Functional modification of graphene-hydrophobic and hydrophobic

Graphene has a high chemical stability on the hexagonal benzene ring graphene surface, and the interaction force with other media is very weak, and the van der Waals force between the sheets is too strong, resulting in no hydrophilicity and no hydrophilicity. It is almost impossible to be compatible with other media or polymers. Easy to get together. However, graphene can not exist alone in nature and must be prepared by modern processes. It is more common to reduce graphene to oxide ink.

Graphene oxide has long been regarded as a hydrophilic substance because of its excellent dispersion in water. However, related experimental results show that graphene oxide is actually amphiphilic, showing hydrophilic to hydrophobic properties from the edge of the graphene sheet to the center. distribution. Therefore, graphene oxide can exist as an interfacial active agent and reduce the energy between the interfaces. Its hydrophilicity is widely recognized.

The force between the oxide ink layer and the layer decreases due to the increase in the layer spacing, and the hydrogen bond force of the hydrophilic functional group and the water molecule generated by the oxide graphene surface is repulsion of the charge formed by the deprotonation of the carbonyl group. The graphite oxide can be evenly dispersed in water. Form a single layer of graphene oxide suspension. In order to obtain graphene, graphene oxide, which is evenly dispersed in aqueous solution, needs to be reduced to yttrium-reduced graphene rGO, the SP 3 bond is deoxygenated to SP2 bond, and most of the reduction of graphite oxide is done by strong reducing agents such as Hydrazine(N2H4). Reduction, However, after reduction, accumulation and precipitation are usually formed and can not be present in a stable suspension. This reason is mainly due to the conversion of highly hydrophilic graphene to highly hydrophobic graphene in order to reduce surface energy., Hydrophobic graphene tends to form aggregates. However, if the interface active agent is used properly to modify the reduced graphene surface and increase hydrophilicity, the stability of the reduced graphene suspension can be improved.

In this way, we can roughly come up with the following first conclusion.

What is the oil-friendly end and the water-friendly end? The more commonly used example is soap. The soap molecule has a long chain of many carbon and hydrogen at one end, which is called an oily end; The other end is a hydrophilic atomic group called a hydrophilic end. When using soap, the oil is adsorbed by the pro-oil end, and then pulled into the water by the hydrophilic end to achieve the washing effect.

As for the interface active agents commonly used in polymers, the molecules are composed of Non-Polar hydrophobic(oil-friendly) atomic groups and polar hydrophilic groups, and the two parts can be relatively concentrated to form a part of hydrophilic and a part of the pro-oil. Two parent molecules.

Its hydrophilicity comes from the electrical interaction between polar groups and water molecules or the formation of hydrogen bonds, which makes the interfacial active agent molecules have dissolving properties. Non-polar groups can not only have such affinity with water, but also cause the surrounding water molecules to form ice-like structures and lose freedom of movement. If the Non-Polar group leaves the water environment, the ice-like structure of this part of the water will disintegrate, resulting in an increase in system entropy and a decrease in the Gibbs function to facilitate the process. This is the hydrophobic effect.

It gives the surfactant molecules a tendency to escape from the water phase. The structural affinity makes the surfactant have two important basic functions: the adsorption of the surface of the solution and the formation of colloidal groups inside the solution.

In recent years, Super hydrophobic and hydrophobic materials have been favored in oil and water separation due to their special wettability. Since the surface tension of the oil is much smaller than that of water, the superhydrophobic surface is difficult to prepare, and the superhydrophobic surface is mostly superhydrophobic, which limits its application in oil and water separation. So, let's try to fill in the gaps in the fourth quadrant above, which is that we're going to find the members of the graphene family who are hydrophilic, and we're going to try to do this with graphene oxide.

According to the patented CN103623709B oxide superhydrophilic superhydrophilic superhydrophobic oil water separation membrane and its preparation and application, the hydrophilic polymer hydrosensitizer is proportional to the cross-linked membrane forming agent and then dissolved in water with the nanosilicate Sol according to the ratio of quality. Magnetic stirring is evenly prepared into a solution with a concentration of 1 to 99 %, and 0.5 to 1 % of graphene oxide is added as an inorganic crosslinking agent, and the ultrasonic dispersion is uniform; 100 to 300 mesh fabric mesh ultrasonic cleaning, room temperature drying, spraying, immersion or spinning coating on the silk network film, drying cross-linking, to obtain Super hydrophilic and underwater Super oil separation omentum. The key is that the oil and water separation omentum has a special nanometer and micron composite structure, Micron scale mesh holes, Micron thickness organic-inorganic doping cladding layer and nanometer size protruding structure on the cladding layer. The oil and water separation omentum has a contact angle of 0 ° between air and water and oil, but it has an ultra-hydrophobic property underwater. So let's go further and come up with the second conclusion.

Plasma surface modification is based on the principle of free radicals or specialized functional groups formed on the surface after plasma activation, and there is selective reinforcement of surface characteristics. Plasma treatment also provides a simple surface modification of the material, and different atoms and groups can be introduced on the surface of the molecular material. The use of oxygen plasma treatment to irradiate graphene can completely convert graphene to graphene oxide. Secondly, plasma modification can also be used to increase the hydrophobicity of graphene. Example: Oxygen plasma treatment can increase the surface hydrophilicity of the material, while HMD, CF4 plasma treatment energy lift hydrophobic properties.

As a thin surfactant, GO's amphoteric comes from its hydrophilic edges and hydrophobic groups on the surface. Like Ionic surfactant molecules, its duality may be due to the edge? The degree of ionization of the COOH group, or the pH of the dispersed liquid, varies(Figure a). A higher pH may cause the charge on the edge to increase, thus increasing the hydrophilicity of the sheet. Similarly, the edge of GO? Right? The arrangement of hydrophilic and hydrophobic groups in the center suggests that the size is also a parameter that affects the characteristics of its parents.

The smaller sheet has a higher edge? Right? The proportion of the area and therefore has more hydrophilicity(Figure B). Finally, the size of the hydrophobic nanometer graphene region on the base surface of the GO sheet can also be adjusted by varying degrees of reduction, or by removing its oxygen functional group from the graphene sheet(Figure C). As shown in figure D, the pH value, size, and degree of reduction will affect the charge density and the hydrophilicity of GO: the charge density of the GO sheet decreases with the pH value, the size of the graphene sheet, and the degree of reduction. Increase and decrease. Since GO's hydrophilic properties are related to size, the new concept of GO size separation is inspired. Since the large-sized GO sheet is more stable to the water surface, and is a better emulsifying active agent, Therefore, the size of the GO sheet can be separated by water surface filtration or emulsifying extraction.

Let's talk about fluorinated graphene. As a new derivative of graphene, graphene fluoride not only maintains the high-strength properties of graphene, but also introduces novel interface and physical and chemical properties such as surface energy reduction, hydrophobic enhancement, and bandgap expansion due to the introduction of fluorine atoms. At the same time, graphene fluoride is resistant to high temperatures and chemically stable, showing properties similar to those of polytetrafluoroethylene, which is called "divityflon." The unique properties of graphene fluoride can make it have a wide range of applications in the interface, new nano electronic devices, lubrication materials and other fields. Graphene fluoride usually uses graphene oxide and hydrogen fluoride as raw materials, and then the preparation of graphene fluoride with high quality and adjustable fluorination is also achieved through water-thermal reactions. Therefore, we can sort out the final conclusions.

Fun, so it is said that graphene is not a material, according to the need to adjust the use of the king, graphene under different processes and different functions of new materials is the most basic tool for the growth of the graphene industry. Looks like I'm going to do hydrophobic hydrophobic paint should have a spectrum.

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