Anisotropic mechanical properties of a polymer nematic liquid crystal (original) (raw)
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Induced chain rigidity, splay modulus and other properties of nematic polymer liquid crystals
Macromolecules, 1988
We present a numerical analysis of the induced chain rigidity or global persistence length, the order parameter, the splay modulus, and other properties of a polymer nematic. The macromolecules are viewed as long slender wormlike cylinders interacting via hard-core repulsions in the second virial approximation. We calculate the orientational distribution function from the nonlinear integrodifferential equation first formulated by Khokhlov
Measurements of the anisotropic viscous and elastic properties of lyotropic polymer nematics
Faraday Discussions of the Chemical Society, 1985
We summarize the current status of our studies of the macroscopic linear mechanical properties of nematic liquid crystals formed from solutions of rigid or semirigid rod-like polymers. The polymer system we have studied is a racemic mixture of poly(benzy1 glutamate) dissolved in a mixture of dioxane and methylene chloride. We have also studied nematics formed from colloidal suspensions of tobacco mosaic virus which may be viewed as an ideal model system representing a rigid-rod polymer solution. We review briefly the current 125
Disclination core structure in rigid and semiflexible main-chain polymer nematic liquid crystals
Macromolecules, 1993
In order to ascertain the near-core structure of fl/* wedge disclinations, the apparent splay and bend elastic anisotropy, tapp, is measured as a function of radial distance from the singularity. eapp = [(k& -( k 3 3 ) a l / [ ( k~~) a + (k3&1. Both a rigid and a semiflexible main-chain liquid crystal polyester are studied. Results demonstrate a special structure of the core at radii less than about several molecular lengths.
Journal of Polymer Science Part B: Polymer Physics, 1995
The twist and bend viscosities of dilute solutions of cyclic and hyperbranched liquid crystal polymers (LCP) dissolved in low molar mass nematic solvents were determined via dynamic light scattering analysis. These results were compared to those of linear chains with similar chemical repeat structures. The nematic solvent used was 4′‐pentyloxy‐4‐cyanobiphenyl (50CB). The cyclic LCP oligomers, Cy TPB10, have a mesogenic group, 1‐(4‐hydroxy‐4′‐biphenyl)‐2‐(4‐hydroxyphenyl) butane, separated by flexible decamethylene spacers. The twist viscosity of the cyclic Cy‐TPB10 oligomers increases with molecular weight more strongly than the linear, TPB‐10, suggesting that the hydrodynamic behavior of Cy‐TPB10 is closer to that of a rigid rod than TPB10. Surprisingly, the intrinsic bend viscosity [ηbend] of Cy‐TPB10 decreases with molecular weight, in contrast to the positive dependence for linear TPB10. This may reflect the higher strain energy in the smaller ring sizes. The hyperbranched LCP, ...
Elastic constants and orientational viscosities of a bent-core nematic liquid crystal
Physical Review E, 2011
Using a combination of dynamic light scattering and Freedericksz transitions induced in applied magnetic and electric fields, we have determined the absolute magnitudes of the Frank elastic constants and effective orientational viscosities of the bent-core nematic liquid crystal, 4-chloro-1,3-phenylene bis 4-[4'-(9-decenyloxy)benzoyloxy] benzoate. At a fixed temperature 2 • C below the isotropic-nematic transition, we find K 11 = 3.1 × 10 −12 N, K 22 = 0.31 × 10 −12 N, K 33 = 0.88 × 10 −12 N, η splay = 1.1 Pa s, η twist = 0.37 Pa s, and η bend = 1.2 Pa s. The unusual anisotropies of these parameters are discussed in terms of short-range, smectic-C-like correlations among molecules in the nematic phase.
Viscoelasticity of nematic liquid crystals at a glance
Soft Matter, 2014
A new microscopy method is demonstrated for the characterisation of the viscoelasticity of nematic liquid crystals. Both aligned and spatially disordered samples are studied successfully. Several other heterogeneous soft materials could be studied with this approach.
The European Physical Journal E, 2001
The Frank elasticity constants which describe splay (K1), twist (K2), and bend (K3) distortion modes are investigated for 4-n-pentyl-4 -cyanobiphenyl (5CB) in the nematic liquid crystal. The calculations rest on statistical-mechanical approaches where the absolute values of Ki (i = 1, 2, 3) are dependent on the direct correlation function (DCF) of the corresponding nematic state. The DCF was determined using the pair correlation function by solving the Ornstein-Zernike equation. The pair correlation function, in turn, was obtained from molecular dynamics (MD) trajectory. Three different approaches for calculations of the elasticity constants were employed based on different level of approximation about the orientational order and molecular correlations. The best agreement with experimental values of elasticity constants was obtained in a model where the full orientational distribution function was used. In addition we have investigated the approximation about spherical distribution of the intermolecular vectors in the nematic phase, often used in derivation of various mean-field theories and employed here for the construction of the DCF. We found that this assumption is not strictly valid, in particular a strong deviation from the isotropic distribution is observed for short intermolecular distances. .Cz Theory and models of liquid crystal structure
Linear Viscoelasticity of Leslie-Ericksen Liquid Crystal Polymers
2004
The linear viscoleasticity of seven lyotropic and thermotropic liquid crystalline polymers is characterized using the Leslie-Ericksen equations of defect-free nematodynamics for small amplitude oscillatory capillary Poiseuille flow, and using analytical, numerical and scaling methods. The experimental data sets used in this study correspond to the six Leslie viscosities coefficients for seven nematics liquid crystal polymers, that include shear flow-aligning and non-aligning materials. The predicted equivalent rheological responses between the shear flow-aligning and shear non-aligning polymers demonstrate the universality of nematodynamics. In this work the principles of superposition are developed, applied, and shown to be accurate in collapsing the data sets for both classes of polymers. The scaled resonance peak in the loss tangent (tan δ=G”/G’) as a function of the oscillation frequency shown to be a universal constant for monodomain nematics. Introduction The Leslie-Ericksen l...
Nonlinear curvature elasticity of nematic liquid crystals
arXiv: Soft Condensed Matter, 2018
The nonlinear elastic properties of nematic liquid crystals have acquired new interest with the recent experimental observation of bulk modulated nematic phases which are composed by achiral molecules. We extend the Oseen-Zocher-Frank's elastic theory for nematic liquid crystals by including gradients of the nematic strain tensor in the elastic deformation energy. The invariants of the elastic tensor fields, up to the fourth order in the nematic director spatial derivatives, are calculated. An alternative approach that consists in the extension of the linear elastic energy to higher powers of the nematic strain tensor, as in classical elasticity of solids, is also developed. The twist-bend nematic modulated phase is investigated by both approaches and the results are critically compared. The conical angle of the twist-bend phase is calculated as function of the elastic constants. Surface-like effects are considered. Finally, we demonstrate that a splay-bend nematic phase with sm...
Flow properties of a twist-bend nematic liquid crystal
RSC Adv., 2014
We present the first shear alignment studies and rheological measurements in the twist-bend nematic (N tb ) liquid crystal phase of odd numbered flexible dimer molecules. It is found that the N tb phase is strongly shear-thinning. At shear stresses below 1 Pa the apparent viscosity of N tb is 1000 times larger than in the nematic phase. At stress above 10 Pa the N tb viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. This is consistent with the heliconic axis becoming normal to the shear plane via shear-induced alignment. From measurements of the dynamic modulus we estimate the compression modulus of the pseudo-layers to be B $ 2 kPa; this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy.