Discussion on Dispersion of Nanodiamond Many dangling atomic bonds on the surface of nanodiamond particles greatly improve their chemical activity. The very large surface area makes them have huge surface energy, and it is inevitable to easily form hard aggregates that are difficult to depolymerize. Therefore, nanodiamonds have poor dispersion stability in the medium and are prone to aggregation, severely restricting their application. That is to say, the key technology for preparing nanodiamond polishing fluid is the long-term stable dispersion of nanodiamonds in the medium and the uniformity of particle size, which is a worldwide technical problem. The average particle size of nanodiamond dry powder is two μm. The surface of nanodiamond contains a large number of organic functional groups, mainly one OH (hydroxyl group), one C=O (carbonyl group), one COOH (carboxyl group), and some nitrogen-containing groups. It can reach 10%~25% of the particle surface. These oxygen-containing active groups and nitrogen-containing active substances can react or adsorb with many organic compounds. It provides a basis for the dispersion of nanodiamonds in oil or water media. The dispersion technology of nanodiamonds is generally divided into physical dispersion and chemical dispersion. Physical dispersion can be divided into ultrasonic, mechanical stirring, and mechanical grinding. Chemical dispersion can be divided into chemical modification dispersion and dispersant dispersion. The dispersion process of nanodiamond polishing liquid makes the nanodiamond aggregates in the liquid phase dispersed in the state of the original monomer in the polishing liquid.
The decentralization process mainly consists of two steps: First, the wetting of the particles in the liquid phase, The second is to stabilize the dispersion of primary particles without agglomeration or break the formed agglomerates into smaller or original monomer particles. Some industry experts in my country have explored nanodiamonds' stable dispersion process and mechanism in water media. They believe that mechanochemical treatment is used to modify the surface of diamonds, and mechanical forces such as high-shear stirring and high-energy ultrasonic vibration mills are used to interact with polymers. The synergistic effect of surfactants, while effectively crushing nanodiamonds, modifies the surface of nanodiamonds, especially the new surface during the crushing process, adjusts the hydrophilic and hydrophobic properties of the particle surface, and realizes the stable dispersion of nanodiamonds in the medium. Based on the results of this research, using silane coupling agent KH-570 and polymer JQ-3 surface-modified nanodiamonds, using ultrasound as a means of dispersion, dispersed them in ethanol, and obtained nanodiamonds with an average particle size of 51.7nm. The colloidal solution and two polymer dispersants are combined, which can improve the dispersibility and stability of nanodiamonds in ethanol, and lay a foundation for preparing domestic oily polishing fluid.
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