Time-Dependent Strength of Colloidal Gels

Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.

Figure 1

Dynamic structure factors at $q=3771{\mathrm{cm}}^{-1}$; raw data at 12 (solid line), 18 (dashed line), 40 (dash-dotted line), 55 (■), 69 (●), and 93 h (▲) since initialization and corrected for external temperature fluctuations at 55 (□), 69 (○), and 93 h (△). Inset: Static light scattering between 1 and 65 h after initialization. No changes are observed after $\sim 15\mathrm{h}$.

Figure 2

Linear storage (filled symbols) and loss (open symbols) moduli for different volume fractions at strain amplitude $\gamma =5\times {10}^{-3}$.

Figure 3

Growth of the linear storage modulus $G^{\prime }$ with time for different volume fractions. Scale factors $\beta$ used to shift $G^{\prime }$ onto a single master curve (inset).

Figure 4

Schematic of two sintering spheres.