The role of sample height in the stacking diagram of colloidal mixtures under gravity

Abstract

Bulk phase separation is responsible for the occurrence of stacks of different layers in sedimentation of colloidal mixtures. A recently proposed theory (de las Heras and Schmidt 2013 Soft Matter 9 8636) establishes a unique connection between the bulk phase behaviour and sedimentation-diffusion-equilibrium. The theory constructs a stacking diagram of all possible sequences of stacks under gravity in the limit of very high (infinite) sample heights. Here, we study the stacking diagrams of colloidal mixtures at finite sample height, h. We demonstrate that h plays a vital role in sedimentation-diffusion-equilibrium of colloidal mixtures. The region of the stacking diagram occupied by a given sequence of stacks depends on h. Hence, two samples with different heights but identical colloidal concentrations can develop different stacking sequences. In addition, the stacking diagrams for different heights can be qualitatively different since some stacking sequences occur only in a given interval of sample heights. We use the theory to investigate the stacking diagrams of both model bulk systems and mixtures of patchy particles that differ either by the number or by the types of patches.

Gravity-induced phase phenomena in plate-rod colloidal mixtures

“…From the bulk phase diagram we construct the stacking diagram by finding the boundaries between two stacking sequences in the stacking diagram. There exist three types of boundaries formed by three sets of special sedimentation paths 41 , Fig. 1 Model.…”

“…As discussed above, it is useful to group the stacking sequences in a finite height stacking diagram 41 . Figure 4 shows the stacking diagrams for samples with heights h = 5 mm (c,d) and 18 mm (e,f) in the plane of average chemical potentials (c,e) and average packing fractions (d,f) along the path.…”

“…The stacking sequences are grouped in a stacking diagram, which is the analog of the bulk phase diagram for systems subject to gravity. So far, the stacking diagrams have been used to theoretically study sedimentation of model colloidal mixtures 21,[40][41][42] .…”

Dynamics of network fluids

“…The idea is to control the branching rate, since two-patch colloidal particles only form chains and colloidal particles with more patches promote branching. A study based on local density approximation of multilayer stacking of this type of binary mixtures in a gravitational field has shown stacking diagrams with different stacking sequences [72]. The authors studied the effect of the finite thickness of the stacked film on the occurrence of stacks of different layers during sedimentation.…”

Percolation of functionalized colloids on patterned substrates

“…The percolation is only recovered for very high packing fractions. Previous studies of functionalized colloidal particles have reported also reentrant phenomena driven by, e.g., gravitational fields [33,34], competition between different energy scales [35][36][37], and patches activated by temperature [38].…”