The data demonstrate a remarkable influence of the matrix material, the stabilizer composition and the presence of small amounts of sodium chloride on the formulations' rheological properties. A significant increase in dispersion viscosity was found in the triglyceride sequence trimyristin < tripalmitin < tristearin. This effect can be clearly attributed to an increase in particle shape anisometry with increasing length of the lipid's fatty acid chains. Surfactants, which are present during the crystallization of the dispersed lipid seem to have an additional effect on the nanoparticle shape. Beyond this, ionic surfactants and other salts affect the dispersion viscosity by altering the dimension of the electrical double layer ("second electroviscous effect").