Carbon nanotubes, as nanomaterials with a unique one-dimensional tubular structure, possess excellent mechanical strength, electrical conductivity, and thermal conductivity, demonstrating immense application value in fields such as electronic devices, composite materials, and energy storage. However, carbon nanotubes exhibit strong van der Waals forces, making them prone to aggregation and the formation of large aggregates. This not only masks their superior nanoscale properties but also hinders their uniform distribution in the matrix material, severely limiting the expansion of their applications. Therefore, carbon nanotube dispersion technology has become the core to overcome this bottleneck and is a crucial link in fully leveraging their material advantages and promoting industrial applications.
The core principle of carbon nanotube dispersion is to weaken or even break the van der Waals forces between carbon nanotubes through physical or chemical means, dismantling the aggregated carbon nanotubes into single or a small number of dispersed units, and ensuring their stable existence in the dispersion medium. From a molecular perspective, the dispersion process needs to achieve two goals: first, to disrupt the structure of aggregates and expose the surface of carbon nanotubes; and second, to construct a "protective mechanism" on the surface of carbon nanotubes—by adsorbing dispersant molecules or introducing functional groups to form a repulsive layer on the surface, preventing the dispersed carbon nanotubes from re-aggregating and ensuring the long-term stability of the dispersion system.
Achieving efficient dispersion of carbon nanotubes requires precise control of three key influencing factors. First, the choice of dispersion medium is crucial. An ideal dispersion medium must have good compatibility with the carbon nanotube surface. Commonly used media include water, ethanol, and N-methylpyrrolidone. Highly polar media usually require the use of surfactants, where the hydrophilic groups of the surfactant bind to the medium, and the hydrophobic groups adsorb onto the carbon nanotube surface, achieving dispersion. Non-polar media, on the other hand, can reduce the probability of collisional aggregation of carbon nanotubes by adjusting the solvent viscosity. Second, the type and amount of dispersant must be appropriately matched. Dispersants are mainly classified into three categories: surfactants, polymers, and small-molecule modifiers. Different dispersants have different mechanisms of action: surfactants achieve dispersion through charge adsorption, polymers stabilize the system through steric hindrance, and small-molecule modifiers alter the surface properties of carbon nanotubes through chemical grafting. Insufficient dosage leads to incomplete dispersion, while excessive dosage introduces impurities, affecting the subsequent performance of the material. Thirdly, dispersion process parameters need optimization. Whether using ultrasonic dispersion, mechanical stirring dispersion, or ball milling dispersion, key parameters must be adjusted. Taking commonly used ultrasonic dispersion as an example, the ultrasonic power and processing time need to be adjusted according to the diameter and length of the carbon nanotubes. Too low a power will fail to break down the aggregates, while too high a power may cause the carbon nanotube structure to break, resulting in a loss of its inherent properties.
In practical applications, breakthroughs in carbon nanotube dispersion technology have brought innovation to many fields. In the field of electronic devices, uniformly dispersed carbon nanotubes can serve as a core component of conductive pastes for the fabrication of flexible circuit boards. Their conductivity is more than 30% higher than traditional metal pastes, while also being lighter and more flexible. In the field of composite materials, dispersed carbon nanotubes combined with resin matrices can produce high-strength, high-thermal-conductivity aerospace materials, significantly improving their impact resistance and thermal management capabilities. In the field of energy storage, uniformly dispersed carbon nanotubes, as conductive additives in lithium-ion battery electrode materials, can effectively improve the conductive network within the electrode, enhancing the battery's charge-discharge efficiency and cycle life.
With the deepening of nanomaterial research, the requirements for the uniformity, stability, and large-scale production of carbon nanotube dispersion are increasingly stringent. In the future, by developing novel environmentally friendly dispersants and optimizing multi-process synergistic dispersion technologies, carbon nanotube dispersion technology will further overcome existing limitations, providing high-performance material support for more high-end fields and propelling the nanomaterials industry towards a higher-quality development stage.
