Photoinduced dynamics in a photosensitive side chain polymeric liquid crystal by quasielastic and inelastic neutron scattering (original) (raw)
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Journal de Physique, 1987
On a mesuré, au moyen de la diffusion de neutrons aux petits angles, l'anisotropie de conformation de deux types de polymères cristaux liquides en peigne : un polyméthacrylate et un polyméthylsiloxane, dans leur phase nématique et smectique. On a déterminé les tailles caractéristiques (parallèle et perpendiculaire au directeur) d'une chaîne marquée et leur évolution avec la température Abstract.-The anisotropy of the conformation of two kinds of comblike liquid crystal polymers, a polymethacrylate and a polymethylsiloxane has been measured in the nematic and smectic phases by small angle neutron scattering (SANS). The global sizes (parallel and perpendicular to the director) of one labelled chain and their temperature dependence have been determined. Tome 48 N° 7 JUILLET 1987
Photoinduced Molecular Reorientation and Relaxation in a Liquid Crystalline Polymer
Molecular Crystals and Liquid Crystals, 2002
In this paper we present a study of photoinduced e ects, including molecular relaxation in a side chain liquid crystalline polymer. In particular, we have studied relaxation phenomena using Ellipsometry and Photoinduced Birefringence in pump-probe experiments, which were carried out as a function of temperature, optical pump intensity and sample preparation and history. Two speci c areas were investigated in detail: the frustration effect of the trans-cis photoisomerization transition on the nematic phase, and hence the photoinduced isothermal transition from perturbed nematic to a totally frustrated (isotropic) phase; and the approach of the glass transition, in such a fragile polymeric glass as the one we studied.
Journal of Physics B Atomic and Molecular Physics
We have simultaneously measured, for the first time, the extension of the polymer backbone of a side-chain liquid crystalline polymer and the intensity of the 001 Bragg reflection, which gives the smectic order parameter Psi\PsiPsi as a function of temperature in the smectic phase. We have qualitatively demonstrated that the more the smectic phase is ordered, the more the polymer backbone is localized between the mesogenic layers. It is shown that the Landau theory allows us to relate the radius of gyration parallel to the magnetic field of the polymer backbone to the smectic order parameter. We also show that the Renz-Warner theory is suitable at low temperatures.
The Frozen State in the Liquid Phase of Side-Chain Liquid-Crystal Polymers
Physical Review Letters, 2006
Quenched isotropic melts of side-chain liquid-crystal polymers reveal surprisingly an anisotropic polymer conformation. This small-angle neutron-scattering (SANS) result is consistent with the identification of a macroscopic, solidlike response in the isotropic phase. Both experiments (rheology and SANS) indicate that the polymer system appears frozen on millimeter length scales and at the time scales of the observation. This result implies that the flow behavior is not the terminal behavior and that crosslinks or entanglements are not a necessary condition to provide elasticity in melts.
Pressure Induced Mesophases in Side-Chain Polymer Liquid Crystal Revealed by Neutron Diffraction
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 2001
ABSTRACT We report here pressure studies on a side-chain liquid crystalline polymer which exhibits a reentrant nematic phase at atmospheric pressure. It reveals that the two nematic transitions behave differently.The N-SAd transition is shifted towards higher transition temperatures whereas the SAd-NRe transition remains invariant with increasing pressure. In the smectic phase, a significant increase of the order parameter and of the correlation length of the smectic layers is observed. The results are obtained using a pressure cell specifically designed for neutron diffraction.
Side chain mesomorphic polymers : studies of labelled backbones by neutron scattering
Journal de Physique Lettres, 1985
2014 Des polymères mésomorphes en peigne sont étudiés dans les phases isotrope, nématique et smectique. Les échantillons sont formés de mélanges de polyméthacrylates cristaux liquides dont les squelettes sont deutériés ou hydrogénés. Ils sont étudiés par diffraction et diffusion de neutrons aux petits angles. Les résultats montrent en particulier que dans la phase smectique alignée : i) le squelette présente une forte anisotropie, il est confiné dans une couche smectique. ii) Le marquage du squelette fait apparaitre un ordre local en bicouche.
