Enhancing Electroresponsive Electrorheological Effect and Temperature Dependence of Poly(ionic liquid) Particles by Hard Core Confinement

Abstract

Monodisperse core−shell-structured SiO 2 @ poly(ionic liquid) (SiO 2 @PIL) particles are prepared by the polymerization of ionic liquid monomer on the surface of methacryloxypropyltrimethoxysilane-modified SiO 2 particles. The electroresponsive electrorheological (ER) effect of SiO 2 @ PIL particles when dispersed in insulating carrier liquid is investigated and compared with that of pure poly(ionic liquid) (PIL) particles based on temperature-modulated rheology under electric fields. It is demonstrated that hard SiO 2 core not only enhances the ER effect of PIL particles but also improves the temperature dependence of ER effect. By dielectric spectroscopy analysis, the mechanism behind the property enhancement was discussed. It indicates that the hard SiO 2 core can not only increase the interfacial polarization strength of SiO 2 @PIL particles by core−shell architecture but also restrain the segment relaxation or softening of the PIL shell and influence the ion dynamics above the calorimetric glass transition of PILs by the so called "substrate confinement effect", and this should be responsible for the enhanced electroresponsive ER effect and temperature stability of the SiO 2 @PIL particles.

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

“…When a polymer is prepared on a inorganic substrate surface (e.g., SiO 2 ), the strong interfacial interaction between the polymer and the inorganics will affect the T g of the polymer by changing the stereoregularity of the polymer [ 94 ]. That is why core-shell particles with a SiO 2 core and PIL shell were designed for the above issue [ 95 ]. Figure 8 is the schematic preparation process of SiO 2 @P[MTMA][TFSI] core-shell particles.…”

“…Other advantages achieved are the enhanced ER effect and broad working temperature range as well. Lei et al [ 95 ] chose SiO 2 particles as hard core and prepared SiO 2 @P[MTMA][TFSI] particles with core-shell structure. Because of the strong interaction between PILs shell and SiO 2 core, the segmented movement of PILs is limited, leading to the increase in T g of the PILs.…”

“…Moreover, the plasticizing effect of polyatomic fluorinated counter ions ([TFSI]¯) reduces the T g of PILs, which decreases the thermal stability of the PILs-based ER fluids. In order to improve the thermal stability of the ER fluids, PILs encapsulated nano-SiO 2 composite particles and SiO 2 @P[MTMA][TFSI] core-shell particles were designed and synthesized [ 95 , 101 ], which limit the movement of chain segments and the ionic transport of PILs. After analyzing dielectric properties of the SiO 2 @P[MTMA][TFSI] core-shell particles, it is found that the hard SiO 2 core not only increases the dielectric strength of the core-shell particles but also restrains the segment relaxation of the P[MTMA][TFSI] shell.…”

“…Upon the study of the Arrhenius dependence of the PILs-based ER fluids, it is indicated that the ion motions in PILs or its composites are from the thermal diffusion, and not coupled with the chain segment below T g of the PILs. The situation is much different when temperature is higher than T g , the activation of segment relaxation drives λ −1 to depart from the Arrhenius line [ 95 ].…”

“… Schematic preparation of SiO 2 @P[MTMA][TFSI] core-shell particles, reprinted with permission from [ 95 ]. Copyright ACS, 2018.…”