KNOWLEDGE BASE > PRODUCTS > HOW TO PROPERLY DISPERSE NANOPARTICLES OR MICROPARTICLES AND AVOID AGGLOMERATION ISSUES

Dispersing nanoparticles effectively is crucial for maximizing their unique properties in various applications. However, nanoparticles have a high surface area and dangling bonds, making them prone to agglomeration. Agglomeration results in larger particle clusters, which can compromise the nanopowder performance and consistency. For instance, nanoparticles intended to be 50 nm in size might appear as 100 nm or under a Scanning Electron Microscope (SEM) due to improper dispersion techniques. 
The same principles of agglomeration and dispersion apply to microparticles, such as those with particle sizes of 1 µm, 5 µm, or 10 µm, although the degree of agglomeration may vary. Like nanoparticles, microparticles tend to clump together due to Van der Waals forces, surface charge, or insufficient dispersion techniques. To ensure consistent particle size distribution and homogeneity, proper methods such as mechanical agitation (e.g., high shear mixing) or the use of surfactants are essential, particularly when dispersing microparticles in different media.
This comprehensive guide provides step-by-step instructions to help you achieve optimal dispersion of nanoparticles or microparticles, ensuring good homogeneity and preventing common issues like agglomeration.

Additional Offering - We provide ready-made dispersions in various solvents to help bypass the challenging step of dispersion. These pre-dispersed solutions are ideal for research purposes or small quantities, offering convenience and saving time. For larger orders, however, purchasing the nanopowder and dispersing it on-site is often preferred due to logistics and storage considerations. This allows for flexibility in tailoring the dispersion process to specific requirements. You can shop the ready-made dispersions here.

Nanoparticles and microparticles both offer unique properties, but they also present challenges during dispersion:

• Agglomeration: The high surface area and dangling bonds of nanoparticles, as well as the surface forces in microparticles, cause them to clump together, leading to larger-than-expected particle sizes. This is a common issue across all particle types. Improper dispersion leads to larger agglomerates appearing under SEM.
• Surface Reactivity: Both nanoparticles and microparticles can absorb moisture, oxygen, nitrogen, and other substances from their surroundings, affecting stability and dispersion.
• Reduced Wetting Ability: Poor dispersion of nanoparticles or microparticles can result in reduced wetting in solvents, hindering uniform distribution.

Particle Size role:

The smaller the particle size, the greater the difficulty in dispersion. This is because smaller particles have a higher surface area relative to their volume, which increases the strength of attractive forces like Van der Waals interactions. As a result, nanoparticles and fine microparticles are more prone to agglomeration, making them harder to disperse uniformly compared to larger particles.

Morphology role:

The morphology (shape and structure) of nanoparticles and microparticles can significantly affect their tendency to agglomerate. Particles with irregular shapes or high aspect ratios (e.g., rods or platelets) may have more contact points, increasing the likelihood of agglomeration compared to spherical particles. Additionally, flat or elongated particles can create more surface area for attraction forces like Van der Waals to act, further promoting clustering. 

Flaky-shaped particles, such as platelets, have a large surface area relative to their thickness. This increased surface area leads to stronger Van der Waals forces and other surface interactions, which can significantly enhance their tendency to agglomerate. Due to their shape, flaky particles can stack or overlap, making it more challenging to achieve a uniform dispersion. In such cases, specific dispersion techniques like high shear mixing or the use of appropriate surfactants are often necessary to prevent clumping and maintain a stable, homogeneous suspension.

Morphology plays a critical role in determining how particles interact and disperse in various media.

Key Challenges:

• Inconsistent particle size within dispersions.
• Loss of material properties due to agglomeration.
• Difficulty in achieving uniform distribution in various media.

Implementing effective dispersion techniques is essential to overcome agglomeration and achieve good homogeneity. The following methods are widely recognized for their effectiveness:

Ultrasonication is a highly effective method for breaking up agglomerated nanoparticles or microparticles and ensuring good dispersion.

Ultrasonication refers to using high-powered ultrasound waves to create cavitation, which generates intense pressure changes to break apart particle agglomerates. It is more effective compared to general sonication, which often refers to lower-intensity ultrasound, such as in bath sonicators. Ultrasonication is preferred because it delivers higher energy more directly, resulting in better disruption of agglomerates, faster processing times, and more uniform dispersions. It is especially useful for dispersing nanoparticles, where precision and power are required.

