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.

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

GIACOMETTI, Achille;
2014-01-01

Abstract

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.
2014
10
File in questo prodotto:
File Dimensione Formato  
Munao_SoftMatter_14.pdf

non disponibili

Descrizione: Munao_SoftMatter_2014
Tipologia: Documento in Post-print
Licenza: Accesso chiuso-personale
Dimensione 1.31 MB
Formato Adobe PDF
1.31 MB Adobe PDF   Visualizza/Apri

I documenti in ARCA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10278/40633
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 33
  • ???jsp.display-item.citation.isi??? 33
social impact