Colloid-Polymer Mixtures at Triple Coexistence: Kinetic Maps from Free-Energy Landscapes

Abstract

We have studied the kinetics of phase separation in a colloid-polymer mixture. The evolution of initially homogeneous samples as they separate into coexisting colloidal gas, liquid, and crystal phases was investigated by time-lapse video recording. Distinct kinetic regimes were found, the existence and character of which are interpreted in terms of the "free energy landscape" of the system.

Can Polymer Coils Be Modeled as “Soft Colloids”?

“…For such systems, the soft colloid model may now be used in large-scale simulations or fluid integral equations of polymers in complex geometries, such as the structure [23], phase behavior [1], interactions [2], and metastability [3] of colloid-polymer mixtures, which cannot be achieved with the detailed model of nonintersecting polymer chains. …”

“…The mapping opens up the possibility of large-scale simulations of polymer solutions in complex geometries. A statistical description of polymer solutions in complex geometries, such as the colloid-polymer mixtures which have recently received much experimental attention [1][2][3], generally relies on a nanometer scale segment representation of the polymer coils, a computationally very demanding task except in the special case of ideal (nonintersecting) polymers obeying Gaussian statistics [4]. This obviously follows from the fact that, although the colloidal particles may reasonably be modeled by hard impenetrable spheres or other complex shapes lacking internal structure, each polymer coil involves L segments which must satisfy a nonintersection constraint.…”

Novel zone formation due to interplay between sedimentation and phase ordering

“…Here the interplay between sedimentation and the equilibrium phase diagram (see fig. 1(a) [5]) and phase ordering leads to fascinating unexpected kinetic pathways. We emphasise that C+C+P is not merely a complication of C+P, but a minimal system exhibiting both phase condensation, driven by depletion, and frustration against crystallisation due to polydispersity.…”

“…In a suspension of a finite concentration, the kinetics of sedimentation are strongly influenced by hydrodynamic interactions between particles [2,3], and direct attractive interactions between the sedimenting particles can have a drastic effect and even qualitatively alter the simple picture above [4]. For example, in a colloid-polymer mixture (C+P), complex couplings between sedimentation and the polymer concentration come into play [5]. The polymer chemical potential drives the depletion attraction between the colloids, yet the polymer free volume is itself coupled to a state point of the system [6].…”

The effect of size ratio on the sphere structure factor in colloidal sphere-plate mixtures

“…A further phase is observed if q is increased to 0.4, giving a triple gas-liquid-solid coexistence. 17,20 The maximum depth and range of the depletion attraction are controlled by the concentration and size of the depletant agent, respectively. 12,21,22 Changing these factors will affect the phase behaviour of the colloidal mixtures and the interparticle structure.…”