5.6 Microemulsion Method
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5.6 Microemulsion Method
Microemulsion Method is a method of forming microemulsion with mixed metal
salts and certain precipitant, and controlling the nucleation and growth of colloidal
particles in a smaller microarea (called microreactor), and then obtaining ultrafine
particles by heat treatment. Microemulsion is usually a transparent and isotropic
thermodynamic stability system composed of surfactants, cosurfactant (usually alcohols), and oil (usually hydrocarbons). Microemulsion is surrounded by tiny monolayer of surfactant and cosurfactant. The size of it is between several to several dozens
of nanometers. These tiny pools separate each other and form microreactor.
The microemulsion particles are constantly moving like Brown motion. When
different particles collide with each other, the surface active agent and the hydrocarbon chain of cosurfactant can permeate each other. At the same time, the material in the “pool” can go through the interface into another particle. For example,
the conductance and percolation phenomenon of microemulsion formed by anionic
surfactants is due to the continuous conduction chain formed by the cations in the
pool passing through the microemulsion interface and the transition between particles. The properties of this material exchange in microemulsion make it possible to
make chemical reactions in the “pool”. Obviously, it is another effective technique
for the preparation of nanomaterials.
Usually, two kinds of reactants are dissolved in two microemulsions, respectively, which are made up of exactly the same, and then mixed under certain conditions. The two kinds of reactants encounter and react with each other through the
exchange of materials, and the growth of the reaction products will be limited when
the interfacial strength of the microemulsion is larger. If the size of microemulsion
particles is controlled in a few nanometers, the reaction products are dispersed in
different microemulsion “pools” in the form of nanoparticles. The study shows that
the nanoparticles can be stable in the “pool”. The nanoparticles are separated from
the microemulsion by adding the mixture of water and acetone to the microemulsion
through the overspeed centrifugation or the addition of the mixture of water and
acetone to the completion of the reaction. Then the organic solvent is used to remove
the oil and surfactants attached to the surface of nanoparticles. Finally, after drying
at a certain temperature, the required nanomaterials can be obtained.
One of the main obstacles to develop graphene-based supercapacitors with high
energy density is to maintain large ion-accessible surface area and high electrode
density (Xu et al. 2015). The system of ionic liquid (IL)-surfactant microemulsion
was developed by She et al., which was found to promote IL-filled micelles adsorpt
spontaneously onto graphene oxide (GO) (She et al. 2017). This adsorption not only
played an important role in distributing the IL over all available surface area, but also
act a pivotal part in providing an aqueous formulation which can be slurry cast onto
current collectors. As a result, a dense nanocomposite film of GO/IL/surfactant was
left. The IL could act as a dual role of electrolyte and spacer, via reducing the GO
and removing the surfactant (result from a low-temperature (360 °C) heat treatment).
97
5.6 Microemulsion Method
Microemulsion Method is a method of forming microemulsion with mixed metal
salts and certain precipitant, and controlling the nucleation and growth of colloidal
particles in a smaller microarea (called microreactor), and then obtaining ultrafine
particles by heat treatment. Microemulsion is usually a transparent and isotropic
thermodynamic stability system composed of surfactants, cosurfactant (usually alcohols), and oil (usually hydrocarbons). Microemulsion is surrounded by tiny monolayer of surfactant and cosurfactant. The size of it is between several to several dozens
of nanometers. These tiny pools separate each other and form microreactor.
The microemulsion particles are constantly moving like Brown motion. When
different particles collide with each other, the surface active agent and the hydrocarbon chain of cosurfactant can permeate each other. At the same time, the material in the “pool” can go through the interface into another particle. For example,
the conductance and percolation phenomenon of microemulsion formed by anionic
surfactants is due to the continuous conduction chain formed by the cations in the
pool passing through the microemulsion interface and the transition between particles. The properties of this material exchange in microemulsion make it possible to
make chemical reactions in the “pool”. Obviously, it is another effective technique
for the preparation of nanomaterials.
Usually, two kinds of reactants are dissolved in two microemulsions, respectively, which are made up of exactly the same, and then mixed under certain conditions. The two kinds of reactants encounter and react with each other through the
exchange of materials, and the growth of the reaction products will be limited when
the interfacial strength of the microemulsion is larger. If the size of microemulsion
particles is controlled in a few nanometers, the reaction products are dispersed in
different microemulsion “pools” in the form of nanoparticles. The study shows that
the nanoparticles can be stable in the “pool”. The nanoparticles are separated from
the microemulsion by adding the mixture of water and acetone to the microemulsion
through the overspeed centrifugation or the addition of the mixture of water and
acetone to the completion of the reaction. Then the organic solvent is used to remove
the oil and surfactants attached to the surface of nanoparticles. Finally, after drying
at a certain temperature, the required nanomaterials can be obtained.
One of the main obstacles to develop graphene-based supercapacitors with high
energy density is to maintain large ion-accessible surface area and high electrode
density (Xu et al. 2015). The system of ionic liquid (IL)-surfactant microemulsion
was developed by She et al., which was found to promote IL-filled micelles adsorpt
spontaneously onto graphene oxide (GO) (She et al. 2017). This adsorption not only
played an important role in distributing the IL over all available surface area, but also
act a pivotal part in providing an aqueous formulation which can be slurry cast onto
current collectors. As a result, a dense nanocomposite film of GO/IL/surfactant was
left. The IL could act as a dual role of electrolyte and spacer, via reducing the GO
and removing the surfactant (result from a low-temperature (360 °C) heat treatment).