Rheological properties of mono- and polydomain liquid crystalline elastomers exhibiting a broad smectic A phase

Weilepp, Jochen; Stein, Peter; Aßfalg, N.; Finkelmann, Heino; Martinoty, P.; Brand, Helmut R.

doi:10.1209/epl/i1999-00417-3

Cited by 37 publications

(39 citation statements)

References 25 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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“…In this paper we shall find that the power law dependence is also effective in crosslinked LCE materials. In their parallel study of LCE, Gallani et al and Weilepp et al [8,9] also clearly stated that the rheological response did not change significantly when crossing an isotropicnematic phase boundary, whereas there has been a crucial change at the nematic-smectic A transition. The powerlaw frequency dependence of the elastic moduli has again been reported, with G ′ ∝ ω 0.3 in the smectic A phase.…”

Section: Introductionmentioning

confidence: 98%

Dynamic soft elasticity in monodomain nematic elastomers

Hotta

Terentjev

2003

Eur. Phys. J. E

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Abstract. We study the linear dynamic mechanical response of monodomain nematic liquid crystalline elastomers under shear in the geometry that allows the director rotation. The aspects of time-temperature superposition are discussed at some length and Master Curves are obtained between the glassy state and the nematic transition temperature Tni. However, the time-temperature superposition did not work through the clearing point Tni, due to change from the "soft-elasticity" nematic regime to the ordinary isotropic rubber response. We focus on the low-frequency region of the Master Curves and establish the power-law dependence of the modulus G ′ ∝ ω a . This law agrees very well with the results of static stress relaxation, where each relaxation curve obeys the analogous power law G ′ ∝ t −a in the corresponding region of long times and temperatures.

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“…Shear modulus measurements taken over a wide frequency range have begun recently. Gallani et al [9] have studied the behavior of polydomain elastomers with nematic and smectic-A phases, and Weilepp et al [10,11] that of poly-domain and monodomain elastomers which only have a smectic-A phase. For all the samples studied, the results obtained in the isotropic phase show that the real part of the shear modulus is the sum of two terms, one being frequency indea e-mail: martinot@fresnel.u-strasbg.fr pendent and associated with the permanent network, the other frequency dependent and giving rise to a scaling behavior (G ∼ G ∼ ω 0.5 ).…”

Section: Introductionmentioning

confidence: 99%

Shear modulus of polydomain, mono-domain and non-mesomorphic side-chain elastomers: Influence of the nematic order

Stein

Aßfalg²,

Finkelmann³

et al. 2001

The European Physical Journal E

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We investigate the behavior of the complex shear modulus of a series of elastomers including mono-domain and poly-domain liquid crystal samples, and a non-mesomorphic sample. We find that the dynamics of the glass transition are strongly modified by the nematic order. This result explains why the truly elastic response of liquid crystal elastomers can only be observed in the isotropic phase at very high temperatures and at very low frequencies. Between the elastic regime and the glassy state, the elastomers have a visco-elastic regime, which is characterized by a Rouse-like behavior for mono-domain and poly-domain samples, and by a Zimm-like behavior for the non-mesomorphic sample. We also show that the mono-domain sample exhibits marked anisotropy of the shear-modulus G . This anisotropy, which is observed for the first time, is a function of frequency and is inverted between low and high frequencies, due to relaxation effects of the orientational order.

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Rheological properties of mono- and polydomain liquid crystalline elastomers exhibiting a broad smectic A phase

Cited by 37 publications

References 25 publications

Shear Mechanical Properties of Main Chain Liquid Crystalline Elastomers

Shear Mechanical Properties of Main Chain Liquid Crystalline Elastomers

Dynamic soft elasticity in monodomain nematic elastomers

Shear modulus of polydomain, mono-domain and non-mesomorphic side-chain elastomers: Influence of the nematic order

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