FIGURE 9 Raman spectra of a) graphite, b) FLG-P-80hybrid, and c) FLG-P-20 hybrid.
Although polymer molecules residing on the FLG surface may be unwanted
for some uses, they are really helpful for preparation of the flexible
FLG films. Figure 10a shows a typical one prepared by vacuum filtration
of aqueous dispersion of FLG-P-80 hybrid (0.5 mg
mL-1) over a 25 nm hydrophilic membrane followed by
drying in an oven at 70 oC. AFM analysis (Figure 10b)
reveals that FLG sheets involved in the film are aligned parallel to the
film plane. The obtained free-standing film (47 mm-diameter and 28
μm-thick) is robust and can be bent to an angle of
~90o without breaking (Figure 10c).
Even after 100 bendings, no cracks or delamination are observed by naked
eyes. In microscopic scale, no discernible morphological changes occur
before and after bending tests; average surface roughness only slightly
increases from 151 to 160 nm (Figure 10d). As a sharp contrast, the film
prepared from shear-exfoliated FLG in NMP or aqueous solution of SDBS
breaks under the same bending condition. The toughening effect of
VIB-co -VI-co -Py on FLG film is thus demonstrated.
Moreover, the as-prepared film shows an electrical conductivity of 9.3 ×
103 S m-1. After annealing at 200oC for 10 h in N2, it further
increases to 4.0 × 104 S m-1 with no
obvious weakening in bending tolerance. The combination of good
toughness and excellent electrical conductivity in a single material
system makes FLG films developed here very promising find some important
applications, such as flexible and portable electronic
devices.59