FIGURE 10 a) Photograph of a free-standing FLG film, b) AFM phase image of FLG film, c) photograph of FLG film bended to an angle of ~90o, and d) AFM height images of circled area in c) before and after 100 times bending.
Plenty of affordable, high-quality, yet water-soluble graphene material is highly desirable for many applications, e.g. hydrophilic polymer composites.17 The FLG-P hybrids nicely meet these requirements and were tested for preparation of polymer composite hydrogels. Figure 11a shows a typical PDMAA/FLG hydrogel synthesized by free-radical polymerization of DMAA in the presence of FLG-P-80hybrid. By comparing the weights of hydrogel and its fully dried sample, the water content is determined as 83 wt%. This hydrogel is mechanically tough and flexible. After compressing and then releasing the finger, it can promptly restore its shape and size (Figure 11a). The tensile testing shows that strength, modulus, and elongation at break reach 94 ± 6 kPa, 32 ± 1 kPa, and 288 ± 21%, respectively, corresponding to 225%, 7%, and 202% increments relative to PDMAA hydrogel (Figure 11b). Moreover, this hydrogel is conductive with 1.1 × 10-3 S cm-1 of conductivity, compared with 7.5 × 10-8 S cm-1 for PDMAA hydrogel. This makes it a potential candidate material sustaining the tissue growth, and therein usually lies the demand on electrical stimulation.60