화학공학소재연구정보센터
Journal of Colloid and Interface Science, Vol.228, No.1, 151-156, 2000
Kinetic analyses of colloidal crystallization in a wide range of sphere concentrations as studied by reflection spectroscopy
The nucleation and growth rates in the colloidal crystallization of silica spheres (103 nm in diameter) from 0.006 to 0.04 in volume fraction (phi) have been measured by reflection spectroscopy. Kinetics of the crystallization has been discussed in a wide sphere concentration range (from phi = 0.0005 to phi = 0.04) using the data of this work and the previous work (110 nm in diameter) in exhaustively deionized aqueous suspensions. The induction period for nucleation decreases sharply as the sphere concentration increases. The nucleation rate increases substantially from 1 x 10(-3) to 1 x 10(7) mm(-3) s(-1) when phi increases from 0.0005 to 0.04. The crystal growth process consists of the fast growing step toward metastable crystals (rate nu(1)) and slow growth accompanied with the reorientation toward stable ones (rate nu(2)). The nu(1) values increase first from 5 to 20 mu m/s and then turn back to 5 mu m/s after passing a maximum. nu(1) above phi = 0.01 remains at 5 mu m/s and is insensitive to sphere concentration, The slow step is observed in the high-sphere concentrations only, and nu(2) decreases sharply from 3 mu m/s to 0.7 nm/s when sphere concentration increases from 0.004 to 0.04 in volume fraction. Importance of the electrostatic intersphere repulsion by overlapping of the electrical double layers and the cooperative and synchronized fluctuation of colloidal spheres in the crystallization processes are supported strongly.