Reference : Differences between smectic homo- and copolysiloxanes as a consequence of microphase ...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Chemistry
Differences between smectic homo- and copolysiloxanes as a consequence of microphase separation
Rössle, Martin [> >]
Braun, L. [> >]
Schollmeyer, D. [> >]
Zentel, R. [> >]
Lagerwall, Jan mailto [Universität Stuttgart]
Giesselmann, Frank [> >]
Stannarius, Ralf [> >]
Liquid Crystals
Taylor & Francis Ltd
Yes (verified by ORBilu)
[en] 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.

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