Structure-Property Relationships in the Twist-Bend Liquid Crystal Phase of Odd Members of the CBnCB Homologous Series

We synthesize a series of homologues of CB7CB with different alkyl number n in the linker to investigate the effects of linker length on the properties of the twist-bend phase. We identify the TB phase in the odd members of the CBnCB series for n = 5 – 17 and investigate them primarily with resonant soft x-ray scattering (RSoXS) and non-resonant wide-angle x-ray scattering techniques. Increasing the length of the linker increases the molecular flexibility and decouple the mesogenic arms of the molecules, tending to stabilize the temperature range of the nematic phase while that of the TB phase diminishes. It also dramatically increases the helix pitch and contributes to enhanced structural fluctuations of the helix. We fit the measured helix pitch as a function of temperature for each compound to extract its ground state pitch at low temperature, when fluctuations are frozen out. We find that the ground state helix pitch scales nearly linearly with linker number. Our study not only demonstrates the nanoscale effects of lengthening the chemical linker, but also highlights the surprising importance of fluctuations in the behavior of the twist-bend phase.