Time–connectivity superposition and the gel/glass duality of weak colloidal gels

Abstract

Colloidal gels result from the aggregation of Brownian particles suspended in a solvent. Gelation is induced by attractive interactions between individual particles that drive the formation of clusters, which in turn aggregate to form a space-spanning structure. We study this process in aluminosilicate colloidal gels through time-resolved structural and mechanical spectroscopy. Using the time–connectivity superposition principle a series of rapidly acquired linear viscoelastic spectra, measured throughout the gelation process by applying an exponential chirp protocol, are rescaled onto a universal master curve that spans over eight orders of magnitude in reduced frequency. This analysis reveals that the underlying relaxation time spectrum of the colloidal gel is symmetric in time with power-law tails characterized by a single exponent that is set at the gel point. The microstructural mechanical network has a dual character; at short length scales and fast times it appears glassy, whereas at longer times and larger scales it is gel-like. These results can be captured by a simple three-parameter constitutive model and demonstrate that the microstructure of a mature colloidal gel bears the residual skeleton of the original sample-spanning network that is created at the gel point. Our conclusions are confirmed by applying the same technique to another well-known colloidal gel system composed of attractive silica nanoparticles. The results illustrate the power of the time–connectivity superposition principle for this class of soft glassy materials and provide a compact description for the dichotomous viscoelastic nature of weak colloidal gels.

Incorporating Rheological Nonlinearity into Fractional Calculus Descriptions of Fractal Matter and Multi-Scale Complex Fluids

“…Secondly, in the Fractional Maxwell Gel (FMG) limit, exponent β is constrained to be zero (β = 0). This FMG model accurately captures the predominantly elastic behavior of viscoelastic materials beyond the gel point [52], and the quasi-property G characterizes the plateau modulus of the gel (G (ω → ∞) = G (Pa)). The three-parameter FMG model (G, α and V) mechanically translates to a series combination of a spring and a springpot as shown in Figure 1c (i).…”

Condensation and growth of amorphous aluminosilicate nanoparticles via an aggregation process

“…As previously described, our models were built upon the experimental data in terms of chemical composition, the density of the solutions, and NMR measurements, Dupuis et and Na/Al=10.92. The addition of aluminates monomers to the silicate solution initiates the polycondensation reactions to form aluminosilicate entities that grow and interact each other to form a gel [25]. Figure 4 shows the scattering intensity of the gel in SAXS and WAXS configuration.…”

“…The mixed solution has final concentrations of [Si] = 1.125 mol.L −1 , [Na] = 1.31 mol.L −1 , [Al] = 0.12 mol.L −1 . After the mixing, decondensation of silicate chains due to the presence of sodium hydroxide [21] and condensation of aluminosilicate species happen simultaneously [25]. Simulations are used to distinguish different mechanisms of the aluminosilicate formation, at the atomic scale, that can not be observed directly experimentally because of the involved time-scale that are not compatible with experimental devices.…”

Interpenetration of fractal clusters drives elasticity in colloidal gels formed upon flow cessation

“…The intensity scattered by the carbon black is fitted in log scale using a modified Beaucage model [51,52,85], Fig. 13:…”