Investigation On The Self-aggregation Of Imidazolium Polymerized Ionic Liquids

Poly (ionic liquid)s (PILs) can form highly ordered microstructure by a self-assembly procedure, and thus are widely used in the preparation of soft template materials, mesoporous materials, high adsorption materials and so on. The ordered structures are closely related to the solution properties of PILs and the microstructure of the PILs aggregates. However, the factors affecting the formation of the ordered PIL assemblies and the spontaneously aggregate mechanism of the PIL chains remain unknown.In this paper, Alkyl imadazolium-based PILs with different alkyl chains and counter-anions were synthesized to explore the self-assembly of PILs. This research focuses on the morphology of the PIL aggregation in its solution, and the factors that have influence on the self-assembly of PILs and thermodynamic potentials (ΔGm(?), ΔHm(?), ΔSm(?)) in the aggregation process.The morphology of the PILs aggregates could be observed via microscopy and transmission electron microscope (TEM). The critical aggregation concentration (CAC) of different PILs in solution was measured by a UV-visible spectrophotometer. According to the obtained CAC and the degree of counterion binding(β), the thermodynamic potentials (ΔGm(?), ΔHm(?), ΔSm(?)) of the aggregation process in solution were calculated. The results show that:1. No matter PILs with Br-or BF4-, when the alkyl chain length is less than C16, the PILs aggregates are not observed orderly layered structure. If the alkyl chain is C16, the aggregation morphology of PILs is "onionlike" multilamellar and the multilamellar structure can maintain a long period of time.2. The size of PILs aggregates depends on the length of alkyl chains, and it has nothing with the paired anion of PILs. The aggregation size in solution increases with the length of alkyl chain increases.3. The structure of PILs and temperature have an effect on critical aggregationconcentration (CAC) of PIL-CnX. The CAC decreases with the alkyl chain length andthe temperature increase.4. The aggregation process of PIL-CnBr, PIL-CnBF4and PIL-CnPF6in solution areaffected by temperature. High temperature was beneficial to PILs self-aggregation.5. The aggregation process of PILs in solution is closely related to the alkyl chainlength and their paired anions. For PIL-CnBr, increasing the alkyl chain length causesthe decrease of GΘm, which was in favorable of the self-aggregation of PILs.However, for PIL-CnBF4and PIL-CnPF6, G Θmgradually increased with the increasein the alkyl chain length, which would weaken the self-aggregation trend.6. The aggregation process of PIL-CnBr, PIL-CnBF4and PIL-CnPF6in solution areentropy-driven.This paper systematically investigated the tail length of alkyl chain, anions andtemprature on the spontaneously aggregate of PILs. And so it was a useful explorationfor understanding the spontaneously aggregation process of PILs in solution and thecontrolled morphology of PILs aggregates. The results we got are significant for thestructure optimization and preparation of soft template materials, mesoporousmaterials and other functional polymer materials.