Agglomeration of nanometer powders Solution for
(Liu Tao Shanghai Huijingya Nano New Material Co., Ltd.)
Nanomaterials have unique mechanical, optical, thermal, electrical, magnetic, adsorption, gas sensing and other properties. Adding nano powders to traditional materials will greatly improve their performance or bring unexpected properties. However, in the process of practical application, due to the small size and high surface activity of nanoparticles, they are easy to agglomerate and form larger agglomerates, which seriously hinders the application of nano powders and the preparation of corresponding nano materials 。
Agglomeration of nano powder
At present, many nano products on the market are characterized and found to contain both nano and micro particles, which cannot achieve the real nano standard（ 1-100nm ）The main reason is that the powder agglomeration is serious, and the nanometer particles are agglomerated into large particles.
one Why do nanometer powders agglomerate?
The so-called agglomeration of nano powder refers to the phenomenon that the original nano powder particles are interconnected and form large particle clusters from multiple particles in the process of preparation, separation, treatment and storage, which is generally divided into soft agglomeration and hard agglomeration.
The agglomeration and dispersion of nano powders depend on their morphology and surface structure. The morphology and surface structure of nano powder are related to its internal structure, impurities, surface adsorption and chemical reaction, preparation process, environmental status and other factors, which lead to the agglomeration of nano powder and Dispersion machine The complexity and diversity of the system.
2、 How to solve the problem of agglomeration of nano powder?
In order to solve the problem of agglomeration of nano powder, it is necessary to use certain means to uniformly disperse the nano powder. The dispersion methods of nano powder mainly include ultrasonic dispersion, mechanical dispersion and chemical dispersion. At present, the most widely used is chemical dispersion, that is, surface modification.
3、
Surface modification It refers to the chemical reaction and physical action on the surface of particles through the use of surface additives, so as to change the surface state of particles, such as the surface atomic layer structure and functional groups, surface hydrophobicity, electricity, chemical adsorption and reaction characteristics. Through surface modification, the dispersity, durability, weather resistance and surface activity of the powder can be improved, so that the particle surface has new physical, chemical and optical properties, which can meet different application requirements, expand its application fields and significantly increase the added value of materials.
There are many methods for surface modification of nano powder, including coating treatment, precipitation reaction, surface chemical modification, mechanochemical modification, high-energy treatment, encapsulation, microemulsion, etc.
（ one ）Coating treatment modification
Wrapping treatment modification, also known as coating and coating, is a method of coating the surface of inorganic or organic substances, main surfactants, water-soluble or oil soluble polymer compounds, fatty acid soaps and other powders to achieve modification. Such as coating by adsorption, adhesion and simple chemical reaction or precipitation.
（ two ）Precipitation reaction modification
The chemical reaction is used to precipitate the product on the surface of the modified powder to form one or more layers “ Modified layer ” The main method of wet modification is to change the surface characteristics of nano powder materials to meet the required use requirements.
（ three ）Surface chemical modification
This is the most important and commonly used method for surface modification. Surface chemical modification is a chemical reaction between the surface modifier and the particle surface, so that the surface modifier can cover the particle surface, change the surface structure and state of nano powder particles, and achieve the purpose of surface modification. In addition to using surface functional groups, surface chemical modification also uses free radical reaction, chelation reaction, sol adsorption and coupling agent.
The specific surface area of nanoparticles is large, and the surface bond state and electronic state are different from those inside the particles. Incomplete coordination results in a large number of dangling bonds, which provides favorable conditions for chemical reaction to modify the surface of nanoparticles.
The surface chemical modification of nano powder materials is affected by many factors. It mainly includes: the influence of surface properties of nano powder particles; Influence of the type, amount and use method of surface modifier; Influence of process equipment and operating conditions, etc.
（ four ）Mechanochemical modification
Mechanochemical modification is to activate the powder surface purposefully through the process of ultra-fine grinding and other strong mechanical force, to change the crystal structure (surface amorphous), solubility, chemical adsorption and reaction activity (increase the active point or active subordinate point of the surface) of the particle surface to a certain extent.
（ five ）High energy treatment modification
Through the action of high-energy particles such as corona, ultraviolet light, plasma radiation, microwave and so on, active spots are generated on the surface of nanoparticles to increase the surface activity, which is easy to react or absorb with other substances, so as to modify the surface of nanoparticles to achieve the purpose of easy dispersion.
（ six ）Capsulation modification
Encapsulation modification is a surface modification method that covers the surface of powder particles with a uniform film with a certain thickness.
（ seven ） Microemulsion modification
In the preparation of nanoparticles, thermodynamic stable, isotropic, transparent or translucent dispersion system of two or more immiscible liquids is formed, and microscopic micro particles are composed of droplets of one or two liquids stabilized by surfactant interface film emulsion 。 The surface of particles is coated with a layer of surfactant molecules, so that particles are not easy to coalesce. By selecting different surfactants and cosurfactants, particles can be modified and the size of particles can be controlled.
From the current development of nano materials, the agglomeration of nano powders has seriously limited the application of nano materials, The dispersion and surface modification technology of nano powder is in the development process of nano materials “ Top priority ” Technology of 。 Only by dealing with these problems, nano powder materials can play a huge role. The uniform dispersion of nano powder particles is the key to improve the performance of various materials after modification. The use of various nano powder surface modification technologies can make the surface of nano powder compatible with the matrix.
