Inorganic nanofillers, with their superior physicochemical properties due to size effects, are widely used in composite materials, coatings, and nanofluids. However, due to their large specific surface area and high surface energy, nanoparticles easily aggregate through van der Waals forces and electrostatic adsorption, severely weakening their functional value. Therefore, efficient dispersion technology has become a key bottleneck in the application of nanomaterials. Ultrasonic dispersers, with their unique mechanism of action, provide a reliable solution to this problem.
The core function of ultrasonic dispersers stems from the synergistic effect of cavitation and mechanical shearing. The high-frequency vibrations emitted (20kHz-1MHz) excite a large number of tiny cavitation bubbles in the liquid medium. These bubbles, after a brief existence, rapidly collapse, releasing strong shock waves and microjets that directly break the agglomeration forces between nanoparticles, achieving initial dispersion. Simultaneously, the high-frequency vibrations themselves generate continuous mechanical shearing forces, further stripping away incompletely dispersed small aggregates and ensuring the particles exist in a more monodisperse state.
Numerous experiments have validated its effectiveness: when processing common inorganic fillers such as nano-silica and carbon nanotubes, ultrasonic dispersion significantly improves the uniformity of filler distribution in the polymer matrix, resulting in a 15%-30% improvement in key properties of the composite material, such as mechanical strength and thermal conductivity. This technology is particularly suitable for liquid media systems such as water and organic solvents, enabling rapid large-scale dispersion in scenarios such as nanofluid preparation, functional coating formulation, and slurry pretreatment, without the need for complex pretreatment steps.
However, the ultrasonic dispersion effect is affected by multiple parameters and requires precise control. Regarding power and frequency, excessive power can easily lead to the breakage of brittle particles. The frequency must be matched to the particle size—small particles (e.g., 10-50 nm) require higher frequencies (500 kHz-1 MHz) to avoid excessive impact. Processing time must be controlled within a reasonable range; excessively long processing times can cause a sudden rise in medium temperature, potentially leading to material denaturation or solvent evaporation. Therefore, a "multiple short-duration ultrasonic" mode is often used. Temperature control requires a cooling system such as a water bath to maintain stable medium temperature. Furthermore, adding surfactants such as SDS and PVP to the dispersion medium can form a protective film on the particle surface, effectively inhibiting secondary agglomeration.
From an application perspective, the advantages and limitations of ultrasonic dispersers are equally apparent. Their non-contact processing method avoids equipment contamination and is highly efficient and quick to operate, making them ideal for laboratory research and small-scale production. However, in large-scale industrial applications, their high energy consumption is a significant issue, and their dispersion effect decreases substantially for systems with a solid content exceeding 30% or high viscosity.
To overcome these limitations, a "multi-technology synergy" strategy is often adopted in practical applications. For example, surface chemical modification of the filler using silane coupling agents can reduce its surface energy and decrease its tendency to agglomerate, followed by ultrasonic dispersion. Alternatively, it can be combined with high-speed shear stirring and ball milling techniques to pre-treat large agglomerates using mechanical force, followed by ultrasonication for fine dispersion. In some applications, a step-by-step "ultrasound + centrifugation" process is employed: ultrasonic dispersion followed by centrifugation to remove undispersed large particles, further improving dispersion quality.
It is important to note that material characteristics must be considered during application: for brittle ceramic nanoparticles such as alumina and silicon carbide, ultrasonic power and time should be reduced to avoid particle breakage affecting performance. Simultaneously, the appropriate dispersion medium must be selected based on the hydrophilic or hydrophobic properties of the filler—hydrophilic fillers are suitable for water-based systems, while hydrophobic fillers require organic solvents, and appropriate additives may be added if necessary. Furthermore, the dispersion effect needs to be assessed by detecting particle size distribution through dynamic light scattering or observing the microstructure using scanning electron microscopy or transmission electron microscopy to optimize ultrasonic parameters.
In summary, ultrasonic dispersers are an efficient means of solving the agglomeration of inorganic nanofillers. With parameter optimization and the synergy of auxiliary technologies, their dispersion advantages can be fully utilized. In the future, with the development of low-energy ultrasonic equipment and the maturity of multi-technology combined processes, their application potential in the industrial field will be further released, providing stronger technical support for the functional applications of nanomaterials.
