Phase separation dynamics in colloid–polymer mixtures: the effect of interaction range

Abstract

Colloid-polymer mixtures may undergo either fluid-fluid phase separation or gelation. This depends on the depth of the quench (polymer concentration) and polymer-colloid size ratio. We present a real-space study of dynamics in phase separating colloid-polymer mixtures with medium-to long-range attractions (polymercolloid size ratio q R = 0.45 − 0.89), with the aim of understanding the mechanism of gelation as the range of the attraction is changed. In contrast to previous studies of short-range attractive systems, where gelation occurs shortly after crossing the equilibrium phase boundary, we find a substantial region of fluid-fluid phase separation. On deeper quenches the system undergoes a continuous crossover to gel formation. We identify two regimes, 'classical' phase separation, where single particle relaxation is faster than the dynamics of phase separation, and 'viscoelastic' phase separation, where demixing is slowed down appreciably due to slow dynamics in the colloid-rich phase. Particles at the surface of the strands of the network exhibit significantly greater mobility than those buried inside the gel strand which presents a method for coarsening. arXiv:1209.3973v1 [cond-mat.soft]

Kinetics of liquid–liquid phase separation in protein solutions exhibiting LCST phase behavior studied by time-resolved USAXS and VSANS

“…This later stage behavior could be due to migration and coalescence of minority phase droplets through a glassy phase 60 or rearrangements of the majority phase due to mechanical stress relaxation. 57,62 Olais-Govea et al have recently proposed a non-equilibrium theory of arrested spinodal decomposition, 63 which reproduces the main experimental observations in colloid and protein systems. 9,10,12,64 In their framework, the dynamic arrest of a solution undergoing LLPS can lead to three scenarios, depending on the quench depth.…”

The role of quench rate in colloidal gels

“…Systems with short-ranged attractive interactions (up to around 10% of the particle size) are well known to undergo gelation [1][2][3]. In the case of longer-ranged attractions in which the liquid state is stable, shallow quenches below the gas-liquid spinodal lead to complete phase separation [6,7]. Systems with short-ranged attractions and long-ranged repulsions can also exhibit similar behaviour [1,[8][9][10].…”

Colloidal behavior of nanoemulsions: Interactions, structure, and rheology

“…[120] This has limited the study of gels formed by arrested phase separation mostly to their characterization in the arrested state, with very few studies made during their formation. [133] The thermoresponsive bridging nanoemulsion system of Helgeson and co-workers has thus emerged as a model system for studying the juxtaposition of phase separation and attractive glass formation as a route to colloidal gelation, again owing to the ability to carefully control the path through the colloidal phase diagram to the gelled state. [29,32,84,89] To illustrate the behavior, the qualitative features of a phase diagram obtained by modeling the bridging interactions as a temperature-responsive square well attraction [84] is reproduced in Figure 1.…”