Trouble with ultrafine powder dispersion? We have a dedicated dispersant solution for you, preventing agglomeration and ensuring stable dispersion!
Dispersants play a crucial role in the surface modification of ultrafine powders, primarily improving surface properties, dispersion stability, and subsequent application performance through physical and chemical interactions. Their specific effects can be summarized as follows:
I. Improving Dispersion Stability and Inhibiting Agglomeration: Dispersants adsorb onto the powder surface, reducing its surface energy and weakening van der Waals forces between particles, thereby reducing agglomeration.
Electrostatic Stabilization: Anionic dispersants (such as sodium hexametaphosphate) can increase the zeta potential of the particle surface, forming a double-layer repulsive force, effectively inhibiting the agglomeration of ultrafine nickel powder and other metal particles.
Bergetic Stabilization: Nonionic dispersants (such as polyethylene glycol (PEG) and Tween series) form a physical barrier on the particle surface through their long molecular chains, preventing particles from approaching each other. For example, PEG-1000 can significantly improve the dispersion uniformity of zirconium silicate powder in sol-gel systems.
Combined Stabilization Mechanisms: Some dispersion systems combine electrostatic repulsion and steric hindrance mechanisms. For example, the combined use of sodium hexametaphosphate and polyvinylpyrrolidone (PVP) can prolong the dispersion stabilization time of nickel powder.
II. Regulating Surface Properties and Enhancing Compatibility: Dispersants modify the surface properties of powders through chemical bonding or physical adsorption, improving their compatibility with the dispersion medium:
Hydrophilicity/Hypoperceptibility Adjustment: Titanate coupling agents can form a hydrophobic layer on the surface of zirconium silicate, making it suitable for oily systems; silane coupling agents can introduce organic segments onto the surface of powders such as alumina through surface hydroxyl reactions, enhancing the bonding with the polymer matrix.
Introduction of Surface Functional Groups: Hyperdispersants (such as polyacrylates) typically contain anchoring groups (such as silanes) and solvation segments (such as butyl acrylate). The former binds to the powder surface, while the latter is compatible with the medium, thereby significantly improving the powder's dispersibility in the medium.
III. Synergistic Processing for Optimized Dispersion The selection and application of dispersants directly impact mechanical dispersion efficiency and subsequent processing:
Synergistic Mechanical Dispersion: In processes such as sand milling and high-shear operations, the synergistic effect of dispersants (e.g., oleic acid) and mechanical force can more effectively break down hard agglomerates, reduce energy consumption, and prevent secondary agglomeration.
Media Compatibility: In aqueous systems, polycarboxylate dispersants can influence particle surface charge by adjusting pH; in non-aqueous systems, nonionic dispersants (e.g., the Span series) maintain stability through their solvation chains and compatibility with organic media.
IV. Enhancing Application Performance and Expanding Functional Uses Dispersant-modified ultrafine powders often exhibit superior performance in composite materials:
Enhanced Filling Effect: For example, palmitic acid-modified α-alumina powder disperses more uniformly in polymers, improving material density and mechanical properties.
Imparting or Enhancing Functions: Surfactant-modified (e.g., CTAB)-modified ultrafine zinc powder exhibits better electrochemical stability in alkaline batteries, helping to delay oxidation and self-discharge.
V. Challenges and Selection Principles
Some limitations still exist in practical applications:
Stability and durability issues: Some dispersants (such as polyphosphates) may desorb under drying or high-temperature conditions, requiring combination with surface modifiers (such as silane coupling agents) to achieve long-term stability.
System compatibility requirements: Dispersants must be compatible with the medium and process conditions. For example, some ionic dispersants may fail in high-temperature resins, while the thermal stability of high-temperature resistant dispersants (such as KH550) must be considered.
Summary: Dispersants significantly improve the dispersibility, stability, and application performance of ultrafine powders by adjusting surface energy, introducing functional groups, and synergistic processes. In practical selection, the powder characteristics, media environment, process conditions, and end use must be systematically considered to achieve the best modification effect.
