Turbidimetric studies of colloidal silica/aqueous solution system stability

The effects of solid content, temperature, supporting electrolyte (sodium chloride (NaCl)) concentration, solution pH, molecular weight of synthetic non-ionic polymer, natural polymer addition and synthetic copolymer presence on the silica suspension stability were examined. The natural proteins – human serum albumin and lysozyme (LSZ) – as well as the exopolysaccharide synthesized by soil bacterium Sinorhizobium meliloti 1021 were used. Moreover, synthetic homopolymers – non-ionic poly(vinylpyrrolidone) and copolymers of polyamino acids with poly(ethylene glycol) – were applied. The turbidimetric method was used to monitor the colloidal silica aqueous suspension stability as a function of time. LSZ and copolymers containing polylysine at the basic values of solution pH have the greatest effect on system destabilization. The negative surface charge neutralization by the positively charged groups of the polymeric chains is mainly responsible for such behavior of the systems under examination. On the other hand, the synthetic polyvinylpyrrolidone causes considerable improvement of silica suspension stability. Its adsorption on the solid particles surface causes efficient stabilization due to steric repulsion occurrence.