Gyroid Labyrinth of Supertwisted Double Helices in a Liquid Crystal Polymer

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Abstract
A liquid crystal (LC) polymethylsiloxane (PMS) with rod‐like aromatic side‐groups attached via an alkylene spacer and bearing three n‐dodecyl end‐tails is found to form an unusual cubic structure. In a normal LC double gyroid (DG), the two chiral subspaces, one each side of the G‐surface, are occupied by one network each. Here each such network is split into two aromatic strands that wind around the central polysiloxane bundle, forming a double helix, resulting in a four‐network gyroid (4NG). While in previous normal LC DGs the network twist was assumed to follow that of the subspace, in 4NG the twist sense of the double‐helix is opposite to that of the subspace., i.e., while a right‐handed subspace twists by +70.5° between junctions, the double‐helix “supertwists” by −109.5°, and the opposite is true for the left‐handed subspace. Detailed analysis by X‐ray diffraction, DSC, and depolarized fluorescence (DF) shows a gradual but significant reversible change in the degree of mixing between the aromatic side groups and the polysiloxane backbones at 120 °C–130 °C in 4NG. Also, a significant increase in the system mobility starts only at ∼40 °C above the melting point, indicating persistence of local double‐helical segments even in the melt.
Funding Information
  • National Natural Science Foundation of China (92156013, 92356306, 52373022)
  • Engineering and Physical Sciences Research Council (EP/T003294)

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