Interest of neutron scattering for the investigation of liquid-crystalline polymers
Acta Physica Hungarica, 1994
Small-Angle Neutron Scattering is the unique method which allows the determination of the polymer conformation in the bulk. This method has been applied to several kinds of liquid crystalline polymers. We report here general results obtained on side-chain liquid-crystal polymer, main-chain liquid-crystal polymer and finally combined liquid-crystal polymers. It is shown that the polymer conformation is largely dependent on the insertion site of the liquid crystal molecule and on the structure of the mesophase.
Vibrational Spectroscopy of Polymer Liquid Crystals
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1994
In this paper we review results of the application of Raman scattering and infrared spectroscopy to the study of molecular dynamics in liquid crystalline polymers. In particular we report on the study of molecular ordering and reorientation and illustrate the results we have obtained in a newly synthesized class of side-chain liquid crystalline polymers belonging to the polyacrylate family. The physical basis and experimental methods necessary for the application of these techniques are also discussed in this paper.
Neutron scattering and the glass transition in polymers – present status and future opportunities
Journal of Non-Crystalline Solids, 2001
We present results obtained by the exploration of molecular motions by neutron scattering and outline future opportunities resulting from methodological progress in high-resolution neutron spectroscopy. Starting on methododical grounds, we will commence with possible future developments in neutron spin echo spectroscopy (NSE), the prime technique for the observation of molecular processes in the nanosecond domain. After describing the scope of neutron scattering for experiments on glass-forming materials, we will present measurements of the self-correlation function, which include the b-relaxation in polyisobutylene, and address the problem of the heterogeneity of the a-process. Thereafter, we deal with dierent aspects of the pair correlation function, starting from coherent scattering experiments on polybutadiene, where the choice of the momentum transfer is selective for the observation of the a-or b-relaxation. Then, we emphasize results on the structural relaxation obtained for the dierent polymers at the ®rst structure factor peak. Finally, by example, we will address the capability of neutron scattering, to deal with motions in polymer blends, where by judicious labeling the dynamics of the dierent components can be observed separately. Ó 2001 Published by Elsevier Science B.V. (M. Monkenbusch), wapar-mea@sc.ehu.es (A. Arbe), wapcolej@sc.ehu.es (J. Colmenero). 0022-3093/01/$ -see front matter Ó 2001 Published by Elsevier Science B.V. PII: S 0 0 2 2 -3 0 9 3 ( 0 1 ) 0 0 6 3 1 -7
Small Angle Neutron Scattering (Sans) Studies on “Side-On Fixed” Liquid Crystal Polymers
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1994
The kinetics of aggregation of two pyromellitamide gelators, tetrabutyl-(C4) and tetrahexyl-pyromellitamide (C6), in deuterated cyclohexane has been investigated by small angle neutron scattering (SANS) for up to 6 days. The purpose of this study was to improve our understanding of how self-assembled gels are formed. Short-term (< 3 h) time scales revealed multiple phases with the data for the tetrabutylpyromellitamide C4, indicating one-dimensional stacking and aggregation corresponding to a multifiber braided cluster arrangement that is about 35 Å in diameter. The corresponding tetrahexylpyromellitamide C6 data suggest that the C6 also forms one-dimensional stacks but that these aggregate to a thicker multifiber braided cluster that has a diameter of about 62 Å. Over a longer period of time, the radius, persistence length, and contour length all continue to increase in 6 days after cooling. These data suggest that structural changes in self-assembled gels occur over a period exceeding several days and that fairly subtle changes in the structure (e.g., tail-length) can influence the packing of molecules in self-assembled gels on the singleto-few fiber bundle stage.