Carbon nanotubes possess great potential for application in energy storage, composite materials, and other fields due to their excellent mechanical and electrical properties. However, the strong van der Waals forces caused by their high aspect ratio make them prone to agglomeration, significantly reducing their application effectiveness. The selection of solvent systems and the optimization of dispersion processes are key to overcoming this challenge. NMP and water, as two mainstream solvents, have distinct dispersion mechanisms and technical approaches.
NMP, as a typical polar organic solvent, exhibits good compatibility with the surface of carbon nanotubes and can achieve initial dispersion by weakening intermolecular forces. In a pure NMP system, the hydrophobic framework of carbon nanotubes forms weak interactions with the polar groups of the solvent, reducing the driving force for agglomeration. However, relying solely on the solvent is insufficient to dismantle native agglomerates; mechanical dispersion methods are necessary. High-pressure homogenization technology generates high-speed shearing, cavitation effects, and impact forces through slit valves, efficiently breaking down macroscopic secondary agglomerates. Subsequent micro-jet high-pressure homogenization creates supersonic opposing jet collisions, generating a uniform high-energy field that overcomes van der Waals forces between primary agglomerates, achieving nanoscale unbundling.
Aqueous systems are favored due to their environmental friendliness and low cost; however, the hydrophobicity of carbon nanotubes makes their dispersion significantly more difficult than NMP. A stable dispersion system requires a synergistic effect of chemical modification and mechanical dispersion. Non-covalent functionalization is the mainstream strategy; dispersants adsorb onto the carbon nanotube surface through hydrophobic interactions or π-π stacking, with the hydrophilic ends repelling water molecules and preventing re-agglomeration. Optimizing the dispersant concentration can improve stability; for example, adjusting the dispersant ratio for carbon nanotubes with different solid contents can achieve low agglomeration rates and long-term storage stability.
Serial dispersion processes are the core pathway to improving dispersion quality. First, high-speed shear emulsification ensures thorough fusion of the dispersant and solvent. Then, carbon nanotubes undergo pre-dispersion treatments such as ultrasonication and ball milling to ensure uniform wetting of the solid-liquid system. Subsequently, high-pressure homogenization breaks down macroscopic agglomerates, and finally, microfluidic treatment achieves single-tube dispersion, forming a slurry with a narrow particle size distribution and excellent stability. This process balances dispersion efficiency with the structural integrity of carbon nanotubes, avoiding defects introduced by excessive mechanical processing.
Maintaining dispersion stability requires consideration of both kinetic and thermodynamic equilibrium. The NMP system achieves kinetic stability through solvation, while the aqueous system relies on the steric hindrance and charge repulsion effects created by the dispersant. Characterization results show that optimized processes can break through traditional limitations in the solid content of carbon nanotube slurries while maintaining low viscosity and good flowability, meeting downstream processing requirements. Future research should further optimize process parameters and develop efficient and environmentally friendly dispersants to promote the large-scale application of carbon nanotubes in various fields.
