Frustrated bilayer smectic phase in main-chain polymers with two different spacers

(Received 10 December 1993, revised 26 January 1994, accepted 18 February 1994)

Abstract
We have studied the structural characteristics of the smectic phases formed by the main-chain type of polymers in which the mesogenic biphenyl moieties are linked by two different odd-numbered aliphatic spacers in a regularly alternate fashion. The first interesting result of this study is that the two different types of layer structures are formed depending on the difference in the lengths of two aliphatic spacers. In the polymers with the two spacers having a small difference in their lengths, the single layer structure is formed as a result of the random mixing of the two different spacers. In contrast, if there is a sufficiently large difference in lengths, the two different spacers participate into different layers and so the smectic phase appears to have a bilayer character. The second interesting result is that the bilayer smectic phase pretends the frustrated structure with the unusual density modulation in the direction parallel to the layer. This frustrated structure has been explained as resulting from a two-dimensional escape of the spontaneous polarization.