Small-angle static light scattering of concentrated silica suspensions during in situ destabilization

Concentration effects on irreversible colloid cluster aggregation and gelation of silica dispersions

“…To remedy this drawback, uniform distribution of salt can be realized through internal generation of electrolyte obtained from a chemical reaction in the solvent. This has been used in several studies of concentrated systems with a great deal of success [5,24,25,29,30,45,46]. A second complication arises now since the ionic strength increases with time and pinpointing the ionic strength at any given time thus requires calibration of the reaction.…”

“…Particle aggregation and gelation in concentrated systems have been studied very effectively with dynamic light scattering techniques in the past, revealing non-ergodic dynamics close to gelation [24,28,29]. The analysis of dynamic light scattering data on aggregating samples is complicated by multiple scattering; a number of techniques have been developed to suppress multiple scattering [51][52][53][54].…”

“…In dilute suspensions of irreversibly aggregating colloids it is well established that fractal concepts capture this interplay [8][9][10][11] particularly the subsuming of the details of the colloidal interactions by the aggregation kinetics resulting in two universal limiting regimes, diffusion-limited [12][13][14][15] and reaction-limited [16][17][18] cluster aggregation. While further characterization and modeling of aggregation kinetics is being pursued [19][20][21][22][23], focus has also more recently been directed at concentrated suspensions [24][25][26][27][28][29][30], for which a similarly firm connection between structure, kinetics, and properties is lacking.…”

“…Aggregation generally terminates in gelation as opposed to phase separation, at least phase separation in the conventional sense [31], whereby the system assumes solid-like character with a diverging viscosity [32], a finite yield stress [33,34], and a low-frequency elastic modulus [25,27,29,35]. Structurally, it is characterized by the formation of a macroscopic, spacefilling particle/cluster network [2,[36][37][38].…”

“…The chemical products reduce the repulsive, stabilizing forces among particles either by shifting the pH towards the isoelectric point or by raising the ionic strength. In the former case, the surface charge is gradually neutralized and in the latter it becomes increasingly screened [5,29]. Here we make use of the ionic strength increase that results from the urease-catalyzed hydrolysis of urea.…”