For fine particles (particle size less than 100 μm), the core of laboratory dispersion is to break inter-particle forces and prevent agglomeration, so as to ensure the accuracy of experiments. The commonly used methods are divided into physical dispersion, chemical dispersion and combined dispersion methods, which are detailed as follows:

I. Physical Dispersion Methods

Widely adopted with no chemical interference, suitable for most particle systems.

1. Mechanical Stirring Dispersion

Principle: High-speed rotation of stirring blades generates shear force to break agglomerates. This method features simple operation and low cost.

Operation Notes: Place particles and dispersion medium into a container, immerse the stirring blades fully in the medium to avoid air bubbles. Set the rotating speed at 500–2000 r/min and stir for 10–60 minutes. For floating particles, moisten them with a small amount of medium first before adding the rest medium.

Application: Systems with slight agglomeration and low uniformity requirements, such as general solution preparation.

2. Ultrasonic Dispersion

Highly efficient for fine particles and heavily agglomerated systems.

Principle: Ultrasonic waves (≥20 kHz) produce cavitation effect, generating impact force and shear force to effectively break agglomerates.

Operation Notes: Place the sample system in an ultrasonic device. Set the power at 200–800 W and treatment time for 5–30 minutes; intermittent ultrasonication is recommended. Insert the ultrasonic probe into the medium, and avoid no-load operation and contact with the container bottom.

Application: Nano-sized particles, heavily agglomerated particles (e.g., nano-oxides) and high-precision experiments such as particle size analysis.

3. Grinding Dispersion

Applicable to ultra-fine and hard-to-disperse particles.

Principle: Collision and friction between grinding media and particles break agglomerates and refine particles, delivering better results than simple stirring.

Operation Notes: Use planetary ball mills or equivalent equipment. Load particles, medium and grinding balls in proper proportions, set the rotating speed at 200–600 r/min and grind for 30 minutes to 2 hours. Remove grinding balls by filtration after treatment.

Application: Hard-to-disperse particles such as ceramic and metal powders, and scenarios requiring particle refinement.

4. Centrifugal Dispersion

Designed for particles prone to sedimentation.

Principle: Centrifugal force disperses agglomerates and resuspends settled particles, ideal for high-density sediment-prone particles.

Operation Notes: Transfer the system into centrifuge tubes, centrifuge at 1000–5000 r/min for 5–15 minutes, then pour off the supernatant or shake the tubes. Combine with ultrasonication for severe agglomeration.

Application: Metal powders, high-density oxides and other sediment-prone systems.

II. Chemical Dispersion Methods

Auxiliary reagents are applied for heavily agglomerated and hard-to-disperse particles.

1. Surfactant Dispersion

Principle: Surfactants adsorb onto particle surfaces to reduce surface tension and form steric hindrance against re-agglomeration.

Operation Notes: Select appropriate surfactants based on particle wettability: SDS for hydrophilic particles and PEG for hydrophobic particles. Add surfactants at a mass ratio of 0.1%–5% into the medium for full dissolution, then add particles and assist dispersion via stirring or ultrasonication.

Precautions: Use proper dosage to avoid interfering with experiments; choose surfactants of suitable grades as required.

2. pH Adjustment Dispersion

Principle: Adjust the pH value of the medium to make particles carry identical surface charges, so as to disperse agglomerates via electrostatic repulsion.

Operation Notes: Regulate pH away from the isoelectric point of particles. For example, alumina (isoelectric point ≈ 9) can be adjusted to pH 5–6 or 10–11. Add dilute acid or alkali slowly to prevent abrupt local pH change.

Application: Charged particles such as metal oxides and hydroxides.

3. Special Dispersant Addition

For specialized dispersion systems.

Principle: Special dispersants (e.g., polycarboxylates) adsorb or react with particles to form a stable dispersion layer and improve dispersion stability.

Operation Notes: Select dispersants according to particle types, add them into the medium at the recommended ratio and dissolve completely, then add particles and perform ultrasonication or grinding for auxiliary dispersion.

III. Combined Dispersion Methods (Physical + Chemical)

For severely agglomerated particles, combined methods deliver optimal performance. Common combinations are as follows:

1. Surfactant pre-treatment + ultrasonication: Soak particles in surfactant solution for 10–20 minutes, followed by ultrasonication. Suitable for nanoparticles.

2. pH adjustment + stirring + grinding: Adjust pH first, conduct preliminary dispersion by stirring, then perform ball milling. Suitable for hard-to-disperse coarse particles.

3. Dispersant addition + ultrasonication + centrifugation: Add dispersant and apply ultrasonication, then centrifuge to remove large agglomerates. Suitable for high-precision experiments.

General Precautions for Dispersion

- Select a medium matching the wettability of particles to ensure effective dispersion.

- Thoroughly clean labware in advance to avoid contamination and experimental interference.

- Optimize parameters for stirring, ultrasonication and other operations to prevent over-dispersion.

- Seal samples for storage after dispersion. Add a small amount of dispersant for systems prone to secondary agglomeration.