The Frank constants of some nematic liquid crystals

Bradshaw, M. J.; Raynes, E. P.; Bunning, John D.; Faber, T. E.

doi:10.1051/jphys:019850046090151300

Cited by 203 publications

(78 citation statements)

References 13 publications

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“…To check for systematic effects, we compared our values for (K 1 + K 3 ) with those reported by Bradshaw et al who measured K 1 and K 3 using two different methods. 63 We interpolated and averaged their two data sets (Table I in Ref. 63) and found that the resultant values of (K 1 + K 3 ) differ from ours by, on average, 0.8 %.…”

Section: B Elastic Coefficientsmentioning

confidence: 77%

“…63 We interpolated and averaged their two data sets (Table I in Ref. 63) and found that the resultant values of (K 1 + K 3 ) differ from ours by, on average, 0.8 %. This suggests that our measurements of (K 1 + K 3 ) are relatively free from significant systematic effects, and our value of 0.6 % is indeed a reasonable estimate of our combined standard uncertainty.…”

Section: B Elastic Coefficientsmentioning

confidence: 77%

“…K 1 and K 3 were measured using the standard capacitance technique on a planar aligned nematic cell undergoing a Fréedericksz transition. [63][64][65][66][67] The capacitance was measured using a Precision Component Analyzer (6440A, Wayne Kerr Electronics) at a frequency of 600 Hz-the same frequency at which the flexoelectrooptic measurements were taken. The cells used here were 20 μm thick with planar alignment, supplied by Instec (LC2-20.0).…”

Section: B Elastic Coefficientsmentioning

confidence: 99%

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Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

et al. 2012

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Section: B Elastic Coefficientsmentioning

confidence: 77%

Section: B Elastic Coefficientsmentioning

confidence: 77%

Section: B Elastic Coefficientsmentioning

confidence: 99%

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Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

et al. 2012

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“…where ε 0 is the vacuum permittivity, and K 11 = 6.65 pN (ref 17) and ε a = 11.5 (ref 18) are the splay elastic constant and dielectric anisotropy of 5CB at 23°C, respectively. Any force exerted on the silver surfaces by either the attractive oppositely charged surfaces or induced by the liquid crystal will be measured by the 3D actuator−sensor attachment to the SFA.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Simultaneous Measurements of Molecular Forces and Electro-Optical Properties of a Confined 5CB Liquid Crystal Film Using a Surface Forces Apparatus

Kristiansen¹,

Zeng

Zappone³

et al. 2015

Langmuir

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Using a surface forces apparatus (SFA), we studied the forces associated with the reorientation of molecules of a common nematic thermotropic liquid crystal, 4′-n-pentyl-4-cyanobiphenyl (5CB), confined between two conducting (silver) surfaces and its optical behavior under the influence of electric fields with varying magnitudes and field directions. A transient attractive force was observed due to partial reorientations of the liquid crystal molecules and the flow of free ions, in addition to a stronger constant capacitance attraction between the silver surfaces. At the same time, the optical properties of the liquid crystals were observed perpendicular to the silver surfaces. Observations of shifts and fluctuations of the extraordinary wave of the (multiple beam) interference fringes measure the refractive index of the director component parallel to the surface, which is sensitive to tilt motion (or reorientation) of the liquid crystal molecules that provided details of the anisotropic orientations of the molecules and domains. Any lateral differential refractive index change is easily observed by optical microscopy. The optical microscope imaging showed that the changes in the optical properties are due to convective flow at domain boundaries of the liquid crystal molecules (and possible free ions) between the two charged surfaces. At low electric fields, propagation of domain boundaries was observed, while at higher electric fields, hexagonal patterns of flowing molecules were observed. The interplay of the force measurements and optical observations reveal a complex dynamic behavior of liquid crystals subjected to varying electric fields in confined spaces.

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“…For traditional nematics at temperatures in a wide range below the clearing temperature, the bend modulus II is on the order of 10 Ϫ12 J/m and is three-halves to two times the splay modulus I . [11][12][13][14] The values of these moduli have not yet been determined for nematic elastomers, but, because of the rubbery nature of these materials, it seems reasonable to expect that the moduli would be at least an order of magnitude greater. 15 So, we took I ϭ10 Ϫ11 J/m and II ϭ2ϫ10 Ϫ11 J/m.…”

Section: ͑22͒mentioning

confidence: 99%

Biaxial disclinated states in nematic elastomers

Fried

Korchagin

Todres

2003

The Journal of Chemical Physics

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We use a continuum model to investigate the isochoric axial contraction and expansion of a right circular cylindrical specimen composed of a nematic elastomer that is cross-linked in a uniaxial state and then annealed. We build on previous work by relaxing the constraint that the molecular conformation be spherical or uniaxial, allowing instead for biaxiality. The material exhibits an energetic preference for states involving a disclination of strength ϩ1 along the cylinder axis surrounded by a region in which the conformation of the polymer chains is indeed biaxial. We show that such states represent minimizers of the total free-energy. Also, the reactive pressure necessary to enforce the constraint of material incompressibility within the disclination core is found to be reduced by an order of magnitude when the conformation is biaxial rather than uniaxial. A bifurcation analysis is used to analytically determine the thresholds of axial expansion and contraction at which the material prefers a disclinated state. These thresholds are found to be consistent with numerical predictions. Finally, the stability of the solutions for the studied parameters is also investigated.

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The Frank constants of some nematic liquid crystals

Cited by 203 publications

References 13 publications

Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

Flexoelectric coefficient measurements in the nematic liquid crystal phase of 5CB

Simultaneous Measurements of Molecular Forces and Electro-Optical Properties of a Confined 5CB Liquid Crystal Film Using a Surface Forces Apparatus

Biaxial disclinated states in nematic elastomers

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