Confinement induced relaxations and phase behavior of a nanoconfined columnar ionic liquid crystal

Liquid crystalline mesophases in nanoconfinement exhibit intriguing phase transition behaviors and relaxation dynamics. We investigate the molecular dynamics and electrical conductivity of a linear-shaped guanidinium-based ionic liquid crystal (ILC) confined in self-ordered nanoporous alumina oxide templates of pore diameter 180nm down to 25nm by employing broadband dielectric spectroscopy (BDS) and calorimetry. Calorimetric investigation reveals a complete suppression of the columnar – isotropic transition, while the plastic crystalline – columnar transition temperature decrease with decreasing pore size. Two relaxation modes similar to the bulk sample, the γ, and α₁ relaxation, are observed in the plastic crystalline phase, and a new fast relaxation mode, the α₃ relaxation process emerges in the columnar phase, which is absent for the bulk sample.  The γ relaxation is assigned to the localized fluctuations while the α₁ is due to the segmental dynamics of the alkyl chains. Further possible interpretations for the α₃ process are discussed. For the bulk ILC, a jump of 4 orders of magnitude in the absolute values of DC conductivity occurs at the transition from the plastic crystalline to hexagonal columnar phase, while for the confined ILC, this transition is smooth.