Physics: Prof. dr. M. Dijkstra, Univ. of Utrecht: Colloidal Self-asesmbly: Predicting and designing new Structures
|15 January 2009||FWN-Building 5111.0080, Nijenborgh 4, 9747 AG, Groningen|
|Speaker:||Physics: Prof. dr. Marjolein Dijkstra|
|Affiliation:||University of Utrecht|
|Title:||Colloidal Self-asesmbly: Predicting and designing new Structures|
Colloidal suspensions are complex fluids that consist of mesoscopic particles moving around in a solvent. The addition of other components such as salt ions or added polymers enables us to tune the effective interactions between the colloids.
In this talk, we show how one can exploit this picture of colloids as extremely tunable "building blocks" to obtain new phases and new structures which may lead to "advanced functional materials", e.g., e-ink displays, photonic bandgap structures, and electrorheological fluids. More specifically, we show that binary hard-sphere mixtures can either give rise to a broad fluid-solid transition or can organize spontaneously into superlattice structures depending on the precise size ratio of the two species. To this end, we develop genetic algorithms to predict the possible binary crystal structures. In addition, mixtures of oppositely charged colloids display a remarkably rich variety of crystal structures as the crystal structure is not dictated by the charge neutrality condition as in the case of ionic crystals. The resulting phase diagram of oppositely charged colloids displays colloidal analogs of simple-salt structures, colloidal counterparts of the doped fullerene structures, but also novel structures with large-small stoichiometries 1:6 and 1:8 that do not have an atomic or molecular analog. In addition, we study the crystal nucleation of oppositely charged colloids. Two different crystal structures compete in the thermodynamic conditions under study. We find that the crystal phase that nucleates is metastable and, more surprisingly, its nucleation free energy barrier is not the lowest one. This implies that, during nucleation, there is insufficient time for pre-critical nuclei to relax to their lowest free-energy structure. We also study nucleation of rodlike particles and the effect of non-adsorbing polymer on the nucleation process. Finally, we show that many new phases can be manipulated by external fields, e.g., an electric field stabilizes the hexagonal-close-packed, body-centered-orthorhombic, and body-centered-tetragonal phase, while triangular, square, buckling, and prism phases are found in confined hard spheres.
|Last modified:||12 September 2014 11.21 a.m.|