Mechanism of selective interaction of high-molecular-weight water-soluble azacrown ethers with particles of colloidal gold

Results of experimental study of absorption spectra of red gold sol and its flocs in the presence of selective flocculant (polyazacrown ether, PACE) reported in [1] are discussed. The observed differences in parameters of gold sol-polyazacrown ether system as dependent on the macromolecule charge in the range of low polymer concentrations makes it possible to determine the driving forces and optimal conditions of a selective effect of polyazacrown ether: at low pH values, the flocculating effect of a polymer is nonspecific and is accounted for by the reversible electrostatic interaction with colloidal particle. At large pH, the selective modifying effect of PACE is due to strong coordination bonding of macromolecules with the particles and hydrophobicity of the forming adsorbed layer. At moderate pH, competition of two types of interaction occurs. In the case of polyelectrolyte, time of adsorption (flocculating concentration) decreases because of far-range electrostatic attraction. Formation of a soluble polymer-colloid complex in the form of small loose (reversible) flocs with variable composition provides for the electrostatic attachment of macromolecules near the particle surface, thus promoting the formation of a short-range coordination bond. The qualitative mode of the selective interaction of the colloidal particles with ionic macromolecules having chemisorbable groups was suggested.