The study of uniaxial–biaxial phase transition of confined hard ellipsoids using density functional theory

Moradi, Mahmood; Ghotbabadi, B. Binaei; Aliabadi, Roohollah

doi:10.1142/s0129183117500681

Cited by 9 publications

(3 citation statements)

References 43 publications

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“…At { , q} {0.045, 0.058}, the I-(N 1 N 2 ) and (N 1 N 2 )-C CEP lines coincide, hence defining the I-(N 1 N 2 )-C CEP leading to a small nose-like region in which the N 1 -N 2 transition is stable (see Figure 9). This region is in agreement with the results reported by Aliabadi et al [70] using a canonical OnsagerParsons-Lee approach for colloidal discs-hard sphere mixtures to obtain the boundaries of the stable isostructural N 1 -N 2 transition regions. The I-N 1 -N 2 -C fourphase coexistence occurs along a curve of { , q} values from the I-(N 1 N 2 )-C CEP at { , q} {0.045, 0.058} towards the corner of the { , q} diagram.…”

Section: Multi-phase Coexistence Overviewsupporting

confidence: 92%

Depletion-driven four-phase coexistences in discotic systems

et al. 2018

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Free volume theory (FVT) is a versatile and tractable framework to predict the phase behaviour of mixtures of platelets and non-adsorbing polymer chains in a common solvent. Within FVT, three principal reference phases for the hard platelets are considered: isotropic (I), nematic (N) and columnar (C). We derive analytical expressions that enable us to systematically trace the different types of phase coexistences revealed upon adding depletants and confirm the predictive power of FVT by testing the calculated diagrams against phase stability scenarios from computer simulation. A wide range of multi-phase equilibria is revealed, involving two-phase isostructural transitions of all phase symmetries (INC) considered as well as the possible three-phase coexistences. Moreover, we identify the system parameters, relative disk shapes and colloid-polymer size ratios, at which four-phase equilibria are expected. These involve a remarkable coexistence of all three-phase states commonly encountered in discotics including isostructural coexistences I 1 -I 2 -N-C, I-N 1 -N 2 -C and I-N-C 1 -C 2 .

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Section: Multi-phase Coexistence Overviewsupporting

confidence: 92%

Depletion-driven four-phase coexistences in discotic systems

et al. 2018

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“…Over the years, anisotropic colloidal particles have been investigated experimentally [1,2,3,4], theoretically [5,6,7,8] and using computer simulations [9,10]. Despite numerous studies on anisotropic colloidal particles, the bulk and confined properties of colloidal systems are still very interesting from both scientific and industrial point of views due to their stimulating phase behaviors and to the convenient alignment of the anisotropic molecules by surfaces and external electric (magnetic) fields [11,12].…”

Section: Introductionmentioning

confidence: 99%

Biaxial layering transition of hard rodlike particles in narrow slitlike pores

et al. 2018

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The phase behaviour of hard rectangular rods with length L and diameter D is studied in a narrow slit-like pore using the Parsons-Lee density functional theory. Using the restricted orientation approximation, we find strong adsorption at the walls with planar ordering, second order uniaxial-biaxial ordering transitions and first order layering transitions. The layering transition takes place between two fluids having n and n+1 layers, where the layer spacing is in the order of D. In the case of weak shape anisotropy (L/D=3), the coexisting fluids can be either uniaxial or biaxial, while both phases are found to be biaxial for L/D=6and L/D=9. Interestingly, even two or more layering transitions can be observed with increasing density at a given shape anisotropy and pore width. *

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“…Although the discovery of liquid crystals (LCs) dates back more than a century ago, LCs are still studied eagerly in an effort to search for new materials that meet the constantly growing need of applications in biosensors and organic transistors [1,2] and to further our scientific understanding self-organization of soft condensed matter in the presence of external fields such as geometric confinement [3][4][5]. As a benchmark model colloidal particles with a simple non-isotropic shape, such as rods and discs, have been analyzed extensively in theory [6][7][8][9], experiment [10,11] and by computer simulation [12][13][14]. Onsager (1949) [15,16] argued that the key factor in the formation of liquid crystalline structures is the anisotropic shape of the particles for which simple geometrical shapes are usually considered, such as ellipsoids [13,17] cylindrical rods [18], cut spheres [19], or parallelepipeds [20,21].…”

Section: Introductionmentioning

confidence: 99%

Capillary-driven biaxial planar and homeotropic nematization of hard cylinders

2022

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We use the Parsons-Lee modification of Onsager's second virial theory within the restricted orientation (Zwanzig) approximation to analyse the phase behaviour of hard cylindrical rods confined in narrow pores. Depending on the wall-to-wall separation we predict a number of distinctly different surfacegenerated nematic phases, including a biaxial planar nematic with variable number of layers, a monolayer homeotropic, and a hybrid T-type structure (a planar layer combined with a homeotropic one). For narrow pores, we find evidence of two types of second-order uniaxial-biaxial transitions depending on the aspect ratio of the particles. More specifically, we observe a continuous cross-over from n to n+1 layers each with a distinct planar anchoring symmetry as well as first-order transitions from planar to homeotropic surface anchoring. Contrary to the previously studied case of parallelepipeds we find that the surface anchoring transition from planar to homeotropic symmetry occurs at much lower overall rod packing fractions. This renders the observation of homeotropic capillary nematics much more realistic in experimental systems of strongly confined anisotropic colloids. Unlike confined parallelepipeds, cylindrical rods gradually increase the number of the nematic planar layers (without any phase transitions). However, a weak first order transition was observed between two planar structures with n and n+1 layers in wide pores and longer rods. In addition, the cylindrical rods exhibit a first-order transition from the homeotropic structure to the uniaxial (or biaxial) T phase that has not been observed in confined hard parallelepipeds. We further demonstrate a reentrant uniaxial-biaxial-uniaxial-biaxal phase sequence for confined cylinders at small aspect ratio. Our results also clearly demonstrate that stable T-type surface ordering is a subtle capillary effect that only becomes manifest in sufficiently narrow pores away from the 2D bulk limit.

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The study of uniaxial–biaxial phase transition of confined hard ellipsoids using density functional theory

Cited by 9 publications

References 43 publications

Depletion-driven four-phase coexistences in discotic systems

Depletion-driven four-phase coexistences in discotic systems

Biaxial layering transition of hard rodlike particles in narrow slitlike pores

Capillary-driven biaxial planar and homeotropic nematization of hard cylinders

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