In order to develop novel amphibian-inspired conductive ionogels for multifunctional biosensing, the design strategy adopted in this study was shown in
Scheme 1. We first prepared hydrophobic ionic liquid (IL) [N
4111]
+ [TFSI]
− by mixing cations and anions [
43]. The
1H NMR spectroscopy provided evidence for the successful preparation of [N
4111]
+ [TFSI]
− (Fig. S1 in Supporting information). Significantly, we selected IL and the hydrophobic monomer HFBA with C-F to construct the ionogels, because the high electronegativity of fluorine and the strong electrostatic properties of the C-F bonds made them poor hydrogen donors and acceptors [
44]. This interaction would avoid the interference of water molecules, therefore endowing unique hydrophobicity for the ionogel and environmental stability. Meanwhile, the monomer DMAA effectively was designed to modulate the mechanical properties of the ionogel [
45,
46]. The HDI ionogel formation process could be visualized in
Fig. 1A, and the internal supramolecular interactions in Fig. S2 (Supporting information). The mixture of HFBA and DMAA presented a light yellow liquid, transparent [N
4111]
+ [TFSI]
−, photoinitiator and crosslinker were introduced into the solution. Subsequently, the above homogeneous and transparent precursor solution was transferred into a silica gel mold for photopolymerization under UV light. According to
Fig. 1B, the average transmittance of the yellowish ionogel in the visible region (400-800 nm) was 87%. This good transparency confirmed the compatibility of [N
4111]
+ [TFSI]
− and the hydrophilic and hydrophobic chain segments of the copolymer resulting in a homogeneous dispersion system. X-ray diffraction (XRD) spectral analysis revealed no strong scattering peaks (Fig. S3 in Supporting information), indicating that the ionogels were homogeneously dispersed structures without phase separation at the nanoscale [
47]. The morphology and elemental distribution of the ionogels were analyzed by scanning electron microscopy (SEM) and energy spectrometry (EDS) (
Fig. 1C). The X-ray photoelectron spectroscopy (XPS) was consistent with EDS results (
Fig. 1D). The N 1s spectrum in XPS could be deconvoluted into two peaks centered at 402.2 and 398.9 eV, corresponding to the N atoms in N
+ of IL [N
4111]
+ cation and S-N-S of IL [TFSI]
− anions, respectively (Fig. S4 in Supporting information). Significantly, high-resolution XPS can distinguish different environments of fluorine and carbon atoms, which can provide insight into the interactions between the copolymer and [N
4111]
+ [TFSI]
−. By comparing the F-atom binding energy of HDI with copolymer P(HFBA-
co-DMAA) it was found that the binding energy shifted from 688.2 eV to 688.4 eV in
Fig. 1E. Meanwhile, a comparison of the C-atom binding energy revealed that the binding energy of the HDI group was increased by 1.9 eV and the electron cloud density was decreased (Fig. S5 in Supporting information). These results indicated that the HFBA fragments in the polymer network had ion-dipole interactions with the [N
4111]
+ cations of the IL [
48]. Furthermore, the existence of ion-dipole interactions could also be demonstrated by Fourier transform infrared (FTIR) spectroscopy. The addition of [N
4111]
+ [TFSI]
− caused the C-F stretching vibration and S-N-S antisymmetric stretching vibration of the HDI to higher wavenumbers (Fig. S6 in Supporting information). This indicated that ion-dipole interactions led to cation attraction to the [TFSI]
− anion, cation coulomb force was weakened and S-N-S force increased [
44]. Therefore, the ion-dipole interactions effectively enhanced the compatibility of IL with the chain segment in ionogel, and also prevented the IL leakage, providing excellent stability for the ionogel.