Time-Resolved Dynamic Light Scattering Study on the Dynamics of Silica Gels during Gelation Process

Abstract

The dynamics and structure have been compared for two types of silica gels prepared from tetramethoxysilane in dimethylformamide under acidic and basic conditions. An in-situ time-resolved dynamic light scattering (TRDLS) technique was employed to investigate the changes of the dynamics during gelation process. In both cases, a clear power-law behavior in the time-intensity correlation function, g (2) (τ) -1 ∼ τ n-1 , was observed at the gelation threshold, from which the critical exponent of viscoelasticity, n, was evaluated. The gelation of the acid system was slower, and the gelation time was a weak decreasing function of the initial monomer concentration, C. The resultant gel was found to be made of long polysiloxane chains slightly connected with each other, which was characterized by n ≈ 0.5. On the other hand, the gelation time of silica gels prepared with a basic catalyst was strongly dependent on C. The evaluated value n ≈ 0.73 indicates the presence of highly branched clusters with short strands. It is demonstrated that the TRDLS technique is a powerful tool to investigate gelation process of silica from both dynamic and structural points of view.

Dynamic Light-Scattering Study of Aggregating and Gelling Colloidal Disks

“…DLS experiments show a remarkably similar behavior of g 2 (t) for very different gel-forming systems such as silica (8,9), Laponite (10), polyurethane (11), polysaccharides (12), PMMA (13), and globular proteins (14). Usually, a fast decay is observed followed by a stretched exponential decay sometimes preceded by power law decay.…”

The slow relaxation mode: from solutions to gel networks

“…During the sol-gel transition, the bimode distribution is clearly preserved, although the relative contribution of the fast relaxation decreases. Shibayama and colleagues 145 also reported that the fast mode remained in the formation of silica gels. Another interesting point is that the position of the peak related to the fast relaxation nearly remains during the sol-gel transition, different from other gelling systems.…”

Universality and Specificity of Polymer Gels Viewed by Scattering Methods

“…12). vestigated so far: (a) chemical gels, (b) hybrid gels consisting of inorganic silica and organic polymer gels, 96,97 and polymerclay nanocomposite gel, 98 ). It is essential to have (1) an increase in scattering intensity and (2) power-law behavior at gelation threshold, t gel .…”