Synthetic boundary crystallization ultracentrifugation:: a new method for the observation of nucleation and growth of inorganic colloids and the determination of stabilizer efficiencies

Synthetic boundary cells were applied for carrying out inorganic nucleation reactions inside the analytical ultracentrifuge. A reactant containing solution was layered onto a more dense solution containing the other reactant when the centrifuge was speeded up so that a very sharp and defined reaction boundary was formed. Due to the acting high centrifugal field, even the smallest colloids formed sediment out of the reaction boundary so that their growth is stopped. Simultaneously, the particle size distribution can be determined via the experimentally accessible sedimentation coefficients reflecting the growth process of the colloidal system. Thus, the whole method makes use of the stopped growth once the particles leave the sharp reaction boundary paired with the observation of their movement in the centrifugal field. This 'synthetic boundary crystallization method' is applied to thiol stabilized quantum size cadmium sulfide particles as a model system demonstrating the accessible information. The observed differences of the CdS particle size distributions induced already by chemically quite similar stabilizer molecules not only demonstrate the high resolution of the method, but furthermore suggest it as a fast measuring method for the determination of stabilizer efficiencies and of the impact of modifiers on crystallization at the stage of the primary nuclei. (C) 2000 Elsevier Science B.V. All rights reserved.