Phase separation and self-assembly of colloidal dimers with tunable attractive strength: from symmetrical square-wells to Janus dumbbells

We numerically investigate colloidal dimers with asymmetric interaction strengths to study how the interplay between molecular geometry, excluded volume effects and attractive forces determines the overall phase behavior of such systems. Specifically, our model is constituted by two rigidly-connecte...

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Bibliographic Details
Published in:Soft matter 2014-08, Vol.1 (29), p.5269-5279
Main Authors: Munaò, Gianmarco, O'Toole, Patrick, Hudson, Toby S, Costa, Dino, Caccamo, Carlo, Giacometti, Achille, Sciortino, Francesco
Format: Article
Language:English
Subjects:
Computer simulation
Formations
Janus
Mathematical models
Phase separation
Self assembly
Sporting goods
Strength
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Summary:We numerically investigate colloidal dimers with asymmetric interaction strengths to study how the interplay between molecular geometry, excluded volume effects and attractive forces determines the overall phase behavior of such systems. Specifically, our model is constituted by two rigidly-connected tangent hard spheres interacting with other particles in the first instance via identical square-well attractions. Then, one of the square-well interactions is progressively weakened, until only the corresponding bare hard-core repulsion survives, giving rise to a "Janus dumbbell" model. We investigate structure, thermodynamics and phase behavior of the model by means of successive umbrella sampling and Monte Carlo simulations. In most of the cases, the system behaves as a standard simple fluid, characterized by a gas-liquid phase separation, for sufficiently low temperatures. In these conditions we observe a remarkable linear scaling of the critical temperature as a function of the interaction strength. But, as the interaction potential approaches the Janus dumbbell limit, we observe the spontaneous formation of self-assembled lamellar structures, preempting the gas-liquid phase separation. Comparison with previous studies allows us to pinpoint the role of the interaction range in controlling the onset of ordered structures and the competition between the formation of these structures and gas-liquid condensation. Progressive modification of the fluid phase diagram of colloidal dimers, from symmetrical square-well to Janus dumbbells.
ISSN:1744-683X
1744-6848
DOI:10.1039/c4sm00544a