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Liquid Crystals and their Application
Russian Journal

Zhidkie kristally i ikh prakticheskoe ispol'zovanie

Жидкие кристаллы и их практическое использование

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Rus Eng

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Zhidk. krist. ikh prakt. ispol'z. = Liq. Cryst. and their Appl., 2017, 17 (3), 83—92.
DOI: 10.18083/LCAppl.2017.3.83





Structure of Liquid Crustal Poly(Propylene Imine) Dendrimers of the Lowest Generations by X-Ray Analysis



T. V. Pashkova1,2, A. I. Alexandrov1, M. S. Gruzdev3, A. V. Pyatunin1

Author affiliations
1Ivanovo State University,
37/7 Ermak St., Ivanovo, 153025, Russia
E-mail: pashtavi@yandex.ru
2Ivanovo Fire Rescue Academy of State Firefighting Service of Ministry of Russian Federation,
33 Stroiteley Ave., Ivanovo, 153040, Russia
3G. A..Krestov Institute of Solutions Chemistry Russian Academy of Sciences,
1 Academic St., Ivanovo, 153045, Russia

Abstract
Liquid crystal poly(propylene imine) dendrimers of zero (D0) and first (D1) generations exposed to the magnetic field influence were investigated by X-ray diffraction method. Analysis of diffraction patterns was carried out with the use of the paracrystal model of Hosemann and the cluster model of Fonk. Structural simulation and diffraction calculations on the models were used for determining of the layer structure parameters of the dendrimers. Temperature behavior of the structural parameters was considered in the interval from room temperature to isotropic melting temperature.
It was determined that only the dendrimer of zero generation can be oriented by magnetic field. This dendrimer forms crystalline phase, but at the same time D0 is capable to partial vitrifying preserving the structure of smectic C phase. D0 has orthorhombic crystalline lattice with parameters: а = 39,2 Å, b = 9,76 Å, c = 14,25 Å. There are four molecules in the elementary cell. The calculated specific density is 1,09 g/sm3. The space group of a symmetry is P21212. Increase of generation number results in more advanced liquid crystal polymorphism. D1 forms two smectic phases: SmC and SmF. D1 does not crystallize, but vitrifies preserving the structure of smectic F phase. Structural models confirmed by diffraction analysis suppose an elongated molecular conformation in all phase states of both D0 and D1. The phase transformations of the dendrimers look like: Cr → 159 °С → SmC → 274 °С → Iso of D0 and G → 55–66 °С → SmF → 108 °С → SmC → 274 °С → Iso of D1. Temperature dependences of structural parameters of the dendrimers near the phase transitions Cr → SmC of D0 and SmF → SmC of D1 contain features of a two-phase behaviour of the dendrimers (this effect is less expressed for D1).

Keywords: liquid crystalline dendrimers, X-ray diffraction, structure – phase transitions





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