Interfacial Matching of Nanoparticle Chain Polymer Chains

2.1 Reactive Polymer/Nano-Silica Composites For reactive polymers, polymer chains contain reactive groups that, when cured or cured, can form covalent bonds between polymer chains. In the composite of nano-silica/reactive polymers, the nano-silica particles need to be surface-treated in order to promote good dispersion of the nano-silica in the matrix. Silica coupling agents with reactive groups are commonly used for the treatment of silica: among unsaturated polyester resins, silicone coupling agents containing methacryloxy, vinyl, and epoxyalkyl groups are used; Epoxy-based, amino-hydrocarbon-containing silicon coupling agents are used; phenolic resins are selected from ammonia-containing silicon coupling agents: sulfur-vulcanized rubbers, and silicon-containing coupling agents are used. The groups in these silane coupling agents and the macromolecules in different substrates have strong reactivity and can form a covalent bond between the silica nano-metane surface and the polymer chain. There are numerous indications that a strong chemical bond is required between the two to effectively improve the overall performance of the composite.

2.2 Non-reactive polymers/nano-silicon composites For non-reactive polymers, the polymer chains do not contain reactive groups and the polymer chains cannot form covalent bonds. There are interfacial interactions between the surface of nano-Si2 particles and macromolecules including ionic bonds, coordination bonds, hydrogen bonds, electrostatic interactions, hydrophilic and hydrophobic balances, and van der Waals forces. In this way, the interface layer between the nano-SiO 2 particles and the macromolecules is formed, and the interfacial layer of the binding polymer is increased (in the rubber industry, the bound polymer is generally referred to as the binding rubber), the swelling volume fraction decreases, and the cross-linking point of the polymer after curing or vulcanization The effective molecular weight decreases. It must be pointed out that in non-polar or weakly polar polymers, a silane treatment agent is usually used to reduce the polarity of the surface of the Si2 particles so that the solubility parameter of the organic functional groups on the surface of the particles is close to that of the polymer, and the wettability of both is improved. Compatibility. If the non-reactive polymer is a crystalline germanium molecule, good wettability and miscibility between the monodisperse nano-Si2 and the macromolecule are conducive to the improvement of the nucleation of the particles, and the increase of the crystallization rate of the matrix, resulting in ultrafine crystal grains. To improve the strength of composite materials; if the non-reactive polymer is a polar polymer (such as nylon, polyamide, polycarbonate, polyester, etc.), there is an isolated, ortho-position on the surface of the nano-Si2 with amorphous structure. The active and double hydroxyls of several forms, the surface of the active hydroxyl is weakly acidic, and the polar polymer can be acid-base effect, can get quite good reinforcing effect. There are numerous indications that, although there is no covalent bond between the two, as long as there is good wettability and compatibility, it can effectively improve the overall performance of composite materials.

3. The intrinsic nano-Si2 should be well dispersed in the matrix, and the affinity between the macromolecule and the surface of the Si2 nano-particle must be better, and the interaction between the two is greater than the interaction between the nano-particles themselves. However, nanoparticle chains have a very high surface free energy and tend to agglomerate to reduce their surface free energy to a stable state. Finally, structurally loose secondary agglomerates exist in the product.

For example, Degussa AG R972 gas phase Si2 product, its primary particle size 16nm density 2560kg/m3, its secondary agglomerate size on the order of hundreds of microns, the density is only 25kg/m3, is one percent of the density of primary particles . According to the dispersion degree of Si2 nanometer powder in the medium, its size ranges from 10 to 100 micrometers. If the Si2 nanopowders are stored as loose aggregates in the final product of the polymer, the density of which is far less than the density of the primary particles, then the agglomerate becomes a defect of the product. "Same-sex aggregation,” high-polar Si2 nanoparticle chains are difficult to stretch and disperse in low-polarity polymers during the mixing process, and low-polarity polymer chains are also difficult to associate with 篼-polar Si2 nanoparticle chains. At this time, a surface treatment agent is added to modify the Si2 particles, reduce the Si-OH groups, reduce the polarity of the surface, and make the particles and the polymer molecules have similar polarities, thereby adsorbing and tightly entangling each other. If all the -OH groups on the surface of Si2 particles are removed, the alkyl group in the surface treatment agent completely shields the surface of the Si2 particles, thereby affecting the affinity of the polar or semi-polar polymer chains and the Si2 nanoparticle chains (Note: At this time, the Si2 particles are completely shielded from the thixotropic effect in the polar system by the alkyl group). Such examples show that when the surface polarity of the modified Si2 particles must be similar to the polarity of the dispersion medium, both can be affinity and adsorbed to each other. Therefore, whether or not the inorganic nanoparticles are in close affinity with the polymer is always an aspect of the success or failure of the polymer modification. On the other hand, with the advancement of composite materials to the nano level, the importance of the interface has become more prominent and has become a very active research area. After long-term research, it was found that the interfacial strength between the nano-Si2 particles and the ruthenium molecule was matched with the strength of the ruthenium molecular chain to enhance the reinforcing properties of the composite material: after curing or vulcanization, the polymer chains were The formation of covalent bonds (ie, strong interactions) requires the covalent bonding (ie, strong/strong matching) between nano-Si2 particles and macromolecules; if there is no covalent bond between macromolecule chains. Bond interactions (ie, weak interactions) also correspond to weak interactions between nano-Si2 particles and macromolecules (SP weak/weak matching). The reason for this is that the strength of the interface should be moderate enough to allow the polymer chains to slide or de-bond on the surface of the nano-Si2 particles at the right time, while maintaining partial adhesion to the substrate in a relatively large strain range. It facilitates stress transfer, passivating crack propagation, and dissipating more energy. If the interface strength is too low, the polymer chains have small sliding resistance on the surface of the Si2 particles, and the energy dissipation is also small, easily causing de-bonding, resulting in micro cracks at the interface. If the interface strength is too high, the polymer chains slide on the surface of the Si2 particles. Blocked, the main energy-dissipating polymer is a polymer, which easily induces matrix damage and is not conducive to enhancing toughening. What happened? The interfacial strength between macromolecules and macromolecules should be greater than the critical shear yield strength of the "matrix layer" and less than the fracture strength of the base rest. If the above conditions can be met, under the action of external force, no interface de-bonding occurs at first, and Si2 particles can play a role of transferring stress until interface de-bonding occurs under higher stress; due to high interfacial bond strength In the critical shear yield stress of the matrix, after the interface is debonded, with the release of the three-dimensional stress field, the "matrix layer" is in plane stress state, shear deformation occurs, the crack is passivated, and the plastic yield deformation occurs. A large amount of energy is dissipated during the fracture process.