118
S. Pakdel et al.
liquid–liquid interface [92, 93]. Pickering emulsions generally have less toxicity,
less susceptibility to foaming, and lower cost in comparison with common emulsions stabilized by surfactants [94]. The properties of Pickering emulsions are determined by the size of the solid particles and their amphiphilicity. The amphiphilicity
of GO makes it perform like a colloidal surfactant. Xie et al. [95] produced PS/GO
composite particles by Pickering emulsion stabilized by GO. The results demonstrated that the pH and the size of the GO particles affect the stability of Pickering
emulsions and the final morphology of the particles, respectively. Small GO particles
were appropriate for Pickering emulsion polymerization to synthesize the composite
particles. The prepared composite particles could have a wide range of potential
applications such as in environmental remediation, catalysts, sensors, and energy
storage. Gudarzi et al. [93] reported a novel method based on Pickering emulsion
polymerization that promises well dispersion and increases loading. The main idea
of this method is to use a high affinity of GO for assembly at the liquid–liquid interface. A guideline for confirming stable hybrid colloids of polymer–GO with a proper
polymer particle size has been presented. Then, a system of polymethyl methacrylate (PMMA)–GO has been selected, and the nanocomposites have been produced
by Pickering emulsion polymerization to examine the theory. The PMMA monomer
was employed to test the feasibility of the process and up to 5 wt% of GO has been
loaded successfully. This high loading of GO paves the way for the industrial-scale
production of graphene-based masterbatches that can be used in downstream industries via melt mixing. Solvent- and soap-free characteristics increase the quality of
the nanocomposite and make the method environmentally friendly.
2.5 Spin Coating
The homogeneous thin composite films can be synthesized by spin-coating technique
in the range of micrometer to nanometer thickness. This method includes numerous
stages such as fluid dispense, spin up, stable fluid outflow, spin-off, and evaporation.
First, the material is deposited on the turntable and then spin up and spin-off are
carried out in sequence while the evaporation is occurred during the process. The
solution is dispersed on the turntable via centrifugal force, at a high velocity in a range
of 1000–8000 rpm [96, 97], which results in leaving a uniform and thin layer. After
this stage, drying of the applied layer occurs in which high volatile components
are removed from the substrate because of the evaporation or simply drying. The
thickness of the synthesized composite film is controlled by the speed of rotation
and the viscosity of the coating solution [98]. Lue et al. [99] fabricated Nafion/GO
composite membranes for direct liquid fuel cell applications with the purpose of
reducing fuel permeability and extra-improving cell performance. Nafion 212 (N212)
composites consist of various GO contents that were fabricated using spin coating
methods. The GO filling in the prepared composites had a positive relationship with
the water uptake, ionic conductivity, and ion exchange capacity. The spin-coated
composite membranes had a higher width to thickness ratio, which is the effective
S. Pakdel et al.
liquid–liquid interface [92, 93]. Pickering emulsions generally have less toxicity,
less susceptibility to foaming, and lower cost in comparison with common emulsions stabilized by surfactants [94]. The properties of Pickering emulsions are determined by the size of the solid particles and their amphiphilicity. The amphiphilicity
of GO makes it perform like a colloidal surfactant. Xie et al. [95] produced PS/GO
composite particles by Pickering emulsion stabilized by GO. The results demonstrated that the pH and the size of the GO particles affect the stability of Pickering
emulsions and the final morphology of the particles, respectively. Small GO particles
were appropriate for Pickering emulsion polymerization to synthesize the composite
particles. The prepared composite particles could have a wide range of potential
applications such as in environmental remediation, catalysts, sensors, and energy
storage. Gudarzi et al. [93] reported a novel method based on Pickering emulsion
polymerization that promises well dispersion and increases loading. The main idea
of this method is to use a high affinity of GO for assembly at the liquid–liquid interface. A guideline for confirming stable hybrid colloids of polymer–GO with a proper
polymer particle size has been presented. Then, a system of polymethyl methacrylate (PMMA)–GO has been selected, and the nanocomposites have been produced
by Pickering emulsion polymerization to examine the theory. The PMMA monomer
was employed to test the feasibility of the process and up to 5 wt% of GO has been
loaded successfully. This high loading of GO paves the way for the industrial-scale
production of graphene-based masterbatches that can be used in downstream industries via melt mixing. Solvent- and soap-free characteristics increase the quality of
the nanocomposite and make the method environmentally friendly.
2.5 Spin Coating
The homogeneous thin composite films can be synthesized by spin-coating technique
in the range of micrometer to nanometer thickness. This method includes numerous
stages such as fluid dispense, spin up, stable fluid outflow, spin-off, and evaporation.
First, the material is deposited on the turntable and then spin up and spin-off are
carried out in sequence while the evaporation is occurred during the process. The
solution is dispersed on the turntable via centrifugal force, at a high velocity in a range
of 1000–8000 rpm [96, 97], which results in leaving a uniform and thin layer. After
this stage, drying of the applied layer occurs in which high volatile components
are removed from the substrate because of the evaporation or simply drying. The
thickness of the synthesized composite film is controlled by the speed of rotation
and the viscosity of the coating solution [98]. Lue et al. [99] fabricated Nafion/GO
composite membranes for direct liquid fuel cell applications with the purpose of
reducing fuel permeability and extra-improving cell performance. Nafion 212 (N212)
composites consist of various GO contents that were fabricated using spin coating
methods. The GO filling in the prepared composites had a positive relationship with
the water uptake, ionic conductivity, and ion exchange capacity. The spin-coated
composite membranes had a higher width to thickness ratio, which is the effective