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See detailDifferences between smectic homo- and copolysiloxanes as a consequence of microphase separation
Rössle, Martin; Braun, L.; Schollmeyer, D. et al

in Liquid Crystals (2005), 32(5), 533-538

This paper compares smectic phases formed from LC-homo- and LC-co-polysiloxanes. In the homopolysiloxane, each repeating unit of the polymer chain is substituted with a mesogen, whereas in the ... [more ▼]

This paper compares smectic phases formed from LC-homo- and LC-co-polysiloxanes. In the homopolysiloxane, each repeating unit of the polymer chain is substituted with a mesogen, whereas in the copolysiloxanes mesogenic repeating units are separated by dimethylsiloxane units. Despite a rather similiar phase sequence of the homo- and co-polysiloxanes—higher ordered smectic, smectic C* (SmC*), smectic A (SmA) and isotropic—the nature of their phases differs strongly. For the copolymers the phase transition SmC* to SmA is second order and of the ‘de Vries’ type with a very small thickness change of the smectic layers. Inside the SmA phase, however, the smectic thickness decreases strongly on approaching the isotropic phase. For the homopolymer the phase transition SmC* to SmA is first order with a significant thickness change, indicating that this phase is not of the ‘de Vries’ type. This difference in the nature of the smectic phases is probably a consequence of microphase separation in the copolymer, which facilitates a loss of the tilt angle correlation between different smectic layers. This has consequences for the mechanical properties of LC- elastomers formed from homo- and co-polymers. For the elastomers from homopolymers the smectic layer compression seems to be rather high, while it seems to be rather small for the copolymers. [less ▲]

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See detailFerroelectric polysiloxane liquid crystals with ‘de vries’-type smectic a* -smectic c* transitions
Rössle, Martin; Zentel, Rudolf; Lagerwall, Jan UL et al

in Liquid Crystals (2004), 31(6), 883-887

We report preliminary results of optical and small angle X-ray scattering (SAXS) experiments on the smectic A*2smectic C* transition in two ferroelectric liquid crystalline polysiloxanes. Although the ... [more ▼]

We report preliminary results of optical and small angle X-ray scattering (SAXS) experiments on the smectic A*2smectic C* transition in two ferroelectric liquid crystalline polysiloxanes. Although the optical tilt angle in the SmC* phases reaches values up to 30‡, temperature-dependent SAXS measurements clearly reveal that the smectic layer spacing is basically conserved during the A*–C* transition as well as in the subsequent C* phase. Connected with the A*–C* transition we further observed a significant increase in bire- fringence, hence reflecting an increase of orientational order. The practical absence of layer shrinkage and the enhanced orientational ordering are consistent with the de Vries diffuse cone model of smectic A2smectic C transitions. [less ▲]

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