## 2 Results and Discussion
### Characterization of Blm Salt-Based Nanogels and Their Thermo-Responsive Behavior
It can also be seen from Figure 4a-i that BIm-based nanogels are liable to aggregate in the dry state, which results in enlargement of some particles. \begin{table} \begin{tabular}{c c c c c c} \hline \hline
**Entry** & **Monomer and Cross-Linker** & \
\begin{tabular}{c} **Feed Ratio** \\ **(Molar Ratio)****a** \\ \end{tabular} & **D\({}_{\text{h}}\) (nm)** & **PDI** &
\begin{tabular}{c} \(\xi\)**-Potential** \\ **(mV)** \\ \end{tabular} \\ \hline
1 & [C\({}_{6}\)Vlm]Br + EGDMA & 1:1 & precipitated & - & - \\
2 & [C\({}_{6}\)Vlm]Br + EGDMA & 3:1 & 159 & 0.28 & 11.5 \\
3 & [C\({}_{6}\)Vlm]Br + EGDMA & 5:1 & 137 & 0.26 & 12.4 \\
4 & [C\({}_{6}\)Vlm]Br + EGDMA & 10:1 & 103 & 0.43 & 14.1 \\
5 & [C\({}_{6}\)Vlm]Br + EGDMA & 15:1 & 71 & 0.09 & 18.1 \\
6 & [C\({}_{8}\)Vlm]Br + EGDMA & 10:1 & 125 & 0.36 & 13.5 \\
7 & [C\({}_{12}\)Vlm]Br + EGDMA & 10:1 & 148 & 0.45 & 11.9 \\
8 & [C\({}_{6}\)Vlm]Br + DVB & 3:1 & 111 & 0.39 & 14.6 \\
9 & [C\({}_{6}\)Vlm]Br + DVB & 5:1 & 88 & 0.29 & 16.2 \\
10 & [C\({}_{6}\)Vlm]Br + DVB & 10:1 & 47 & 0.33 & 17.1 \\ \hline \hline \end{tabular}   
To put more light on the relationship between the structure of BIm-based monomers and the thermo-response of nanogels, phase transform behavior of BIm-based nanogels were also investigated using turbidimetry and DLS. Figure 1 shows the temperature dependence of turbidity and diameters for 5.0 wt % nanogel solutions in methanol. All these nanogel solutions are blue, opalescent, and translucent above a certain temperature, and suddenly turned cloudy below the above temperature. For example, the transmittance of nanogel solution ([C\(\epsilon\)VIm]Br:EGDMA = 5:1, Figure 1a) is above 80% at the temperature 18 \({}^{\circ}\)C. Nonetheless, the transmittance dropped promptly to below 10% when the temperature decreases to 13 \({}^{\circ}\)C. The discrete transition that occurred within a narrow temperature change indicates that nanogels are thermosensitive particles with an upper critical solution temperature (UCST). The thermosensitive behavior of nanogels was also confirmed by DLS measurements. The hydrodynamic diameter (D\({}_{\text{h}}\)) of nanogels increased rapidly from below 100 nm to micrometer level in the same temperature range. These results reveal that free nanogels were suddenly desolvated to form large aggregates, and precipitated from the solvent below UCST. Though BIm-based nanogels with different constitutions can present thermo-responsive behavior in methanol, marogel cannot be observed in the present system even at lower temperature (-20 \({}^{\circ}\)C). This performance is very different from that of nanogels with short spacer in BIm-based monomer [28]. It is probably because that H-bond interaction between imidazolium ring and methanol is not strong enough in the present system. From Figure 5c,d, It can also be inferred that more [C\(\epsilon\)VIm]Br in the feed will obviously enhance the UCST of the corresponding nanogel when using DVB as the cross-linker. Figure 5: Temperature dependence of transmittance at 500 nm and hydrodynamic diameters (D\({}_{\text{h}}\)) for 5 wt % nanogel in methanol. ((**a**) [C\({}_{6}\)VIm]Br:EGDMA = 5:1; (**b**) [C\({}_{6}\)VIm]Br:EGDMA = 10:1; (**c**) [C\({}_{6}\)VIm]Br: DVB = 3:1; (**d**) [C\({}_{6}\)VIm]Br:DVB = 10:1). FTIR spectra of the as-prepared nanogels with different BIm-based monomers and cross-linkers are indicated in Figure 6. Some typical peaks attributed to BIm-based ILs and EGDMA/DVB copolymers can be clearly recognized, such as aromatic benzene ring (1646, 1500 cm\({}^{-1}\), stretching vibration), aromatic imidazolium ring (1454, 1180 cm\({}^{-1}\) stretching vibration), carbonyl group (1730 cm\({}^{-1}\), stretching vibration), _etc._ Especially, the peak ascribed to the carbon-carbon double bond (1582 cm\({}^{-1}\), stretching vibration) in the vinyl group of the monomers disappeared. These results demonstrate the formation of BIm-based copolymers. Thermo-stabilities of the as-prepared nanogels were measured using thermogravimetric analysis (TGA).