Kinetic behaviour of the system composed of nanosized gold particles and very-high-molecular-weight polyacrylamide

We have investigated a process of aggregation of large macromolecules of polyacrylamide (PAAm) and gold particles of nanometre size suspended in aqueous medium. In the presence of PAAm, the resistance of gold particles to the coagulating action of electrolytes increases considerably. A study of the salt-induced coagulation of gold particles proceeding in the presence of PAAm has shown that the initial aggregation of particles and macromolecules begins as a rapid process, which slows down after some time. In the incipient stage, a single macromolecule can attach a number of particles forming a multiplet. If there are free particles left in the system, a subsequent process of particle-multiplet association occurs, as observed in dynamic light scattering experiments. A considerable increase in the relaxation time of the process was interpreted as a result of the multiplet reconformation needed for the attachment of an additional particle. The changes in the multiplet properties were followed spectroscopically. The long-term changes in light extinction spectra were attributed to the rearrangement of particles within multiplets. The behaviour of the system is affected by the presence of simple electrolytes, which reduce the multiplet stability.