Nanoparticle-controlled glassy dynamics in nematogen-based nanocolloids

Drozd-Rzoska, Aleksandra; Starzonek, Szymon; Rzoska, Sylwester J.; Kralj, Samo

doi:10.1103/physreve.99.052703

Cited by 17 publications

(16 citation statements)

References 49 publications

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“…The latter makes the impact of ionic-dopants, which can cause the parasitic heating effect, negligible. This report is based on the results of in-deep re-analyzed earlier findings of the author [21,33,38,39] and new measurements. The latter is related mainly to NDE studies and results presented in Figure 1 as well as in the Appendix A.…”

Section: Methodsmentioning

confidence: 80%

“…In the opinion of the author, the link of this phenomenon to the growing impact of topological defects distorting the uniaxial arrangement can be indicated [42]. Such a possibility can show experimental studies and related modeling for 5CB + nanoparticles composites [20,21].…”

Section: Resultsmentioning

confidence: 97%

“…Generally, no pretransitional behavior near the nematic-solid phase transition is expected. [1][2][3][4][5][6][7][8] Notwithstanding, there is a limited evidence of such behavior, in 2-cyano-4-pentylbiphenyl 4-(trans-4-pentylcyclohexyl) benzoate (the LC compound with the transverse location of the permanent dipole moment), [19] or 5CB and BaTiO 3 nanoparticles composites [20,21], for instance.…”

Section: Introductionmentioning

confidence: 99%

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‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

Drozd-Rzoska

2020

Crystals

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Results of dielectric studies in the nematic and isotropic liquid phases of pentylcyanobiphenyl (5CB), a model rod-like liquid crystalline material, are shown. They are based on the discussion of the evolution of dielectric constant ( ε ), its changes under the strong electric field (nonlinear dielectric effect, NDE), and finally, the primary relaxation time. It is shown that changes in ε T and NDE are entirely dominated by the impact of pretransitional fluctuations (pre-nematic and pre-isotropic, respectively) which are associated with the weakly discontinuous character of the isotropic–nematic phase transition. This influence also extends for the low-frequency, ionic species dominated, region. Notable, that the derivative-based and distortions sensitive analysis revealed the tricritical nature of the I-N transition. Although the glass transition in 5CB occurs in the deeply supercooled state at T g ≈ − 68 ° C , the dynamics (changes of the primary relaxation time) follow a previtreous pattern both in the isotropic and in the nematic phase. Finally, the discussion of the ’molecular’ vs. ‘quasi-critical’ characterizations of the isotropic and nematic phases is presented. It shows the evident prevalence of the ‘quasi-critical-picture’, which offers the consistent temperature parameterization in the total tested temperature range.

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Section: Methodsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

Drozd-Rzoska

2020

Crystals

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“…For LC-based materials, a number of studies have investigated the coupling between ion conduction and structural relaxation [ 15 , 17 , 76 ]. In 5CB, in the isotropic phase on the approach of

Section: Resultsmentioning

confidence: 99%

“…In 5CB, in the isotropic phase on the approach of

, a strong deviation from a Walden-plot gradient of 1 was observed, indicating significant decoupling, which was explained as due to the presence of pre-transitional nematic fluctuations [ 16 ]. The addition of nanoparticles to the isotropic phase of 5CB was shown to reduce the decoupling between DC-conductivity and the

relaxation and the behavior was attributed to the nanoparticle-induced disruption of pre-transitional nematic fluctuations in the isotropic phase [ 76 ]. The nematic phase shows a distribution of nematic domains with slightly varying order parameters and orientations throughout the sample, and is therefore likely to be more dynamically heterogeneous than the isotropic phase, which contains only pre-transitional nematic effects.…”

Section: Resultsmentioning

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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Review of Theoretical Advances of Nanomaterials and Nematic Liquid Crystal Composites

Mukherjee

2024

Braz J Phys

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Nanoparticle-controlled glassy dynamics in nematogen-based nanocolloids

Cited by 17 publications

References 49 publications

‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

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

Review of Theoretical Advances of Nanomaterials and Nematic Liquid Crystal Composites

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