• How It Works: High-frequency sound waves induce cavitation, creating microscopic bubbles that collapse violently, generating intense shear forces to break apart agglomerates.
• Best Practices: Utilize probe-type or horn-type sonicators with power ratings between 700W to 1kW. Avoid bath-type sonicators as they are less effective for nanoparticle dispersion. Ultrasonication also aids in degassing the solution, enhancing dispersion quality.

Surfactants play a pivotal role in preventing agglomeration by reducing the attractive forces between nanoparticles.

• Hydrophilic Surfactants: Ideal for aqueous dispersions. Examples include Polyvinylpyrrolidone (PVP).
• Hydrophobic Surfactants: Suitable for oil-based dispersions. Examples include oleic acid.

Additional Offering - We offer a range of surface-treated products specifically designed for this purpose. These treatments, either hydrophilic (e.g., PVP-coated) or hydrophobic (e.g., oleic acid or stearic acid-treated), make dispersing nanoparticles easier in various solvents. The surface-modified nanoparticles or microparticles simplify dispersion and improve stability, especially in challenging conditions. You can find these treated products in our online shop or contact us directly for custom surface treatments tailored to your specific application.

High shear mixing is effective for dispersing nanoparticles or microparticles in various mediums, especially in the oil phase or when mixing with other powders.

• How It Works: High shear mixers apply intense mechanical force, creating turbulence that breaks apart nanoparticle agglomerates.
• Best Practices: Begin by dispersing nanoparticles in water or ethanol with a surfactant (e.g., 1% dodecyl benzene sulfonate). Immediately after mixing, incorporate the dispersed nanoparticles into the target powder (e.g., ceramic powder) and continue mixing at high speeds. Higher stirring rates and longer mixing times improve dispersion quality.

Ball milling is particularly effective for dispersing nanoparticles in dry powder forms and achieving good homogeneity.

• How It Works: Mechanical grinding using balls in a mill breaks apart nanoparticle clusters through repeated impact and shear forces.
• Best Practices: Suitable for dry powders, nanopowders and high-viscosity mixtures. Ball milling ensures thorough blending and uniform distribution but may not be ideal for metal-based nanoparticles due to potential contamination from milling media.

Ball milling is also effective for microparticles. The mechanical grinding process is suitable for breaking up clusters and ensuring good homogeneity for both nanoparticles and microparticles. However, the same precautions apply, such as the potential for contamination when milling metal-based particles. In the case of microparticles, ball milling can help achieve a more uniform particle size distribution, especially in dry powders and high-viscosity mixtures. It remains a versatile method for dispersing various particle sizes.

Coupling agents are essential when creating composites with nanoparticles and microparticles, ensuring strong, conductive interfaces with the matrix.

• How It Works: Coupling agents, such as liquid epoxy, bond nanoparticles or microparticles to the matrix material, enhancing compatibility, electrical conductivity, and mechanical strength. This is especially crucial for achieving stable interfaces in both nanoscale and microscale composites.
• Best Practices: Choose coupling agents based on the matrix material and application. For microparticles, consider factors like particle size and mechanical strength. Proper use ensures robust particle-matrix interfaces, enhancing the composite’s overall functionality.

Heavy metal-based nanoparticles and microparticles often require additional stabilization to maintain suspension and prevent settling.

• How It Works: Stabilizers are added to the suspension to enhance stability and prevent agglomeration in both nanoparticles and microparticles, especially for metal-based particles. For nanoparticles, stabilization is crucial due to their higher surface area, making them more prone to settling.
• Best Practices: Select stabilizers tailored to the type of particle and application. Proper stabilization ensures uniform dispersion and prevents density-related settling, particularly in heavier metal-based microparticles.

The use of stabilizers can apply to other nanoparticles beyond metal-based ones. For example:

• Oxide nanoparticles: Stabilizers can be used to prevent agglomeration and settling, particularly in aqueous dispersions where particles may attract and clump together due to surface charges.
• Polymer-based nanoparticles: Stabilizers help maintain a uniform dispersion and prevent particle interaction or aggregation, which is crucial for applications in drug delivery and coatings.
• Carbon-based nanoparticles (e.g., carbon nanotubes or graphene): Stabilizers can prevent re-agglomeration in suspensions, which is important for maintaining conductivity and mechanical properties in composites.

Stabilizers are essential in many systems where particles tend to settle or agglomerate due to differences in density, surface chemistry, or medium compatibility.

