Comparison of the Molecular Dynamics of a Liquid Crystalline Side Group Polymer Revealed from Temperature Modulated DSC and Dielectric Experiments in the Glass Transition Region

Schick, Christoph; Sukhorukov, D. I.; Schönhals, Andreas

doi:10.1002/1521-3935(20010501)202:8<1398::aid-macp1398>3.0.co;2-c

Cited by 28 publications

(15 citation statements)

References 20 publications

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“…This tumbling mode is located at higher frequencies than the d process. While there has been controversy concerning which of these two processes is responsible for glassy dynamics in glassforming LCs, recent experiments 26,29 have helped identify the tumbling mode as being the underlying process. A comparison between BDS data in the present work and temperature modulated DSC data published elsewhere 30 (see activation plots) conrms this nding for itraconazole.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics of itraconazole confined in thin supported layers

et al. 2014

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Section: Introductionmentioning

confidence: 99%

Molecular dynamics of itraconazole confined in thin supported layers

et al. 2014

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“…In SCLCPs, a qualitatively similar

behavior is observed for the

relaxation, where an Arrhenius behavior describes the data for

, and a VFT behavior for

[ 42 , 46 , 57 ]. Temperature ratios of

= 1.1–1.3 have been observed in nematic and smectic SCLCPs [ 42 , 46 ], which is close to the ratios observed for our LCE.…”

Section: Resultsmentioning

confidence: 52%

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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“…[19] 2a, 2b: two polyvinyl-ether with cyano-biphenyl groups in the mesogenic unit; [13,14] 3: a polysiloxane copolymer with different side chains differing in the space length; [43] 4a, 4b: polyacrylates with cyanobiphenyl mesogenic groups; [44] 5: polysiloxane with cyano and fluoro groups at the end of the mesogenic unit; [45] 6: polysiloxane with cyano and methyl groups at the end of the mesogenic unit; [46] 7a-7e: five polysiloxanes with alkyl or vinylacetic acid spacer groups; [15] 8: polymethacrylate having (p-alkoxy-phenyl)-benzoate mesogenic groups; [47] LCP1: polysiloxane studied in this work with data extracted from. [19] 2a, 2b: two polyvinyl-ether with cyano-biphenyl groups in the mesogenic unit; [13,14] 3: a polysiloxane copolymer with different side chains differing in the space length; [43] 4a, 4b: polyacrylates with cyanobiphenyl mesogenic groups; [44] 5: polysiloxane with cyano and fluoro groups at the end of the mesogenic unit; [45] 6: polysiloxane with cyano and methyl groups at the end of the mesogenic unit; [46] 7a-7e: five polysiloxanes with alkyl or vinylacetic acid spacer groups; [15] 8: polymethacrylate having (p-alkoxy-phenyl)-benzoate mesogenic groups; [47] LCP1: polysiloxane studied in this work with data extracted from.…”

Section: Discussionmentioning

confidence: 99%

“…[16,47] It was suggested, for example, that from the analysis of the temperature dependence of the characteristic times, both relaxations freeze together at the vicinity of T g , i.e., the characteristic times tend to merge as the temperature decreases down to T g . The cooperative nature of this process allows one to conclude that such motion in a given mesogen should involve translational=rotational motions in other molecular groups, including the spacer directly linked to it or even the polymer backbone.…”

Section: Cooperative Character Of Relaxation Processes In Sclcpmentioning

confidence: 99%

Cooperative Character of the Relaxation Processes in a Side-Chain Liquid Crystalline Polymer

Mano

2003

Journal of Macromolecular Science, Part B

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Side-chain liquid crystalline polymers (SCLCP) are complex materials that exhibit peculiar relaxation processes. Particularly, the assignment of the a-relaxation has been controversial. In this work, its attribution to the segmental dynamics within the backbone is strengthened, despite possibly being highly influenced by special modes of motions within the mesogenic groups in the sidechains. The discussion is based on results obtained by dielectric relaxation spectroscopy, TSDC, DSC, DMA, and TMA. It was found that the motion within the spacers may influence the a-process dynamics, broadening the distribution of relaxation times. The analysis of the fragility locates the a-process in the fragile region of the fragile= strong Angell scale. The d-relaxation of SCLCPs is cooperative and is found to have similar features to the a c -relaxation seen in flexible semicrystalline polymers.

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Comparison of the Molecular Dynamics of a Liquid Crystalline Side Group Polymer Revealed from Temperature Modulated DSC and Dielectric Experiments in the Glass Transition Region

Cited by 28 publications

References 20 publications

Molecular dynamics of itraconazole confined in thin supported layers

Molecular dynamics of itraconazole confined in thin supported layers

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

Cooperative Character of the Relaxation Processes in a Side-Chain Liquid Crystalline Polymer

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