Colloidal Gels Assembled via a Temporary Interfacial Scaffold

The liquid-liquid phase separation of a binary solvent can be arrested by colloidal particles trapped at the interface [K. Stratford et al., Science 309, 2198 (2005)]. We show experimentally that the colloidal network so formed can remain stable after fully remixing the liquids, creating a new type of gel in which colloids in a single-phase solvent have locally planar coordination. We argue that this structure is likely maintained by primary-minimum Derjaguin-Landau-Verweg-Overbeek bonding of our charged colloids, created under strong compression by capillary forces. We present simulation evidence that the combination of a short-ranged attraction with a repulsive barrier can strongly stabilize such locally planar gels.

Figure 1

Confocal microscopy images of critical-composition water [dark grey (black)]-lutidine [grey (red)] mixtures containing silica particles [bright grey (green)]. Scale bar is $100\mu \mathrm{m}$. The upper images were taken with the samples at $40°\mathrm{C}$ and the lower images were taken after cooling into the single-fluid phase. Rhodamine B dye (red) shows the presence of a lutidine-rich phase. In (a) the bijel was cooled sooner than in (b), where the colloidal gel remained stable after the liquid phases had remixed. Further particle details are given in [14]. See 24 for movies of both experiments. Inset to (b): a section from the starting bijel colloidal network used in our computer simulations.

Figure 2

(a) A square-well attractive interaction (SRA). (b) A square-well attraction combined with a ramp repulsion for longer distances (SRA-LRR). (c) Sketch of DLVO potential [18].

Figure 3

Mean square displacement at two different times for SRA and SRA-LRR interactions. Particles interacting via SRA-LRR barely move, their displacement being clearly subdiffusive.

Figure 4

A slab of the initial configuration is compared to those obtained after simulating 200 $t$ for both SRA-LRR and SRA interactions and different attractive ranges $\lambda$.