Stability, adsorption and electrokinetic properties of the chitosan/silica system

Abstract

The aim of this paper was to analyze stability, adsorption and the electrokinetic properties of suspensions containing chitosan and silica. Chitosan (Ch), the second most abundant natural polysaccharide, biodegradable and relatively cheap can be very good alternative for artificial polymers used in the stabilization of metal oxide suspensions. The results obtained from spectrophotometric and turbidimetric stability measurements proved that the higher concentrations of chitosan the more stabile the silica suspensions. The mechanism of the stabilization is the electrosteric one because the studied polymer not only adsorb on the silica surface but also possesses amino groups creating additional charge barrier preventing from flocculation. The adsorption of chitosan increases also with the increase of pH of the solution. However, the protonation of this polymer is the highest in pH = 5–6.3 and as the consequence in the above mentioned pH stabilization of the silica suspensions is the best. There is no significant influence of chitosan molecular weight on stability of studied suspensions when concentration of the polymer is relatively low (60 ppm–120 ppm). However, for higher concentrations of chitosan (200 ppm–800 ppm) stability increases with the increase of its molecular weight as well as the adsorption of this polymer on the silica surface. The additional information about stability and the structure of the adsorption layer was obtained from the zeta potential measurements. The presented results can find practical applications connected with functionalized materials especially in medicine, pharmacy, cosmetics and agriculture.