Physics of liquid crystals

Stephen, Michael J.; Straley, Joseph P.

doi:10.1103/revmodphys.46.617

Cited by 811 publications

(395 citation statements)

References 275 publications

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“…In the Maier-Saupe molecular field theory, the intermolecular interaction energy takes the form F 1 = − 1 2 U S 2 [17]. The parameter U is related to the nematic-isotropic phase transition temperature by the ratio, k B T N I = 0.22U .…”

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confidence: 99%

Orientational Coupling Amplification in Ferroelectric Nematic Colloids

et al. 2006

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We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy and capacitance studies. The resulting colloids normally remain homogeneous, but the nematic orientational coupling is significantly amplified. In particular cases, the nematic orientation coupling increases by 10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases up to 40 Celsius degrees compared to the pure LC host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.PACS numbers: 64.70. Md, 82.70.Dd, Colloids in which the solute is liquid crystalline (LC) are known to possess an extremely rich set of behaviors [1,2,3,4,5]. The anchoring between the LC and microcolloidal particles ( 1µm) can produce long-range orientational distortions around the particles. This results in strong inter-particle interactions -sometimes repulsive and sometimes attractive -in the mesophase. The interactions can give rise to well-ordered structures of particles in the liquid crystal matrix (both lattices and chains) [2,3]. However, in most cases a prerequisite for interesting LC colloidal behavior has been a high concentration dispersion, typically with particle volume fraction c part 30%. In such systems aggregated particles produce director distortions extending over macroscopic scales. These suspensions scatter light strongly, and possess unique structural, mechanical, electro-and magneto-optical properties [5,6].Recently, we have shown that even at low concentrations (c part 1%), LC colloids differ strongly from the pure host material [7,8,9,10]. These colloids consist of submicron ferroelectric particles suspended in the LC host. In these systems, unlike in classic LC colloids, the suspensionmatrix interaction is insufficient to disturb the LC orientation. This small concentration dramatically increases the dielectric anisotropy, significantly decreases the Freedericksz transition voltage, and significantly accelerates electric field-induced director reorientation.In this letter, we report results which show that these phenomena are general properties of liquid crystal suspensions containing ferroelectric colloidal nanoparticles. The addition of impurities normally decreases the nematic clearing temperature T N I [11]. However, our measurements show massive increases in T N I , of the order of 40 • C, for mass impurity concentrations of the order of 0.2%. These results imply an increase in the effective nematic interaction parameter. Measurements of the birefringence, dielectric anisotropy and order parameter in the suspension are consistent with this picture.We have also constructed a theoretical model. The ferroelectric particles in the suspension produce large electric fields in their neighborhood. These electric fields produce induce...

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Orientational Coupling Amplification in Ferroelectric Nematic Colloids

et al. 2006

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“…There is a vast body of work on the development of molecular theories for liquid crystals and associated computer simulation studies which has been collected and discussed from various perspectives in review literature [1,2,[5][6][7][8][9][10][11][12][13][14][15]. It is not our intention here to go through the different approaches in any detail but to highlight features which are relevant to our study.…”

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A generalisation of the Onsager trial-function approach: describing nematic liquid crystals with an algebraic equation of state

Franco-Melgar¹,

Haslam²,

Jackson³

2008

Molecular Physics

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“…In this work, we use the one-elastic-constant approximation, 17,26 where the splay, twist, and bend elastic constants have a common value K. In this approximation, the elastic free energy density reduces to…”

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confidence: 99%

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles

Grollau

Guzmán

Abbott

et al. 2004

The Journal of Chemical Physics

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Recent experiments indicate that liquid crystals can be used to optically report the presence of biomolecules adsorbed at solid surfaces. In this work, numerical simulations are used to investigate the effects of biological molecules, modeled as spherical particles, on the structure and dynamics of nematic ordering. In the absence of adsorbed particles, a nematic in contact with a substrate adopts a uniform orientational order, imposed by the boundary conditions at this surface. It is found that the relaxation to this uniform state is slowed down by the presence of a small number of adsorbed particles. However, beyond a critical concentration of adsorbed particles, the liquid crystal ceases to exhibit uniform orientational order at long times. At this concentration, the domain growth is characterized by a first regime where the average nematic domain size L D obeys the scaling law L D (t)ϳt 1/2 ; at long times, a slow dynamics regime is attained for which L D tends to a finite value corresponding to a metastable state with a disordered texture. The results of simulations are consistent with experimental observations.

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Physics of liquid crystals

Cited by 811 publications

References 275 publications

Orientational Coupling Amplification in Ferroelectric Nematic Colloids

Orientational Coupling Amplification in Ferroelectric Nematic Colloids

A generalisation of the Onsager trial-function approach: describing nematic liquid crystals with an algebraic equation of state

Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles

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