Influence of high-molecular-weight water-soluble azacrown ethers on optical properties and structure of the floccules of colloidal gold

Results of experimental study on spectral dependences of absorbance of red gold sol and its floccules in the presence of a selective flocculant (polyazacrown ether) on flocculant concentration and pH of a medium are presented. High selectivity of the adsorption of polyazacrown ether for the particles of colloidal gold in alkaline medium was revealed earlier and it was explained by the formation of coordination bonds of macrocycles with active surface sites. In neutral and acidic media negatively charged colloidal particles form an electrostatic bond with polyazacrown ester macromolecules of positive charge due to the protonation of macrocycle nitrogens. The size of aggregates was calculated by the proposed procedure of evaluation of the sedimentation rate from the data on the reduction of absorbance with time in the maximum at absorbance spectra. The obtained results were controlled by the measurements of the average particle size in the same systems using dynamic light scattering. The obtained dependences of the parameters of the gold sol-polyazacrown ether system (floccule size, quantified parameters of sedimentation, sol color) on the macromolecule charge at the flocculant concentration of 10(-8)-10(-7) mol/l made it possible to qualitatively estimate the structure of the formed floccules and the interaction mechanism of the charged macromolecule of polyazacrown ether with the gold particles.