2.3. Preparation of PVA/rGO nanocomposites
PVA/GO nanocomposites containing different amount of filler
were prepared as follows: GO was dissolved in 20 mL of water
and treated with ultrasound for 15 min at room temperature to
yield a clear solution. PVA (1 g) was dissolved in distilled water
(10 mL) at 98 C for 1 h. The GO aqueous dispersion was gradually
dropped into the PVA solution, and stirred at 98 C for 30 min. No
precipitate was observed in a few hours after magnetic stirring, it
indicates that no GO aggregate was formed. The homogeneous
PVA/GO solution was poured into an aluminum dish and kept at
60 C for 15 h to cast film. This film was peeled off from the substrate
before reduction.
The reduction of GO to graphene has been achieved in the mixture
of NaOH and Na2S2O4. The obtained black material was identified
to be rGO using Solid State 13C NMR spectroscopy, X-ray
photoelectron spectroscopy and electrical conductivity measurements.
Such a reduction process has been described in detail elsewhere
[17]. Here, the same method is used to reduce PVA/GO films.
The reducing agent solution was prepared by dissolving 2 g of
NaOH and 0.5 g of Na2S2O4 in 50 ml of distilled water, where the
NaOH acts as a catalyst and stabilizer. The PVA/GO film was dipped
into reducing agent solution at 60 C for 1 h to yield completely
reduced PVA/rGO composites. After reduction, the color of the film
changed from yellow-brown to black. The prepared PVA/rGO films
were rinsed with distilled water until complete removal of residual
material (including reducing agents and byproduct Na2SO3). Then
PVA/rGO films were cut into specimens in the size of
60 10 mm using a razor blade and kept at 50 C for 5 h under
vacuum to further remove remaining moisture prior to mechanical
test. Furthermore, neat PVA underwent the same process described
above is used as reference material. In the following text, the
marked contents of rGO is actually the contents of GO. Obviously,
the true content of rGO is less than that of GO as the oxygenfunctional
groups have been removed during reducing process.
However, the effect of rGO can still be demonstrated in the trend
discussed below.