The impact of lecithin on rheology, sedimentation and particle interactions in oil-based dispersions

The influence of suspension components on the impact of soybean lecithin on rheological properties of oil-based suspensions was determined and related to sedimentation experiments and force/distance functions from atomic force microscopy (AFM). For that purpose, icing sugar, soda-lime glass or borosilicate glass spheres were dispersed in soybean oil or a medium chain triglyceride (MCT). In case of sugar/oil suspensions (volume fraction ϕ = 0.31), lecithin reduced apparent viscosity and yield stress. In suspensions with soda-lime glass spheres, lecithin did also reduce those parameters whereas it caused a viscosity increase in suspensions of borosilicate glass in soybean oil. Forced sedimentation of sugar suspensions (ϕ = 0.1) revealed that, independent of the dispersant, lecithin significantly reduced the sediment volume whereas an increase was observed for the corresponding glass sphere suspensions. AFM measurements showed that interactions between sugar surfaces dispersed in soybean oil or MCT are dominated by adhesion forces. The addition of lecithin resulted in a reduction of adhesion forces between dispersed sugar particles, which was more pronounced in MCT suspensions. No characteristic changes of the force/distance functions were detected in glass sphere suspensions caused by lecithin.