For both nanoparticles and microparticles, pH adjustment can significantly enhance dispersion, particularly for oxide nanoparticles. The pH of a solution influences the surface charge of particles, and adjusting it can reduce attractive forces, such as Van der Waals interactions, or increase electrostatic repulsion, leading to better dispersion. Metallic nanoparticles and polymer-based nanoparticles can also benefit from pH adjustments, especially if their surface chemistry is pH-sensitive. By optimizing the pH, you can improve stability and prevent agglomeration across a range of nanoparticle systems, depending on their surface charge and the dispersion medium.

For oxide nanoparticles, adjusting the pH to neutral (pH 7) can enhance dispersion by reducing particle attraction.

Wet nanopowders are pre-dispersed in a liquid phase, reducing agglomeration and simplifying dispersion in various applications. Pre-wetted powders interact more effectively with the solvent, allowing for uniform distribution and reducing the need for complex techniques like ultrasonication.

Once nanoparticles are crafted, mixing them with water (or another appropriate liquid) immediately helps prevent aggregation. This process stabilizes the particles in suspension by reducing the likelihood of clumping, which can occur if the particles are left dry for too long. By suspending them in water right after production, you maintain their individual dispersion, which makes subsequent processing and applications easier.

• How It Works: Pre-wetted nanopowders are suspended in a liquid phase, which prevents particle interaction and improves compatibility with dispersing mediums.
• Best Practices: Wet nanopowders are highly beneficial for both small and large-scale applications, offering easier dispersion, especially for metal nanoparticles. Additionally, they provide the advantage of simpler shipping and safer handling, as they are not classified as dangerous goods.

Additional Offering - We supply ready-made deionized water-wetted nanopowders, which are especially useful for dispersing in aqueous solutions. These products make dispersion efforts easier, particularly for metal nanoparticles, and come with added benefits such as safer shipping (not classified as dangerous goods) and improved handling safety. Please contact us if you are interested.

Agglomeration is a common challenge. Follow these steps to troubleshoot and resolve agglomeration issues effectively:

• Ultrasonication: Ensure the correct power and duration settings are used to effectively break apart agglomerates.
• Surfactant Addition: Reevaluate the choice of surfactant. For aqueous dispersions, hydrophilic surfactants like PVP are ideal.

• Solvent Selection: Ensure the chosen solvent (e.g., water, oil, ethanol) is compatible with the specific type of nanoparticle or microparticle to achieve effective dispersion.
• pH Adjustment: Adjusting the pH can improve dispersion by reducing particle attraction and enhancing stability. This is particularly important for oxide nanoparticles, but pH adjustment can also benefit other types of nanoparticles, such as metallic or polymer-based particles, when their surface chemistry is pH-sensitive.

• Solid-State Systems: Utilize high-shear mixing or ball milling to physically disrupt and disperse agglomerated nanoparticles/microparticles within solid matrices.

• Heavy Metal-Based Nanoparticles: Introduce appropriate stabilizers to maintain suspension stability and prevent settling. Same for microparticles.
• General Stabilization: Use additives as needed to enhance the overall stability of the nanoparticle dispersion.

• Consistent Mixing: Maintain uniform mixing speeds and durations to achieve even distribution of nanoparticles or microparticles.
• Verification: Use analytical techniques such as SEM or dynamic light scattering (DLS) to verify the dispersion quality and homogeneity.
• Timely Usage: The sooner the dispersed material is used, the better the results, as dispersions can become unstable over time. Delays may lead to re-agglomeration or settling, especially in suspensions, which can impact performance and consistency.

This table provides a comparative overview of various dispersion techniques tailored to various nanoparticle or microparticle scenarios, aiding in selecting the most suitable method for your application.

Effectively dispersing nanoparticles or microparticles is crucial to unlocking their full potential and ensuring consistent performance in various applications. Agglomeration, while common due to particle properties, can be managed with proper dispersion techniques. Methods like ultrasonication, surfactant use, high-shear mixing, and stabilizers for heavy metal-based particles all contribute to achieving stable, homogeneous dispersions. Additionally, coupling agents enhance particle integration into composites, ensuring strong, conductive interfaces. By following the guidelines in this guide, you can overcome dispersion challenges and fully leverage your product's unique properties. For further assistance, feel free to contact us.

This guide was developed in collaboration with researchers actively working in the field of dispersion science and is regularly updated based on their suggestions and findings. Their expertise ensures that the information remains both accurate and practical. We invite those who wish to contribute their knowledge to join the conversation and help advance the understanding of nanoparticle and microparticle dispersion. By sharing your expertise, you can help us improve and expand the content to better serve the community. If you have insights or additional knowledge on dispersion techniques, please feel free to get in touch, and we will incorporate valuable feedback into future updates. Your collaboration is highly appreciated.