Smectic elastomers, "single crystal

Nishikawa E, Finkelmann H. 1999. Smectic A liquid single crystal elastomers strain induced break down of smectic layers. Macromol Chem Phys 200 312 322. 

Most experiments on LC elastomers have so far used single crystal elastomers made via the two-step crosslinking process, which involves stretching in the LC state. There is increasing evidence that this situation represents a special thermodynamic state - smectic elastomers made in such a way are well aligned but their layer positions are frustrated due to the random crosslink distribution. Evidently, there is room for experiments on nematic and smectic elastomer samples oriented in different ways, for example by photo-crosslinking. In such a way, any memory of the aligning procedure imprinted in the samples will be avoided (at least partially) and new features of phases and phase transitions could be revealed. 

The following protocols (6-10) describe the synthesis of some cholesterol-based acrylates and their photopolymerization in an aligned cholesteric phase. The protocols utilize a modification of a system previously described by Shannon. 5 6 ip ie absence of a diacrylate comonomer, the cholesteric phase produced initially on copolymerization is not stable and reverts to a smectic phase on a single cycle of heating and cooling. In the presence of the diacrylate the first-formed phase is stable. This is one example of how crosslinking can stabilise the liquid crystal phase in liquid crystalline elastomers, others include, the so-called, polymer-stabilized liquid crystals and those described in the later protocols. 

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