Why do nanoparticles aggregate?

1.Surface free energy driven mechanism

Nanoparticles have a larger specific surface area and unsaturated surface atoms, leading to an increase in surface free energy. Multi particle contact can reduce the total surface area, release interfacial energy, and thus lower the system's free energy. This trend of energy minimization is the intrinsic thermodynamic driving force behind the spontaneous agglomeration of particles and is a common source of agglomeration at the nanoscale.

2.Static electricity and electrical double-layer instability

The electric double-layer formed by charged particles can provide a stable dispersion state of electrostatic repulsion. When the pH approaches the isoelectric point or the ionic strength increases, the bilayer is compressed, the repulsive force decreases, and the attractive potential energy between particles dominates, leading to agglomeration. The stability of this potential barrier determines the anti aggregation ability of the system.

3.The influence of solvent medium action

Particles in solution rely on solvation shell to achieve interface stability. If the solvent has weak polarity and poor affinity, it is difficult to form an effective solvation layer, which increases the direct contact between particles, enhances van der Waals forces, and triggers agglomeration. Therefore, the physical and chemical properties of solvents directly affect the dispersion state of particles.

4.Chemical binding aggregation mode

Particles with high reactivity can form stable clusters through hydrogen bonding, coordination, or covalent bonding of functional groups such as hydroxyl and carboxyl groups on their surfaces. This chemical bonding makes aggregation irreversible and difficult to physically dissociate. This process is based on the chemical reactivity of surface energy states and functional groups.

Why are nanoparticles dispersed?

1. Establishing a potential energy barrier through electrostatic repulsion

The surface charge of particles will form an electric double layer structure in liquid, and when two particles approach, electrostatic repulsion will be generated between the electric double layers. This repulsive effect can build a potential energy barrier between particles, effectively suppressing aggregation caused by short-range attraction. If there is a sufficiently high potential barrier in the total potential energy of the system, the particles are in a dynamically stable state. This mechanism relies on charge density, dielectric constant, and ionic strength, and is a common stable basis for water-based colloids.

2.Space steric hindrance effect enhancement interval

The steric hindrance effect is generated by the adsorption or grafting of polymer segments on the surface of particles. When particles tend to approach, these molecular structures generate conformational compression and repulsion forces, preventing particle contact.
This mechanism does not rely on surface charge and is suitable for high ionic strength or non-polar systems. Spatial hindrance provides a physical barrier and is one of the most common dispersion mechanisms in polymer coated or surfactant systems, particularly evident in surface modified particles.

3.Solvation shell impedes contact

When particles form a stable solvation layer with solvent molecules, this layer provides significant energy barriers when particles approach, preventing direct contact between particles. The thickness and stability of the solvation layer depend on the polarity, hydrogen bonding ability, and affinity with the particle surface of the solvent. If the contact between particles needs to overcome the desorption energy of the solvation layer, this energy barrier can effectively reduce the probability of agglomeration and is an important dispersion guarantee mechanism under non electric repulsion conditions.

4.Surface functionalization enhances chemical stability

Surface functionalization can introduce charge, spatial structure, or hydrophobic regulatory factors to enhance particle repulsion or improve interfacial compatibility, thereby improving dispersion stability. By grafting ligands, polymer chains, or functional groups, the surface can achieve a dual mechanism of electrical repulsion and spatial protection, making it difficult for particles to approach and form aggregates. This method is widely used in systems such as metal oxides and quantum dots, and is one of the core strategies for achieving controllable dispersion.

SAT NANO is a best supplier of nano powder and micro powder in China, we can supply metal powder, alloy powder, oxide powder and carbide powder, if you have any enquiry, please feel free to contact us at admin@satnano.com