A highly transparent and ultra-stretchable conductor with stable conductivity during large deformation

Intrinsically stretchable conductors have undergone rapid development in the past few years and a variety of strategies have been established to improve their electro-mechanical properties. However, ranging from electronically to ionically conductive materials, they are usually vulnerable either to large deformation or at high/low temperatures, mainly due to the fact that conductive domains are generally incompatible with neighboring elastic networks. This is a problem that is usually overlooked and remains challenging to address. Here, we introduce synergistic effect between conductive zwitterionic nanochannels and dynamic hydrogen-bonding networks to break the limitations. The conductor is highly transparent (>90% transmittance), ultra-stretchable (>10,000% strain), high-modulus (>2 MPa Young’s modulus), self-healing, and capable of maintaining stable conductivity during large deformation and at different temperatures. Transparent integrated systems are further demonstrated via 3D printing of its precursor and could achieve diverse sensory capabilities towards strain, temperature, humidity, etc., and even recognition of different liquids.

ionogel being squeezed on a plain paper and the leaking IL on the plain paper.

Supplementary Figure 12. Squeezing test of a polyacrylamide/NaCl hydrogel.
Photographs of a polyacrylamide/NaCl hydrogel being squeezed on a plain paper and the leaking water on the plain paper.  A single-point frequency calculation was followed to ensure that the final structure obtained without imaginary frequency. All of the calculations were preformed using the GAUSSIAN 09 package of programs. 3

Supplementary Note 2. Rheological analysis of the 3D printing process
To analyze the rheological behavior of the precursor during 3D printing, we measured stress  2), in which is the volumetric flow rate, is utilized to predict the shear rate γ̇, which is about 40 s −1 . Therefore, the precursor is printed at the viscosity of about 100 Pa s, and its viscosity increases to > 1475 Pa s immediately after extrusion (assuming a shear rate of far below 0.1 s −1 ) which allows for shape retention.

Supplementary Note 3. Comparison of the conductivity measured by different methods
We compare the conductivity measured by different methods. When the conductivity is measured by an LCR meter, the applied voltage is 1 V and the measuring frequency is 1 kHz.
The conductivity ( ) is calculated by, in which is the resistance, and are the materials' geometry factors corresponding to the length and cross-sectional area, respectively. At ambient condition, the calculated S18 conductivity of the conductor with the optimized nanostructure (the molar ratio of the DMAPS, AA and IL is 2:2:1) is 1.2×10 -2 S m -1 . When the conductivity is measured in the same environment by a four electrode method using AC impedance spectroscopy between 0.1 MHz and 1 Hz on a CHI660D electrochemical workstation with potentiostat control, an intersection of the Nyquist plot with the real axis corresponds to resistances of the material. The calculated conductivity is 9.7×10 -3 S m -1 . Therefore, the conductivity of our material measured by different methods is about 10 -2 S m -1 in ambient condition. Unless otherwise stated, we measure the conductivity (resistance) by using the LCR meter for the ease of operation.

Supplementary Note 4. Preparation of electronic and ionic conductors for comparisons
The electronic conductor for the comparison has been reported in our previous work. 5 In brief, the polydimethylsiloxane/graphene composite was prepared by mixing 50 mL

Supplementary Note 5. DSC, DMA results and rheological behaviors of the ionic conductor
There is no melting point observed in DSC curves of this ionic conductor, which indicates there is no free water and the IL in our material does not crystallize even at the temperature S19 as low as -55 o C. Thus the IL is effectively bonded by polymer networks with good environmental stability. Interestingly, there is no glass transition observed in the DSC curves, while a very broad glass transition region is shown in DMA curves, similar to that of a commercial perfluorosulphonic acid ionomer (Nafion), which also shows no glass transition in DSC curves but a quite broad glass transition range in DMA curves. 6 It is worthwhile to note that, the glass transition temperature in DMA curves is determined by the shapes of the curves of storage modulus and the loss modulus. 6,7 There is no plateau region of the storage modulus curve and no peak of the loss modulus curve in our material. They suggest that the polymers' local segmental motion is not completely frozen even at the temperature as low as -55 o C. In another word, there are always different modes of molecular motion that are active in such a broad region. Furthermore, as shown in the rheological results, the polymer networks maintain the solid-like elasticity at -10 and 100 o C, since the storage modulus (G') is always higher than the loss modulus (G''). Therefore, this material is anti-freezing and also stable at high temperature, confirmed by the DSC, DMA and rheology measurements.

Supplementary Note 6. Strain sensing analysis
The capacitive strain sensing is based on the mechanism of parallel-plate capacitance, . Consequently, the capacitance scales as = 0 ( 0 is the initial capacitance).

Supplementary Note 7. Pressure sensing analysis
The capacitive pressure sensing also depends on the dimension change of parallel-plate capacitance. Since the intrinsically stretchable conductor has a much higher modulus than the dielectric layer (the compression modulus of the intrinsically stretchable conductor and VHB layer is about 1000 and 60 kPa, respectively), the capacitance change of the sensory system is mainly determined by the dimension change of the dielectric layer. When the sensory system is compressed by a factor of , the thickness of the dielectric layer is scaled S20 by a factor of 1 − . As a result, the capacitance scales as = 0 suggesting that the intensity of induced voltage directly corresponds to the gradient of ions.