Effect of polydispersity and soft interactions on the nematic versus smectic phase stability in platelet suspensions
Entity
UAM. Departamento de Física Teórica de la Materia CondensadaPublisher
American Institute of PhysicsDate
2011-03-28Citation
10.1063/1.3570964
Journal of Chemical Physics 134.12 (2011): 124904
ISSN
0021-9606 (print); 1089-7690 (online)DOI
10.1063/1.3570964Funded by
This work has been partly financed by grants NANOFLUID, MOSAICO, and MODELICO from Comunidad Autónoma de Madrid (Spain), and Grant Nos. FIS2007-65869-C03-01, FIS2008-05865-C02-02, FIS2010-22047-C05-01, and FIS2010-22047-C05-04 from Ministerio de Educación y Ciencia (Spain)Project
Comunidad de Madrid. S2009/ESP-1691/MODELICOEditor's Version
http://dx.doi.org/10.1063/1.3570964Subjects
Aqueous solvents; Attractive force; Charged platelets; Columnar phase; Depletion interactions; Nematic and smectic ordering; Nematic phase; Nonabsorbing polymers; Screened Coulomb interaction; Smectic phase; Temperature shift; Tricritical point; FísicaNote
The following article appeared in Journal of Chemical Physics 134.12 (2011): 124904 and may be found at http://scitation.aip.org/content/aip/journal/jcp/10.1063/1.3570964Rights
© 2011 American Institute of PhysicsAbstract
We theoretically discuss, using density-functional theory, the phase stability of nematic and smectic ordering in a suspension of platelets of the same thickness but with a high polydispersity in diameter, and study the influence of polydispersity on this stability. The platelets are assumed to interact like hard objects, but additional soft attractive and repulsive interactions, meant to represent the effect of depletion interactions due to the addition of nonabsorbing polymer, or of screened Coulomb interactions between charged platelets in an aqueous solvent, respectively, are also considered. The aspect (diameter-to-thickness) ratio is taken to be very high, in order to model solutions of mineral platelets recently explored experimentally. In this regime a high degree of orientational ordering occurs; therefore, the model platelets can be taken as completely parallel and are amenable to analysis via a fundamental-measure theory. Our focus is on the nematic versus smectic phase interplay, since a high degree of polydispersity in diameter suppresses the formation of the columnar phase. When interactions are purely hard, the theory predicts a continuous nematic-to-smectic transition, regardless of the degree of diameter polydispersity. However, polydispersity enhances the stability of the smectic phase against the nematic phase. Predictions for the case where an additional soft interaction is added are obtained using mean-field perturbation theory. In the case of the one-component fluid, the transition remains continuous for repulsive forces, and the smectic phase becomes more stable as the range of the interaction is decreased. The opposite behavior with respect to the range is observed for attractive forces, and in fact the transition becomes of first order below a tricritical point. Also, for attractive interactions, nematic demixing appears, with an associated critical point. When platelet polydispersity is introduced the tricritical temperature shifts to very high values
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Google Scholar:Velasco Caravaca, Enrique
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Martínez-Ratón, Yuri
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