Based on the theory of free volume, it is established that the Kirkwood-Alder transitions in concentrated model systems of noninteracting hard spheres are caused by external forces. Analysis shows that when describing order-disorder transitions in real colloidal systems the interaction of particles can be ignored if the potential energy of the particles in the forming dense phase (|uk|) is lower than (5–10)kT. Two types of transition into a dense, including an ordered, state of particles are possible in real suspensions: 1) transitions caused by strong interparticle attraction, with |uk| ≥ 40kT (coagulation), which are possible even in diluted suspensions, and 2) transitions under the effect of external forces (Alder transitions) in concentrated suspensions of weakly interacting colloidal particles, with |uk| < (5–10)kT (formation of regular colloidal structures (RCS)). Formation of monodisperse spheres of silica (MSS) in fine suspensions of its particles is probably a first-type transition. Production of the RCS of precious opals from MSS is a second-type transition; this process should include the stage of suspension consolidation. In nature, such RCS are necessary for the formation of the consolidated regular structures of precious opals.

First Page Preview

First page of THERMODYNAMIC ANALYSIS OF FORMATION OF CRYSTAL -LIKE PRECIOUS -OPAL STRUCTURES
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.