Confinement induced assembly of anisotropic particles: patchy colloids and water molecules

Date: 26 September 2016

Venue: UAntwerpen, Campus Middelheim, G0.10 - Middelheimlaa 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim)

Time: 4:00 PM

Organization / co-organization: Department of Physics

PhD candidate: Mario SOBRINO FERNÁNDEZ

Principal investigator: F. Peeters, M. Neek-Amal, V. Misko

Short description: PhD defence Mario Sobrino Fernàndez - Faculty of Science, Department of Physics



Abstract

We focus on questions concerning the effect of confinement on the ability of individual constituents to form large scale aggregates. The research is divided into two parts. In the first, the structural and dynamical properties of patchy colloids is explored. The second part is devoted to the formation of ice monolayers when water is confined between two graphene layers.

Colloidal systems consist of mesoscopic particles that can be regarded as large atoms, although they can be studied using physics with less consideration of their chemical signatures at the microscopic level. We studied the dynamics of Janus spheres consisting of a hydrophobic and charged hemisphere. Using the interplay of these competing interactions, the morphology of these particles is studied. A variety of ordered membranes are found consisting of single and multiple chain configurations with different particle orientations which are summarized in a phase diagram. The interplay of the competing interactions between two hemispheres can result in a self-assembly of helical superstructures whose helicity can be controlled by altering the pH concentration of the solution in which the spheres are placed.

When water is confined in hydrophobic pores, the hydrogen-bond network is forced to terminate at these surfaces. As a result, the entire hydrogen-bond network is frustrated, causing its properties to be altered. In a recent experiment, a TEM microscopy image was reported of water locked between two graphene sheets. Their observation showed that such nanoconfined water forms a cubic ice crystal structure. Using the reactive bond order potential ReaxFF the formation of ice crystals between graphene layers is explored. External parameters were chosen in order to replicate the experimental setup. We find that nonpolar flat layers of ice can nucleate between the graphene layers with a crystal structure having a unit cell consisting of a square-rhombic tiling. Subsequent square-ice layers are found to be shifted in-plane over a fraction of the lattice constant.



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