Phenyl-dependent self-assembly of imidazolium [FeCl₄] ionic liquids for tunable ice recrystallization inhibition

Ice recrystallization inhibition (IRI) is important for controlling ice growth in frozen soft matter systems, but how molecular structure regulates supramolecular assembly and IRI activity has not yet been fully elucidated. Herein, three [FeCl₄]^--based imidazolium ionic liquids bearing zero, one, and two phenylene linkers, denoted as 0ph-imi[FeCl₄], 1ph-imi[FeCl₄], and 2ph-imi[FeCl₄], were synthesized to investigate phenyl-dependent self-assembly and ice recrystallization behavior. All three ionic liquids formed spindle-shaped nanosheets in aqueous solution. With increasing phenyl-ring number, the assemblies exhibited enhanced internal ordering, while the longitudinal dimension decreased for 2ph-imi[FeCl₄] to 99 ± 11 nm, compared with 224 ± 26 nm and 233 ± 32 nm for 0ph-imi[FeCl₄] and 1ph-imi[FeCl₄], respectively. At 1.28 mM, the normalized mean largest grain size decreased from 93.3 ± 10.3% for 0ph-imi[FeCl₄] to 85.7 ± 9.0% for 1ph-imi[FeCl₄] and 61.0 ± 6.7% for 2ph-imi[FeCl₄], indicating enhanced IRI activity with increasing phenyl-ring number. These results suggest that the phenyl-dependent IRI activity is associated with the combined contributions of assembly dimensions, internal ordering, and possible ice-surface interactions.