How to improve nanoparticles to make them more superior nanomaterials
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Update time : 2019-07-30 15:13:06
Agglomeration of nanoparticles
The agglomeration of nanoparticles can be divided into two types: soft agglomeration and hard agglomeration. Soft agglomeration is mainly caused by the electrostatic force between particles and van der Waals force. Due to the weak force, soft agglomeration can pass some chemical methods.
The law or the application of mechanical energy to eliminate; the formation of hard agglomeration in addition to electrostatic forces and van der Waals forces, there are chemical bonds, so hard agglomerates are not easy to destroy, need to take some special methods to control.
Schematic diagram of agglomeration of nanoparticles
Dispersion of nanoparticles
One of the methods to prevent the formation of high-density, hard-block precipitates of nanoparticles is to reduce van der Waals attraction or interaction between groups, so that the primary particles are not easily agglomerated to form secondary particles, thereby avoiding further inter-atomic bonding. This results in the formation of high-density, hard-blocked precipitates. The anti-agglomeration mechanism of nanoparticles is divided into: (1) electrostatic stabilization (DLVO theory); (2) steric stabilization; (3) electrostatic steric stabilization.
The electrostatic stabilization mechanism, also known as the electric double layer stabilization mechanism, forms an electric double layer by adjusting the pH value to produce a certain amount of surface charge on the surface of the particle. The attraction between the particles is greatly reduced by the repulsive force between the electric double layers, thereby realizing the dispersion of the nanoparticles. The mechanism is shown as shown in Figure 2.
Stochastic stabilization mechanism
The steric stabilization mechanism is to add a certain amount of uncharged polymer compound to the suspension to adsorb it around the nanoparticles to form a microcell state, which causes repulsion between the particles, thereby achieving the purpose of dispersion. The mechanism diagram is shown in Figure 4.
Electrostatic steric stabilization mechanism
The Electrostatic Stabilization mechanism is a combination of the former two, that is, adding a certain amount of polyelectrolyte to the suspension to adsorb the polyelectrolyte on the surface of the particle.
The pH value of the polyelectrolyte maximizes the dissociation degree of the polyelectrolyte, so that the polyelectrolyte on the surface of the particle reaches the saturated adsorption, and the two together work to uniformly disperse the nanoparticles. The mechanism diagram is shown in Figure 3.
Nanoparticle dispersion method
The dispersion of nanoparticles in the medium is usually divided into three stages: 1 liquid wetting the solid particles; 2 dispersing the larger aggregates into smaller particles by external force; 3 stabilizing the dispersed particles, ensuring that the powder particles are in the liquid The phase remains uniformly dispersed for a long period of time to prevent the dispersed particles from re-aggregating. According to different dispersion mechanisms, it can be divided into mechanical action method and surface modification method.
Mechanical action
The mechanical action method refers to the use of the instrument and equipment to increase the dispersion stability of the nanoparticles in the solvent, mainly mechanical stirring method, ultrasonic dispersion method and high energy treatment method. Mechanical agitation dispersion is a simple physical dispersion, mainly by mechanical energy such as external shear or impact force, so that the nanoparticles are well dispersed in the medium. Ultrasonic dispersion is a local high temperature, high pressure or strong shock wave and micro jet generated by ultrasonic cavitation, which can greatly weaken the nano-action energy between nanoparticles and effectively prevent the nanoparticles from agglomerating and fully dispersing.
Surface modification
Surface modification of nanoparticles by inorganic substances
The surface of the nanoparticle is uniformly coated with an inorganic substance, and the active hydroxyl group on the surface of the nanoparticle is coated or shielded to reduce the activity of the nanoparticle and stabilize the inner nanoparticle. The inorganic matter and the surface of the nanoparticle are not easily chemically reacted, and the inorganic substance is used for precipitation reaction on the surface of the nanoparticle, and the modifier and the nanoparticle generally rely on physical or van der Waals force.
Surface modification of nanoparticles by organic matter
The organic coating is the use of functional groups in organic molecules on the surface of inorganic nanoparticles to adsorb or chemically coat the surface of the particles, so that the surface of the particles is organized to achieve surface modification.
conclusion
The surface modification technology of nanoparticles is an edge discipline closely related to many other disciplines, including colloidal chemistry, organic chemistry, crystallography, nanomaterials, modern instrument analysis and testing. The surface coating modification technology has been widely used in the surface modification of nanometers, and the research results in this area also show that the surface coating technology has a good development prospect. However, the modification mechanism, modification method and equipment, and the modification effect characterization are still not perfect. Many times, the problem cannot be solved fundamentally, and further research is urgently needed. Due to the significant changes in the physical and chemical properties of the surface-treated particles, the development of nano surface modification technology is considered an important means of generating new materials in the future. With the continuous research and understanding of nano-particles, and further exploration of the surface modification of nano-powders, nano-technology will certainly exert potential power in different fields and will produce a good society. Benefits and economic benefits.
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