The Electric Field Responses of Inorganic Ionogels and Poly(ionic liquid)s

Abstract

Ionic liquids (ILs) are a class of pure ions with melting points lower than 100 °C. They are getting more and more attention because of their high thermal stability, high ionic conductivity and dielectric properties. The unique dielectric properties aroused by the ion motion of ILs makes ILs-contained inorganics or organics responsive to electric field and have great application potential in smart electrorheological (ER) fluids which can be used as the electro-mechanical interface in engineering devices. In this review, we summarized the recent work of various kinds of ILs-contained inorganic ionogels and poly(ionic liquid)s (PILs) as ER materials including their synthesis methods, ER responses and dielectric analysis. The aim of this work is to highlight the advantage of ILs in the synthesis of dielectric materials and their effects in improving ER responses of the materials in a wide temperature range. It is expected to provide valuable suggestions for the development of ILs-contained inorganics and PILs as electric field responsive materials.

Keywords: dielectric spectra; electrorheological fluid; ionic liquid; ionogel; poly (ionic liquid).

Figure 1

The arrangement structure of the dispersed particles in an ER fluid before (a) and after (b) the application of an external electric field.

Figure 2

Chemical structures of cations and anions of some ILs.

Figure 3

(a) SEM image of SiO₂-based ionogels (SiO₂/IL201), reprinted with permission from [46]. Copyright RSC, 2011. (b) TEM image of SiO₂-based ionogels (IL-ORMOSIL 1), reprinted with permission from [47]. Copyright Elsevier, 2017.

Figure 4

Chemical structures of cationic and anionic IL monomers for PILs: (A) [DADMA]⁺; (B) [VIm]⁺ [BETA]⁺; (C) [CnVIm]⁺; (D) [VBTRA]⁺; (E) [STFSI]⁻; (F) [CnDVIM]²⁺.

Figure 5

The microwave-assisted synthesis process of P[MTMA][TFSI], reprinted with permission from [91]. Copyright RSC, 2014.

Figure 6

(a) SEM image of P[MTMA][TFSI] particles, reprinted with permission from [91]. Copyright RSC, 2014. (b) SEM image of P[VIm][TFSI] particles, reprinted with permission from [92]. Copyright Elsevier, 2019.

Figure 7

Schematic diagram of chain formation of uncross-linked (a,b) and cross-linked (c,d) PILs particles at low and high temperatures, reprinted with permission from [93]. Copyright RSC, 2017.

Figure 8

Schematic preparation of SiO₂@P[MTMA][TFSI] core-shell particles, reprinted with permission from [95]. Copyright ACS, 2018.

Figure 9

Schematic diagram of fabrication of GO/PPy/PIL nanosheets, reprinted with permission from [115]. Copyright Elsevier, 2018.

Figure 10

Temperature dependence of static yield stress (τ_s) (A) and Δτ (B) for P[C₂DVIM]X ER fluids (φ = 20 vol%). The electric field strength is 3 kV/mm and shear rate is 630 s⁻¹. Reprinted with permission form [125]. Copyright Elsevier, 2019.

Figure 11

Chemical structure of anionic PILs with different geometry of counter cations, reprinted with permission from [126]. Copyright Elsevier, 2020.

Figure 12

Dependence of relative permittivity (a) and conductivity (b) on frequency for the silica, silica/IL1, and silica/IL2 suspensions, reprinted with permission from [45]. Copyright Elsevier, 2013.

Figure 13

Dielectric spectra of the suspensions of P[MTMA][TFSI] microspheres (a) P[MTMA][TFSI]@PANI (thin) microspheres (b) and P[MTMA][TFSI]@PANI (thick) microspheres (c) (φ = 20 vol%, T = 23 °C), reprinted with permission from [110]. Copyright John Wiley & Sons, 2018.

Figure 14

(a) Temperature dependence of the relaxation time of the ER fluids based on of P[VBTMA][TFSI] and cross-linked P[VBTMA][TFSI] particles with different weight ratios of the cross-linker (a), reprinted with permission from [93]. Copyright RSC, 2017. (b) The self-crosslinked PILs with different alkyl space length, reprinted with permission from [138]. Copyright Elsevier 2019. The solid lines in (a,b) are fitted by the Arrhenius equation.