Nematic solutions of nematic side chain polymers : twist viscosity effect in the dilute regime

Abstract

Nous avons montré que la viscosité de torsion d'un nématique est notablement augmentée par l'addition de chaines polymériques, même à faible concentration. Cet effet est analysé en fonction de la longueur des chaines et du paramètre d'ordre. Les résultats expérimentaux sont en bon accord avec un modèle qui implique une conformation anisotrope du polymère; ils conduisent à une estimation numérique de cette anisotropie, qui semble suffisamment importante pour pouvoir être mesurée directement par une méthode de diffusion aux petits angles.

Molecular Weight-Dependent Behavior of the Twist Distortion in a Nematic Monodomain Containing a Main-Chain Liquid Crystal Polymer

“…To discuss the experimental results in terms of the molecular chain configuration and hydrodynamic behavior, we first recall the theoretical prediction of Brochard:20 hi = (ClVA/M)[X||X1fi||2/?x2/(X||fi"2 + 2)]( "2-Rx2)2KR2Rx2) (4) where C is the polymer concentration in g/mL; ZVA is Avogadro's number; M is the molecular weight of the polymer; Xy and X x are respectively the friction coefficients associated with motions parallel and perpendicular to the director; and R\\ and i?x are the radii of gyration parallel and perpendicular to the director, respectively. Assuming a free-draining condition to be valid for the oligomers and for the highly extended polymer chains, we may write Xy = LZy and Xx = LZ ,20 where Z\\ and Zx are the unit length friction coefficients in the two orthogonal directions.…”

“…Such properties have been intensively studied recently. [3][4][5][6][7][8][9][10][11][12][13][14] The elastic constants and viscosity coefficients which characterize the splay, twist, and bend distortions of the nematic solution can be determined via the associated Freedericksz transition characteristics under magnetic or electric fields16• 16 and by static and dynamic light scattering measurements.3 •17-19 Finally, a theoretical model has been developed by Brochard20 which provides expressions for certain viscosity increments as a function of fig and fij.. Of particular interest to us in the following study is the possibility, pointed out in a recent theoretical model of chain configuration in the nematic state,21 that a mainchain LCP may exhibit behavior ranging from rodlike to random-coil statistics depending upon the ratio of the persistence length to the chain contour length even in a strong nematic field. To gain insight into the chain statistics, the relationship between the molecular weight and radii of gyration or the viscosity increments must be obtained for LCPs of narrow polydispersity.…”

Temperature and Molecular Weight Dependence of the Viscometric Properties of Main-Chain Liquid Crystal Polymers in Nematic Solvents

“…These corrected molecular weights were further used to calculate the chain contour lengths of TPB10 polymers. 4'-(Pentyloxy) -4-cyanobiphenyl (50CB, Tni = 67 °C) previously shown24 to be a nematic solvent for TPB10 and TPB13, was obtained from Aldrich Chemical Co. 4'-Pentyl-4-cyanobiphenyl (5CB, Tni = 34.8 °C), which we find via the contact method24 to be a solvent for TPB10 oligomers (but not for TPB10 polymers24) and TPB13, was purchased from BDH Ltd. All materials were used as received without further purification. Planar (homogeneous) monodomains, in which the average molecular direction is parallel to the glass surfaces, were prepared using rubbed polyimide-coated conductive glass slides graciously supplied to us by Mr. Pat Dunn at Kent State University, Kent, Ohio.…”

“…Recently, there has been interest in investigating the viscoelastic properties of nematic solutions containing a LCP dissolved in a nematic solvent, which are expected to be a sensitive function of the LCP molecular architecture. [3][4][5][6][7][8][9][10][11][12][13][14][15] The elastic constants and viscosity coefficients which characterize the splay, twist, and bend distortions of the nematic solution can be determined via the associated Freedericksz transition characteristics under magnetic or electric fields,16,17 and by static and dynamic light scattering measurements, 3,[18][19][20] in each case performed on nematic monodomains. A theoretical model developed by Brochard21 provides expressions which express certain viscosity increments as a function of the mean square end-to-end distances R 2 and R_l2.…”

Odd-even effect in the viscoelastic properties of main-chain liquid crystal polymer-low-molar-mass nematogen mixtures

“…Figure10. Temperature dependence of intrinsic splay viscosity for 1% TPB-9, 1% TPB-10, 1% TPB-14, and 1% TPB-15 mixtures.…”