Synergistic Effects of Combinations of Cationic Polyaminoamide Dendrimers/Anionic Polyelectrolytes on Amorphous Silica Formation: A Bioinspired Approach

This paper reports the inhibition efficiency of combinations of amine-terminated polyaminoamide (PAMAM) dendrimers of generation 1 and 2 and anionic polyelectrolytes in colloidal silica particle growth. The polyelectrolytes studied were PAA = polyacrylate (low MW is 2 KDa, high MW is 450 KDa), PAM- co -AA = poly(acrylamide- co -acrylate) of MW 200 KDa, CMI = carboxymethylinulin (proprietary MW, between 2 and 3 KDa). The principle findings are summarized as follows: (1) PAMAM-1 and -2 dendrimers are effective inhibitors of silica growth at 40 ppm dosage levels. (2) The effect of anionic polycarboxylates on the inhibitory activity of PAMAM-1 and PAMAM-2 is dosage-dependent. They do not affect PAMAM-1 inhibitory activity; they increase that of PAMAM-2 at low dosage (20 ppm) but exhibit detrimental effects at high dosage (>40 ppm), with CMI exerting no adverse effects at any dosage. (3) Negative charge density on the polymer is directly proportional to inhibitor activity deterioration. (4) Addition of polymer prevents dendrimer entrapment into the silica colloidal matrix by preventing formation of SiO 2 −dendrimer precipitates. This research was inspired by the recognition that diatom biosilica-associated peptides (silaffins natSil-1 and natSil-2) and long-chain polyamines (LCPA) profoundly influence silica formation from a silicic acid solution in vitro.