Reagglomeration

Reagglomeration is the process by which dispersed particles in a suspension, dispersion, or powder reassemble into larger aggregates after partial or complete deagglomeration. It is the reversal of deagglomeration and can occur during milling, drying, storage, or handling when conditions favor particle-particle attraction over stabilization, leading to the reformation of contacts between particles.

The phenomenon arises from interparticle forces such as van der Waals attraction, hydrophobic interactions, and, in some systems, capillary forces from moisture. It is influenced by the stability of the dispersion, which is governed by electrostatic and steric repulsion provided by surface charges, adsorbed layers, or dispersants. Changes in media, pH, ionic strength, or concentration, as well as time-dependent aging and drying, can diminish stabilization and promote reagglomeration. Surface roughness and particle size distribution also play roles, with finer, more reactive surfaces often more susceptible under unfavorable conditions.

Reagglomeration affects a wide range of materials and processes, including pigments in paints, ceramic powders, pharmaceuticals, and nanomaterials. Consequences include increased effective particle size, altered rheology, sedimentation or diking behavior, reduced flow, uneven coatings, and diminished reactivity or processing performance. It can undermine shelf life and product consistency if not controlled.

Prevention and control strategies focus on maintaining stable dispersion: selecting appropriate stabilizers or dispersants to provide electrostatic or steric stabilization; adjusting pH and ionic strength; controlling moisture content; optimizing particle size distribution and solid loading; employing effective dispersion methods during processing; and applying surface modifications to reduce attractive forces. Measurement of stability via zeta potential, dynamic light scattering, rheology, and sedimentation tests helps diagnose and mitigate reagglomeration.