Cellular networks of colloids via the demixing and remixing of binary liquids
Phase separation provides an intriguing and novel route towards the fabrication of colloid-stabilized emulsions, as quenching of a binary liquid into the demixed regime can cause nucleation and growth of fluid droplets. In our experiments, we typically employ silica nanoparticles in mixtures of methanol and hexane, characterizing the system in 3D and in real time using confocal microscopy.
Heating up these emulsions, back into the single-fluid phase, we have observed coarsening, culminating in the formation of cellular, nanoparticle networks. These networks appear just before the liquids remix and are therefore short-lived, though we have been able to 'stabilize' them for 15 to 30 minutes by quenching to a temperature close to the binodal. Network formation and morphology depend on the surface chemistry of the particles, the colloid volume fraction and the quench rate.
Apart from being a rather curious phenomenon from an academic point of view, similar networks may have applications in materials science, e.g. as templates for metal foams, in bone tissue engineering, etc. However, it is not yet clear what the underlying mechanism for network formation is, so any suggestions are more than welcome.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..