Dynamic Scaling of Colloidal Gel Formation at Intermediate Concentrations

Abstract

We have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scattering, x-ray photon correlation spectroscopy, and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically determined gel temperature, T_{gel}, was characterized via the slowdown of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth (ΔT=T_{quench}-T_{gel}), wave vector, and formation time t_{f}. We find the wave-vector-dependent dynamics, microstructure, and rheology at a particular ΔT and t_{f} map to those at other ΔTs and t_{f}s via an effective scaling temperature, T_{s}. A single T_{s} applies to a broad range of ΔT and t_{f} but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of ΔT than expected from the attraction strength between colloids. We interpret this strong temperature dependence in terms of cooperative bonding required to form stable gels via energetically favored, local structures.

Enhanced gel formation in binary mixtures of nanocolloids with short-range attraction

“…[37][38][39][40][41][42] Recent work by our group and others has further investigated the temporal evolution of the rheology and particle-scale dynamics, using a combination of rheometry and XPCS, to identify quantitative relationships between the macroscopic mechanical behavior and microscopic motions in the gels. [43][44][45] Here, we use this set of tools in conjunction with simulations to explore gel formation in suspensions of bidisperse mixtures of these colloids. The mixtures contained colloids of radii R L ≈ 16 nm and R S ≈ 8 nm (i.e., κ ≈ 2), with a size polydispersity of approximately 10%.…”

Dynamics of soft nanoparticle suspensions at hard X-ray FEL sources below the radiation-damage threshold

“…For soft-matter systems XPCS is used whenever the application of light-scattering methods is challenged. This includes, for example, glass formation and gelation of dense polymeric and colloidal systems (Guo et al, 2012;Kwaśniewski et al, 2014;Conrad et al, 2015;Zhang et al, 2017) or soft matter under shear (Leheny et al, 2015).…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…Colloidal systems also turn into gels and glasses depending on the concentration and interactions, and SAXS has been used to probe the underlying long-range and short-range interactions [27,29,30]. A similar approach has been employed to unravel the combined effects of ionic strength, temperature, and pressure on protein-protein interaction potential and the phase behavior in dense lysozyme solutions [31].…”

“…The time scale accessible by XPCS is determined by the scattering power of the sample, available coherent photon flux, and detector capabilities. The main applications of XPCS have been to probe the dynamics of colloids, especially those that are turbid in visible light [106] and slow dynamics in arrested systems such as gels [29] and glasses [27]. Faster dynamics at a given q can be accessed with a point detector [106]; however, an additional limitation is the onset of radiation damage with longer exposure of the sample to the X-ray beam.…”