Microdynamics and arrest of coarsening during spinodal decomposition in thermoreversible colloidal gels

Abstract

Coarsening and kinetic arrest of colloidal systems undergoing spinodal decomposition (SD) is a conserved motif for forming hierarchical, bicontinuous structures. Although the thermodynamic origins of SD in colloids are widely known, the microstructural processes responsible for its coarsening and associated dynamics en route to arrest remain elusive. To better elucidate the underlying large-scale microdynamical processes, we study a colloidal system with moderate-range attractions which displays characteristic features of arrested SD, and study its dynamics during coarsening through a combination of differential dynamic microscopy and real-space tracking. Using these recently developed imaging techniques, we reveal directly that the coarsening arises from collective dynamics of dense domains, which undergo slow, intermittent, and ballistic motion. These collective motions indicate interfacial effects to be the driving force of coarsening. The nature of the gelation enables control of the arrested length scale of coarsening by the depths of quenching into the spinodal regime, which we demonstrate to provide an effective means to control the elasticity of colloidal gels.

Differential dynamic microscopy microrheology of soft materials: A tracking-free determination of the frequency-dependent loss and storage moduli

“…These data are treated via an image processing algorithm [22] or equivalent versions of it [23] that combines image differences and spatial Fourier transformations to obtain as a result the intermediate scattering function f (q,t) that is typically probed in DLS experiments as a function of the scattering wave vector q and time t [24]. Since its introduction, DDM has been profitably used and also extended by several groups [25][26][27][28][29][30][31][32][33][34] for a variety of applications [35]. In particular, DDM has been recently proven to be an effective tool to measure also the rotational dynamics of anisotropic colloidal particles in solution.…”

Dynamical scaling for underdamped strain order parameters quenched below first-order phase transitions

“…4(c) . A similar "coarsening arrest" has been considered elsewhere 22 . We here suggest a toy model, to provide some understanding.…”

“…The exponent takes on sequential values such as α = 2/3, 1/2 over time windows, whose widths depend on the quench temperature T . For deep quenches, there is an exponent α = 1/3, and a final α 0 flattening to a constant, analogous to 'coarsening arrest' 22 . These 2D results are found to persist, for 3D.…”

Equilibration and Aging of Liquids of Non-Spherically Interacting Particles

“…As we know, quenching a liquid from supercritical temperatures to a state point inside its gas-liquid spinodal region, normally leads to the full phase separation through a process that starts with the amplification of spatial density fluctuations of certain specific wave-lengths [28][29][30]. Under some conditions, however, this process may be interrupted when the denser phase solidifies as an amorphous sponge-like non-equilibrium bicontinuous structure [31][32][33][34][35], typical of physical gels [36]. This process is referred to as arrested spinodal decomposition, and has been observed in many colloidal systems, including colloidpolymer mixtures [31], mixtures of equally-sized oppositely-charged colloids [32], lysozyme protein solutions [33], mono-and bi-component suspensions of colloids with DNA-mediated attractions [34], and thermosensitive nanoemulsions [35].…”

“…Under some conditions, however, this process may be interrupted when the denser phase solidifies as an amorphous sponge-like non-equilibrium bicontinuous structure [31][32][33][34][35], typical of physical gels [36]. This process is referred to as arrested spinodal decomposition, and has been observed in many colloidal systems, including colloidpolymer mixtures [31], mixtures of equally-sized oppositely-charged colloids [32], lysozyme protein solutions [33], mono-and bi-component suspensions of colloids with DNA-mediated attractions [34], and thermosensitive nanoemulsions [35]. From the theoretical side, it was not clear how to extend the classical theory of spinodal decomposition [28][29][30] to include the possibility of dynamic arrest, or how to incorporate the characteristic non-stationarity of spinodal decomposition, in existing theories of glassy behavior [40].…”