Nanoseminar 5 November - dr. Chris Kennedy (TUe)

Speaker: dr. Chris Kennedy (TUe - Applied Physics, Soft Matter and Biological Physics) 

Title: Single particle diffusiophoresis and cubes with critical Casimir attractions

Abstract: In the first part of this presentation, I will discuss diffusiophoresis. This motion of particles due to solute gradients has long been in the shadow of its more experimentally convenient sibling: electrophoresis. However, modern microfluidics has provided a method to maintain stable concentration gradients and the relevance of diffusiophoresis to active matter has provided a motivation to better understand this phenomenon. Previously, ensemble measurements of changing particle concentration demonstrated controlled transport using salt gradients [1]. We extended this work with measurements of single particles, allowing a more detailed test of the theory describing diffusiophoresis [2].

In the second part, I will share the results of recent work in Eindhoven. We are investigating the assembly of attractive rounded cubelike particles. These silica ‘superballs’ have been studied with depletion attractions which revealed phases with both square and rhombic symmetry, depending on depletant size [3]. We induced attractions using a different mechanism: the temperature dependent critical Casimir force. Using confocal microscopy, we observed the assembly dynamics of clusters with square symmetry, which transition to a rhombic phase at higher attraction strength. These first results show promise of revealing a piece of the larger puzzle of relating assembled structures to the building block shape and interactions.

1. Abécassis et al. Boosting migration of large particles by solute contrasts. Nature Mater 7, 785 (2008). 10.1038/nmat2254
2. Kennedy, Chris PhD thesis: ch. 5. UU (2020) 10.33540/132
3. Rossi et al. Shape-sensitive crystallization in colloidal superball fluids. PNAS 112, 5286 (2015). 10.1073/pnas.1415467112