Side Chain Length-Dependent Dynamics and Conductivity in Self-Assembled Ion Channels

Abstract

We study the molecular mobility and electrical conductivity of a homologous series of linear shaped columnar ionic liquid crystals ILCn, (n = 8, 10, 12, 14, 16) using broadband dielectric spectroscopy (BDS), specific heat spectroscopy (SHS), and X-ray scattering. We aim to understand how the alkyl chain length influences the dynamics and electric conductivity in this system. Two dielectrically active relaxation modes are observed, the γ and the α core process, that correspond to the localized fluctuations of the alkyl chains and cooperative motions of the aromatic core in the columns, respectively. Both the γ relaxation and the α core process slow down with increasing alkyl chain length. SHS reveals one relaxation process, the α alkyl process that has a similar temperature dependence as that of the α core process for ILC12, 14, and 16 but shifts to higher temperature for ILC8 and 10. For ILC12, 14, and 16, the absolute values of DC conductivity increase by 4 orders of magnitude at the transition from the plastic crystalline to hexagonal columnar phase. For ILC8 and 10, the DC conductivity behavior is similar to ionic liquids, where the conductivity is coupled with structural relaxation. Small-angle X-ray investigations reveal that both the intercolumnar distance and the disorder coherence length increase with alkyl chain length; conversely, the DC conductivity decreases monotonically.

Confinement-Suppressed Phase Transition and Dynamic Self-Assembly of Ionic Superdiscs in Ordered Nanochannels: Implications for Nanoscale Applications

“…Assigning the peak in the isotropic phase to columns, the peak broadening indicates a higher disorder in the columns in the isotropic state compared to the hexagonal columnar phase. 14,37 The estimated transition temperature coincides with the crossover temperature observed for α 2 relaxation (410 K). As discussed above, the higher disorder in the columns may also ease the dynamic selfassembly of the superdiscs (α 2 relaxation).…”

“…Investigations on guanidinium-based columnar ILCs in the bulk state include, the influence of the cation headgroup as well as the length of the alkyl chain concerning the stability of the mesophase, including charge transport, . Slight variations in the molecular structure directly alter the macroscopic properties of the system.…”

“…On the one hand, ILCs with a cyclic cation headgroup have a higher DC conductivity and faster molecular dynamics compared to their acyclic counterpart . On the other hand, a systematic variation of the length of the alkyl chain in ILCs revealed that ILCs with alkyl side chain lengths of 8 and 10 behave more like ionic liquids with a narrow mesophase window, while the long chain ILCs (alkyl side chain lengths 12, 14, and 16) show a broad mesophase range but a reduced electrical conductivity …”

“…12 Investigations on guanidinium-based columnar ILCs in the bulk state include, the influence of the cation headgroup as well as the length of the alkyl chain concerning the stability of the mesophase, including charge transport, 13 . 14 Slight variations in the molecular structure directly alter the macroscopic properties of the system. On the one hand, ILCs with a cyclic cation headgroup have a higher DC conductivity and faster molecular dynamics compared to their acyclic counterpart.…”

Does thermotropic liquid crystalline self-assembly control biological activity in amphiphilic amino acids? – tyrosine ILCs as a case study

“…We surmised that dipole interactions of the guanidinium salts not only contributed to their liquid crystalline self-assembly and phase behavior, [92][93][94][95] but might also affect their biological activities 96 and thus selected members were studied regarding their dipole moment. The dipole moments of the compounds 3,4,5-C 10 TyrC 14 Cl, BzTyrC 12 Cl and 3,4,5-C 10 TyrC 12 Cl were experimentally determined by dielectric measurements of the compounds in toluene solution.…”