Rheology of Liquid Crystalline Elastomers in Their Isotropic and Smectic A State

Weilepp, Jochen; Zanna, J. J.; Aßfalg, N.; Stein, Peter; Hilliou, L.; Mauzac, M.; Finkelmann, Heino; Brand, Helmut R.; Martinoty, P.

doi:10.1021/ma9900838

Cited by 44 publications

(57 citation statements)

References 30 publications

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“…The complex shear modulus G ¼ G 0 þ iG 00 was measured as a function of frequency using the piezorheometer used previously for studying the rheological properties of elastomers [3,4,[8][9][10][11][12] and polymers. [13,14] The principle of this apparatus consists in applying a small strain e to the film by means of a piezoelectric ceramic vibrating in the shear mode, and measuring the amplitude and the phase f of the shear stress s transmitted through the film using a second piezoelectric ceramic.…”

Section: Methodsmentioning

confidence: 99%

Shear Mechanical Properties of Main Chain Liquid Crystalline Elastomers

Rogez

Brandt²,

Finkelmann³

et al. 2006

Macro Chemistry & Physics

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Summary: The behavior of the complex shear modulus G = G′ + iG″ of a main chain liquid crystalline elastomer film oriented with the director in the plane of the film is investigated for the first time by shearing the film in a direction perpendicular or parallel to the director. The film exhibits a small mechanical anisotropy around the N‐I transition, which disappears slightly above TNI. A hydrodynamic softening of both G′⟂ and G′∥ (symbols ∥ and ⟂ refer to the direction of the director parallel, respectively perpendicular, to the shear displacement) is observed in the isotropic phase near TNI which is ascribed to the reorientation of the SmC domains revealed by X‐rays. These SmC domains are frozen‐in the temperature range investigated. They relax with a characteristic time which is deduced from the frequency dependence of the mechanical response of the film. It is shown that the time‐temperature superposition method does not apply and that there is no indication in favor of soft or semi‐soft elasticity. The influence of a static compression induced either mechanically on the film or by the shape change of the film as a function of temperature is also investigated. Data on the polydomain analogue complement this study.Temperature dependence of G′∥ and G′⟂ at 0.2 Hz for the monodomain film.imageTemperature dependence of G′∥ and G′⟂ at 0.2 Hz for the monodomain film.

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Section: Methodsmentioning

confidence: 99%

Shear Mechanical Properties of Main Chain Liquid Crystalline Elastomers

Rogez

Brandt²,

Finkelmann³

et al. 2006

Macro Chemistry & Physics

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“…It is not for polymers but liquids, and it is not a minirheometer because it needs a lot quantity of sample: a piezoelectric disc transducer is submerged in the liquid to do the measurements. Finally, there is another interesting rheometer, in researching state, made of piezoelectric transducers [5], [6], with the same basic operation principle of the piezoelectric minirheometer proposed in this paper (with the configuration of Fig. 2).…”

Section: Introductionmentioning

confidence: 93%

“…2). The difference is that, in the rheometer in [5] and [6], two glasses are included between the sample and the piezoelectric transducers in order to support the sample. With the piezoelectric minirheometer, the support glasses are suppressed, and the piezoelectric behaves as a support for the sample as well as a transducer, reducing the final size of the global system.…”

Section: Introductionmentioning

confidence: 99%

A Piezoelectric Minirheometer for Measuring the Viscosity of Polymer Microsamples

Sánchez

Prieto

Laso

et al. 2008

IEEE Trans. Ind. Electron.

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Abstract-This paper describes the electromechanical design, operating principles and performance of a rheometer able to characterize the rheological behavior of microsamples of viscoelastic materials, such as polymer solutions, melt, and rubbers. It was developed with a view to portability, robustness, and ease of operation for very small samples. The rheometer operates by subjecting the samples to small-amplitude sinusoidal strain rates via an inverse piezoelectric actuator and detecting the stress response of the material via a direct piezoelectric sensor. The device operates under frequency-sweep mode in a very wide range of frequencies. Required sample sizes are typically three orders of magnitude smaller than for conventional rheometers. Owing to its lack of moving parts, the rheometer has an extremely simple design and is insensitive to vibration. Measurements on pressuresensitive adhesives and other polymeric systems are presented and validated against a standard cone-and-plate rheometer.

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“…Several studies of the dynamic mechanical properties of SCLCE 3,5,8,[21][22][23][24][25][26][27][28][29][30][31] and MCLCE 6,7,[32][33][34] have appeared in recent years. MCLCE have a more direct coupling between backbone conformation and mesogen orientation compared with SCLCE, and the elasticity of MCLCE is significantly affected by the presence of hairpin folds.…”

Section: Introductionmentioning

confidence: 99%

“…21 Mechanical damping in smectic LCE is thought to be suppressed by the restricting effects of smectic layers, 26 leading to the assertion that the nematic phase is more attractive for design of vibration damping materials. 21 However, smectic main-chain linear polymers, 35,36 smectic SCLCE, 30,37 and smectic MCLCE 33 also exhibit high mechanical damping over certain ranges of temperature and frequency. The relaxation processes underlying the high damping may be quite different compared with those at work in a nematic LCE, leading to dramatic differences in the mechanical loss spectra.…”

Section: Introductionmentioning

confidence: 99%

Effects of structural imperfections on the dynamic mechanical response of main‐chain smectic elastomers

Patil

Hedden

2007

J Polym Sci B Polym Phys

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ABSTRACT:We examine the influence of structural imperfections on mechanical damping in polydomain smectic main-chain liquid crystalline elastomers (MCLCE) subjected to small strain oscillatory shear. The mechanical loss factor tan d ¼ G@(x)/ G 0 (x) exhibits a strong maximum (tan d % 1.0) near the smectic-isotropic (clearing) transition. ''Optimal'' elastomers that exhibit minimal equilibrium swelling in a good solvent are compared with highly swelling ''imperfect elastomers'' that contain higher concentrations of structural imperfections such as pendant chains. For the imperfect elastomers, tan d is markedly enhanced in the isotropic state because of relaxation of pendant chains and other imperfections. However, within the smectic state, the magnitude of tan d and its temperature dependence are similar for optimal and imperfect elastomers at x ¼ 1 Hz. The prominent loss peak near the clearing transition arises from segment-level relaxations that are insensitive to the details of chain connectivity. Smectic MCLCE can be tailored for applications as vibration-damping materials by manipulating the clearing transition temperature through the backbone structure or by deliberate introduction of structural imperfections such as pendant chains.

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Rheology of Liquid Crystalline Elastomers in Their Isotropic and Smectic A State

Cited by 44 publications

References 30 publications

Shear Mechanical Properties of Main Chain Liquid Crystalline Elastomers

Shear Mechanical Properties of Main Chain Liquid Crystalline Elastomers

A Piezoelectric Minirheometer for Measuring the Viscosity of Polymer Microsamples

Effects of structural imperfections on the dynamic mechanical response of main‐chain smectic elastomers

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