How To Modify The Surface Of Nanoparticles
After the material is micro-nanosized, especially in the nano-state, its size is between atoms, molecules and bulk materials, so it is called the fourth state of matter. As nanoparticles have many special properties, people have shown great enthusiasm for the research of nanomaterials. They have synthesized a variety of nano- and nano-composites with advanced functions and outstanding performance, which are widely used in various fields. The fine particle size, large specific surface area, insufficient atomic coordination and high surface energy of the nanoparticles make these surface atoms highly active, extremely unstable, and easy to agglomerate. This agglomerated secondary particles are difficult to exert their nano-effects, making the material less than ideal. Therefore, in order to improve the dispersibility of nanoparticles in a polymer mixture system and increase the binding force of nanoparticles to other components, surface modification of the nanoparticles is required. Nanoparticle surface modification refers to the modification and processing of the surface of nanoparticles by physical and chemical deep processing methods, thereby controlling the internal stress, increasing the repulsive force between the nanoparticles, reducing the gravitation between the particles, and purposefully changing the surface of the nanoparticle Physical and chemical properties(morphology, crystal structure, defect state, stress state, functional group surface energy, surface hydrophobicity, surface wettability, surface potential, surface adsorption and reaction characteristics, etc.), which give the nanoparticle a new function and meet the needs of nanoparticle processing and application.
The Reason for The Agglomeration of Nanoparticles
Due to the special surface structure of the nanoparticles, there is a function between the particles that is different from the conventional particles (particles) – the nano-acting energy (Fn). Qualitatively speaking, the nano-action energy is the intrinsic property of the surface of the nanoparticle due to the lack of adjacent coordination atoms, and the intrinsic properties of the nanoparticles are agglomerated with each other. The physical meaning should be the adsorption force of nanoparticle of the unit specific surface area. It is the sum of adsorption of several aspects of nanoparticles: hydrogen bonding between nanoparticles, adsorption by electrostatic interaction; quantum tunneling between nanoparticles, charge transfer and localized adsorption of interface atoms; large specific surface of nanoparticles Adsorption. Nano-effect energy is an intrinsic factor for the easy aggregation of nanoparticles. To obtain nanoparticles with good dispersibility, small particle size, and narrow particle size distribution, the nano-action energy must be weakened or reduced.
Nanoparticle Surface Modification Method
Existing methods for surface modification of nanoparticles can be classified into physical modification and chemical modification depending on the treatment method selected.
Surface Physical Modification
Surface physical modification generally refers to a method of surface modification of micro/nano powders without surface modifiers, including radiation treatment of electromagnetic waves, neutron fluxes, alpha particles, beta particles, and sonication, plasma treatment, heat treatment, Electrochemical treatment, etc.
- Radiation Treatment
Radiation technology is a new technology for the research, development and application of the laws of physics, chemistry and biological effects caused by the interaction of ionizing radiation and matter. Active spots are generated on the surface of the nanoparticle by high-energy irradiation, and the active organic monomer is grafted on the surface of the polymer film to change the surface properties of the micro-nano particles and increase the compatibility with the polymer material.
- Ultrasonic Treatment
Ultrasonic dispersion is an effective method to reduce the agglomeration of nanoparticles. By using local high temperature, high pressure or strong shock wave and micro jet generated during ultrasonic cavitation, the nano-effect energy between nanoparticles can be weakened to a large extent, and nano-particle agglomeration can be effectively prevented. And make it fully dispersed.
- Plasma Treatment
Plasma treatment has the following advantages: (1) Only the properties of a thin layer on the surface of the nanoparticle change, and other characteristics, such as particle size and distribution, do not change significantly; (2) the process requires very little energy, and the whole process does not A solvent is required; (3) The properties of the polymer, such as functional groups, reactivity, and the like, may vary depending on the application. However, the disadvantage of this treatment method is that it needs to be carried out under vacuum.
Surface chemical modification
Surface chemical modification refers to a method of changing the structure and state of the surface of a nanoparticle by chemical reaction or chemisorption between the surface of the nanoparticle and the treatment agent to achieve the purpose of surface modification. The surface chemical modification method plays an extremely important role in the surface modification of nanoparticles. It is the most commonly used surface modification method, mainly esterification reaction method, surfactant method, coupling agent method and surface graft reaction method and so on.
- Esterification Reaction Method
The reaction of metal oxides with alcohols is called esterification. The most important aspect of surface modification of nanoparticles by esterification is to change the surface of the original hydrophilic and oleophobic to a lipophilic and hydrophobic surface. It is very important in practical applications.
- Surfactant Modification Method
Surfactant molecules consist of two distinctly identifiable components, one being an oleophilic group that has an affinity for oil or organic matter, and the other being a hydrophilic group that has an affinity for water or an inorganic substance. The structural characteristics of the surfactant enable it to be applied to the surface modification treatment of nanoparticles, so that the hydrophilic groups on the surface of the nanoparticles become oleophilic groups, thereby improving the affinity of the nanoparticles with organic substances, improving compatibility and dispersibility.
- Coupling Agent Method
The coupling agent is a chemical substance having an amphoteric structure and is mainly used as an auxiliary agent for polymer materials. A part of the group in the molecule can react with various functional groups on the surface of the powder to form a strong chemical bond, and another part of the group can undergo some chemical reaction or physical entanglement with the organic polymer. Therefore, the coupling agent is called a “molecular bridge” to improve the interfacial interaction between the inorganic substance and the organic substance, thereby greatly improving the performance of the composite material. Commonly used coupling agents are mainly silane coupling agents, titanate coupling agents, zirconium aluminate coupling agents, aluminate coupling agents, and the like.
- Surface Graft Modification
Surface graft polymerization is a process in which a polymer material is bonded to the surface of an inorganic particle by a chemical reaction. Some of the hydroxy or unsaturated bonds present on the surface of some inorganic particles (such as SiO2, TiO2, Al2O3, carbon black) can be directly used to graft the polymer, or the hydroxyl group is further reacted, and grafting is carried out after introducing various functional groups. Grafting polymer molecules on the surface of nanoparticles has a greater advantage than using surfactants or coupling agents, which not only improves the dispersion stability of nanoparticles, but also enhances the compatibility of nanoparticles with resin matrix. The polymer grafted particles will have adjustable properties by selecting suitable grafting monomers and grafting conditions.
Due to the agglomeration of nanoparticles, the surface modification of nanoparticles is directly related to the application of nanoparticles. At present, there are many methods for surface modification, but there are still few ways to solve the problem fundamentally, and further research is needed. In addition, in the surface modification of nanoparticles, the composite use of modifiers should also be considered in order to achieve better modification effects.