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