Graphene is a honeycomb planar film formed by sp2 hybridization of carbon atoms, a quasi-two-dimensional material with only one atomic layer thickness, so it is also called single-atom layer graphite.
It can adsorb and desorb various atoms and molecules, and is super hydrophobic and super lipophilic. It is just suitable for surfactants. It helps the chemistry of graphene better and contributes to the formation of graphene. It has excellent storage stability, no delamination and no back coarsening.
The most commonly used inorganic peroxides are persulfates, such as potassium persulfate Kz S zOg and ammonium persulfate (NH)aS2Og, the structural formula is as follows:
Persulfate is soluble in water, and it is decomposed according to a first-order reaction when heated, and the peroxide bond is split to generate sulfate radicals, such as:
Heating K: SOg pad 2K++2SO7·(4-19) acid has a catalytic effect on the decomposition of persulfate, and the decomposition rate increases with the decrease of pH value. When the pH value drops below 3, the decomposition rate increases faster , While deviating from the first-order reaction.
The generated sulfate radical reacts further in water:
SOT·+HZ O—HS OT+HO·(4-20)
4HO·—2HO+02(4-21) In the presence of monomers, both SO7· and modified polyethylene wax HO· radicals can initiate monomer polymerization, or they can react according to formula (4-21), releasing oxygen to make free radicals disappear . According to the formula (4-20), the HSO generated by the reaction reduces the pH value of the system. Therefore, in the absence of a buffer, the persulfate will automatically accelerate the decomposition.
The higher the temperature, the smaller the effect of pH on the decomposition rate of persulfate. The effects of temperature and pH on the decomposition rate of persulfate are shown in Table 4-6.
Generally, the pH value of the emulsion polymerization medium is greater than 4.5, and the half-life at 60℃ is 38.5h. It is longer than the polymerization time, so the general polymerization reaction is carried out at 60~80℃. When there are reducing components such as emulsifier and sulfuric acid in the system, it can accelerate the decomposition of persulfate.
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