Monte Carlo computer simulations are carried out for a model system of like-charged colloidal platelets in the isothermal-isobaric ensemble (NpT). The aim is to elucidate the role of electrostatic interactions on the structure of synthetic clay systems at high particle densities. Short-range repulsions between particles are described by a suitable hard-core model representing a discotic particle. This potential is supplemented with an electrostatic potential based on a Yukawa model for the screened Coulombic potential between infinitely thin disklike macro-ions. The particle aspect-ratio and electrostatic parameters were chosen to mimic an aqueous dispersion of thin, like-charged, rigid colloidal platelets at finite salt concentration. An examination of the fluid phase diagram reveals a marked shift in the isotropic-nematic transition compared to the hard cut-sphere reference system. Several statistical functions, such as the pair correlation function for the center-of-mass coordinates and structure factor, are obtained to characterize the structural organization of the platelets phases. At low salinity and high osmotic pressure we observe anomalous hexagonal columnar structures characterized by interpenetrating columns with a typical intercolumnar distance corresponding to about half of that of a regular columnar phase. Increasing the ionic strength leads to the formation of glassy, disordered structures consisting of compact clusters of platelets stacked into finite-sized columns. These so-called “nematic columnar” structures have been recently observed in systems of charge-stabilized gibbsite platelets. Our findings are corroborated by an analysis of the static structure factor from a simple density functional theory.
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21 January 2012
Research Article|
January 17 2012
Anomalous columnar order of charged colloidal platelets
L. Morales-Anda;
L. Morales-Anda
1Departamento de Ingeniería Física, División de Ciencias e Ingenierías Campus León,
Universidad de Guanajuato
, Colonia Lomas del Campestre, León 37150, México
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H. H. Wensink;
H. H. Wensink
2Institute for Theoretical Physics: Soft Matter,
Heinrich-Heine-University-Düsseldorf
, Universitätsstraße 1, 40225, Düsseldorf, Germany
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A. Galindo;
A. Galindo
3Department of Chemical Engineering,
Imperial College London
, South Kensington Campus, London SW7 2AZ, United Kingdom
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A. Gil-Villegas
A. Gil-Villegas
a)
1Departamento de Ingeniería Física, División de Ciencias e Ingenierías Campus León,
Universidad de Guanajuato
, Colonia Lomas del Campestre, León 37150, México
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a)
Electronic mail: gil@fisica.ugto.mx.
J. Chem. Phys. 136, 034901 (2012)
Article history
Received:
September 04 2011
Accepted:
December 12 2011
Citation
L. Morales-Anda, H. H. Wensink, A. Galindo, A. Gil-Villegas; Anomalous columnar order of charged colloidal platelets. J. Chem. Phys. 21 January 2012; 136 (3): 034901. https://doi.org/10.1063/1.3673877
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