Peculiarities of δ- and α-relaxations in thermotropic side chain liquid crystalline polymers with and without nematic reentrant phase

Salehli, F.; Yildiz, Sevtap; Özbek, Haluk; Uykur, Ece; Gürsel, Yeşim Hepuzer; Durmaz, Yasemin Yüksel

doi:10.1016/j.polymer.2009.12.029

Cited by 6 publications

(6 citation statements)

References 31 publications

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“…We assume that this peculiarity originates from the antiparallel cooperative interaction between the CB mesogens through the strong dipole (4.05 D) interaction. Peculiarities of CB mesogens for the aggregation structure have also been found in the assembly process of low-molecular-mass LCs and relaxation behavior in polymer LCs . Presumably, the existence of firmly remaining planar mesogens is related to the stabilized antiparallel bilayer formation.…”

Section: Results and Discussionmentioning

confidence: 90%

“…Peculiarities of CB mesogens for the aggregation structure have also been found in the assembly process of low-molecular-mass 40 LCs and relaxation behavior in polymer LCs. 41 Presumably, the existence of firmly remaining planar mesogens is related to the stabilized antiparallel bilayer formation. Planarly anchored (adsorbed) mesogens in contact with the substrate surface can induce the parallel orientation of a considerable amount of neighboring CB mesogens through the strong cooperativity.…”

Section: Contact Angle Measurementsmentioning

confidence: 99%

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Evaluations of Mesogen Orientation in Thin Films of Polyacrylate with Cyanobiphenyl Side Chain

Tanaka¹,

Mizuno²,

Hara³

et al. 2016

Langmuir

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The orientation behavior of mesogens in a polyacrylate with cyanobiphenyl (CB) side chain in thin films was investigated in detail by UV-vis absorption spectroscopy and grazing incidence small-angle X-ray scattering (GI-SAXS) measurements using both high-energy X-rays of Cu Kα line (λ = 0.154 nm) and low-energy synchrotron X-rays (λ = 0.539 nm). By changing the film thickness ranging 7-200 nm, it is concluded that the planar orientation is predominant for thin films with thickness below 10-15 nm. This planar mesogen orientation near the substrate surface coexists with the homeotropically aligned CB mesogens in films thicker than 30 nm. For the thinnest 7 nm film, the planar orientation is unexpectedly lost, which is in consort with a disordering of smectic layer structure. Peculiar orienting characteristics of CB mesogen are suggested, which probably stem from the tendency to form an antiparallel arrangement of mesogens due to the strong dipole moment of the terminal cyano group.

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Section: Results and Discussionmentioning

confidence: 90%

Section: Contact Angle Measurementsmentioning

confidence: 99%

Evaluations of Mesogen Orientation in Thin Films of Polyacrylate with Cyanobiphenyl Side Chain

Tanaka¹,

Mizuno²,

Hara³

et al. 2016

Langmuir

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show abstract

“…This Debye-relaxation coincides with the presence of electrode polarization, as observed by a low-frequency increase in

. We thus interpret this relaxation peak as arising from so-called conductivity relaxation [ 43 , 53 ], due to electrode polarization, and thus not to a molecular relaxation; electrode polarization is due to charge accumulation at the sample-electrode interface [ 22 ]. Given the interference from DC-conductivity and electrode polarization at low frequencies, we cannot completely rule out that a slow

process exists.…”

Section: Resultsmentioning

confidence: 99%

“…The structural (

) relaxation in SCLCPs involves the backbone polymer segments and is directly related to the glass transition [ 22 , 40 ]. The

process has been observed in both SCLCPs [ 22 , 41 , 42 , 43 ] and LCEs [ 37 , 38 , 39 ] and is typically slower than the

relaxation, follows a VFT dependence, and is attributed to reorientation of the mesogenic units around the polymer backbone. The faster secondary relaxations, typically termed

and

are generally assigned to motions of the mesogenic units, where the

relaxation is typically assigned to fluctuations of the mesogen around its molecular long axis [ 22 , 41 , 44 , 45 ], and the

relaxation is assigned to motions of either the spacer unit, or the terminal group of the side-chain mesogen [ 40 , 41 ].…”

Section: Introductionmentioning

confidence: 99%

Influence of Liquid Crystallinity and Mechanical Deformation on the Molecular Relaxations of an Auxetic Liquid Crystal Elastomer

et al. 2021

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Liquid Crystal Elastomers (LCEs) combine the anisotropic ordering of liquid crystals with the elastic properties of elastomers, providing unique physical properties, such as stimuli responsiveness and a recently discovered molecular auxetic response. Here, we determine how the molecular relaxation dynamics in an acrylate LCE are affected by its phase using broadband dielectric relaxation spectroscopy, calorimetry and rheology. Our LCE is an excellent model system since it exhibits a molecular auxetic response in its nematic state, and chemically identical nematic or isotropic samples can be prepared by cross-linking. We find that the glass transition temperatures (Tg) and dynamic fragilities are similar in both phases, and the T-dependence of the α relaxation shows a crossover at the same T* for both phases. However, for T>T*, the behavior becomes Arrhenius for the nematic LCE, but only more Arrhenius-like for the isotropic sample. We provide evidence that the latter behavior is related to the existence of pre-transitional nematic fluctuations in the isotropic LCE, which are locked in by polymerization. The role of applied strain on the relaxation dynamics and mechanical response of the LCE is investigated; this is particularly important since the molecular auxetic response is linked to a mechanical Fréedericksz transition that is not fully understood. We demonstrate that the complex Young’s modulus and the α relaxation time remain relatively unchanged for small deformations, whereas for strains for which the auxetic response is achieved, significant increases are observed. We suggest that the observed molecular auxetic response is coupled to the strain-induced out-of-plane rotation of the mesogen units, in turn driven by the increasing constraints on polymer configurations, as reflected in increasing elastic moduli and α relaxation times; this is consistent with our recent results showing that the auxetic response coincides with the emergence of biaxial order.

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“…hydrogen bonding [1][2][3][4] or electrostatic interaction. [5][6][7] Various function tectonic units varying from metal ions, 4,8 quantum dots 3 to organic dyes 9 were reported to be employed to prepare materials with various functions.…”

Section: Introductionmentioning

confidence: 99%

Formation and properties of liquid crystalline supramolecules with anisotropic fluorescence emission

Lü

et al. 2014

Polym. Chem.

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Peculiarities of δ- and α-relaxations in thermotropic side chain liquid crystalline polymers with and without nematic reentrant phase

Cited by 6 publications

References 31 publications

Evaluations of Mesogen Orientation in Thin Films of Polyacrylate with Cyanobiphenyl Side Chain

Evaluations of Mesogen Orientation in Thin Films of Polyacrylate with Cyanobiphenyl Side Chain

Influence of Liquid Crystallinity and Mechanical Deformation on the Molecular Relaxations of an Auxetic Liquid Crystal Elastomer

Formation and properties of liquid crystalline supramolecules with anisotropic fluorescence emission

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