Correlation between bulk stresses and interparticle contact forces in fine powders

Area of Science:

• Materials Science
• Powder Technology
• Surface Chemistry

Background:

• Fine cohesive powders, such as xerographic toners, exhibit complex mechanical behavior influenced by interparticle forces.
• Flow control additives, like fumed silica, are used to modify powder properties, particularly adhesion.
• Understanding the relationship between particle-level interactions and bulk properties is crucial for powder processing and application.

Purpose of the Study:

• To investigate the influence of fumed silica concentration on the tensile strength of cohesive powders.
• To correlate bulk powder properties (tensile strength) with interparticle adhesion forces at the single-particle level.
• To explore the role of force chains in the mechanical behavior of these powders.

Main Methods:

• Tensile strength measurements of xerographic toners (12.7 microm particle size) were performed as a function of consolidation stress.
• Atomic force microscopy (AFM) was used to measure the adhesion force between individual particles under varying load forces.
• The concentration of submicron fumed silica additive was systematically varied.

Main Results:

• Tensile strength of the cohesive powders increased with consolidation stress.
• The addition of fumed silica significantly impacted both tensile strength and interparticle adhesion forces.
• A strong correlation was observed between bulk powder stresses and measured adhesion forces between individual particles.

Conclusions:

• Fumed silica effectively modifies interparticle adhesion, leading to enhanced tensile strength in cohesive powders.
• The observed correlation supports the hypothesis of force chain networks governing the bulk mechanical response.
• This study provides insights into the micromechanical behavior of additive-modified powders.