Kinetic Study on the Colloidal Crystallization of Silica Spheres in the Highly Diluted and Exhaustively Deionized Suspensions as Studied by Light-Scattering and Reflection Spectroscopy

✍ Scribed by Tsuneo Okubo; Shinji Okada; Akira Tsuchida

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 237 KB
• Volume: 189
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1997.4831

✦ Synopsis

aqueous suspensions ( 14 -20 ) and concentrated suspen-Static (SLS) and dynamic light-scattering (DLS) measurements sions in the refractive index matched organic solvents and reflection spectroscopy are made for the kinetic analyses of the ( 21 -29 ) .

growing processes of colloidal crystals of silica spheres (103 and

When we study the colloidal crystals in diluted aqueous 110 nm in diameter) in highly diluted and exhaustively deionized suspensions, the suspensions, first of all, must be deionaqueous suspensions. Changes in the SLS curves demonstrate that ized with ion-exchange resins as completely as possible.

there exists an induction period in the nucleation process, which is Deionization of the colloidal suspensions with the resins prolonged with decreasing sphere concentration. Induction periods is not made so fast and effectively. In our experiences, it observed from DLS measurements are from 1 to 21 min, and also increase as sphere concentration decreases. The diffusion coeffi-took more than 3 or 4 weeks before the complete deionizacients of colloidal spheres in the super-saturated liquids and crystaltion state was achieved. A convenient criterion for knowlike structures are estimated to be 1 1 10 012 and 5-10 1 10 012 m 2 / ing the degree of deionization is to check the critical s, respectively, which are smaller and larger than the diffusion sphere concentration of melting of crystal, f c , in volume coefficient of the independent sphere evaluated using the Stokesfraction. When the colloidal suspensions are deionized in Einstein equation, 4.36 1 10 012 m 2 /s. Nucleation rates are 5.6 1 a usual way with the ion-exchange resins for several hours 10 04 to 3.2 1 10 03 mm 03 s 01 at f Å 0.0006 to 0.001 from the in the observation cell, for example, f c values are in the DLS and reflection spectroscopy. The crystal growing process is range from 0.001 to 0.002 ( 30 -32 ) . On the other hand, beautifully explained by the classical diffusion theory of crystallizawhen the sample suspensions are deionized with resins tion, though the restricted diffusion of the reacting spheres like as most carefully more than 3 weeks, the f c value becomes the fused metal systems should be taken into account. Crystal growth rates range from 2.9 to 20.7 mm/s and increase substantially much lower in the range from 0.0001 to 0.0003 as we as the sphere concentration increases. The importance of the electrohave reported recently ( 33 ) .

static intersphere repulsion through the electrical double layers and

Recently we have measured the static ( SLS ) and dythe cooperative fluctuation of colloidal spheres in the crystallization namic light-scattering ( DLS ) of the colloidal crystals in processes is supported strongly. ᭧ 1997 Academic Press the exhaustively deionized and highly diluted aqueous Key Words: colloidal crystals; crystal growth kinetics; light scatsuspensions ( 34 -37 ) . In these experiments the diffusion tering; reflection spectrum. coefficients of colloidal crystals at the scattering vectors at the peaks in the SLS curves were much larger than those of the corresponding colloidal liquids. This observation