How Acrylic Monomers Shape Pigment Dispersion—and Why Flocculation, Floating, and Flooding Occur

In waterborne and solventborne coatings, pigment dispersion is never “just milling.” The stability you see on a drawdown is the result of many small molecular decisions—especially the acrylic monomers chosen for the binder. When those choices don’t match the pigment surface and the dispersant package, pigment flocculation becomes likely, and the same underlying imbalances can show up as floating and flooding.

This article looks at how acrylic monomer chemistry influences dispersion forces, why flocculation in paint happens, and what practical checks procurement and formulation teams can use to reduce risk.

1) Dispersion stability is a balance of forces (not a single setting)

A good dispersion has two requirements:

Wetting: the liquid and resin system must displace air and moisture from the pigment surface.

Stabilization: once particles are separated, the system must keep them separated.

When stabilization is weak, particles collide and stick into loose clusters. That clustering is pigment flocculation. You might still measure the “right” particle size after milling, yet see lower color strength, higher viscosity drift, or reduced gloss because those clusters reform over time—classic flocculation in paint behavior.

Stabilization is usually a combination of:

Electrostatic repulsion (surface charge, often influenced by acid monomers and neutralization)

Steric hindrance (polymer/dispersant chains protruding into the medium)

Acrylic monomers set the binder’s polarity, acid value, hydrogen-bonding potential, glass transition temperature (Tg), and compatibility with dispersants—all of which change whether pigment flocculation becomes a persistent failure mode.

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2) What acrylic monomers change at the pigment surface

Polarity and adsorption

Monomers like methyl methacrylate (MMA) and styrenic components increase hardness and reduce polarity; monomers like hydroxyethyl methacrylate (HEMA) increase polarity and hydrogen bonding. If the binder/dispersant doesn’t adsorb strongly enough on the pigment, the protective layer is thin and pigment flocculation becomes easier. If it adsorbs too strongly in patches (or bridges multiple particles), you can trigger bridging—another route to flocculation in paint.

Acid monomers and surface charge

Acid-functional monomers (e.g., methacrylic acid, acrylic acid) influence:

• pH responsiveness (waterborne)

• zeta potential (electrostatic stabilization)

• interactions with metal-oxide pigments or treated inorganic surfaces

In waterborne systems, insufficient neutralization can reduce charge repulsion and increase pigment flocculation. Over-neutralization can also create issues (excess soluble salts, water sensitivity) while still not fully preventing flocculation in paint if steric protection is weak.

Tg and film formation vs. dispersion stability

Low-Tg monomers (e.g., butyl acrylate, 2-EHA) improve coalescence and flexibility but can change how polymer chains sit at pigment surfaces. A softer, more solvated layer may stabilize well, but it can also be displaced by coalescents or solvents during drying, leading to late-stage pigment flocculation or color movement—often misread as only a drying defect.

3) Why flocculation, floating, and flooding often appear together

Pigment flocculation: the cluster problem

Pigment flocculation is the formation of weak, reversible clusters. Indicators include:

• Lower tint strength than expected

• Rub-up difference (rubbed area looks darker/stronger)

• Increased viscosity over storage

• Loss of gloss or DOI in high-gloss systems

This is flocculation in paint even when the grind gauge looks fine.

Floating: vertical color separation

Floating is a pattern of color non-uniformity (often streaks or mottling) on a drawdown. It can occur when:

• Different pigments in a blend stabilize differently

• Surface tension gradients develop during drying

• Micro-flows redistribute pigment clusters

Because clustered particles respond differently to flow and drying stresses, pigment flocculation can be an enabling condition for floating. Many labs see floating disappear once flocculation in paint is controlled.

Flooding: one pigment dominates the surface

Flooding is when one colorant migrates toward the surface, shifting hue. It’s common in blends (e.g., organic + inorganic) and is driven by:

• Incompatibility among resin, dispersant, and pigment surface treatments

• Changes in polarity during solvent evaporation or water loss

• Differences in particle density and mobility

Again, pigment flocculation can accelerate flooding because flocs move and settle differently than well-dispersed particles, and because dispersion “weak spots” allow one pigment to re-wet and re-distribute during drying—an advanced form of flocculation in paint dynamics.

4) Acrylic monomer choices that commonly influence dispersion outcomes

TJCY supplies acrylic monomers, and our technical team can help assess monomer–pigment compatibility and dispersion-stability risks, including pigment flocculation and flocculation in paint.

5) Mechanisms behind “unexpected” pigment flocculation in acrylic systems

Here are three mechanisms that repeatedly show up when investigating pigment flocculation:

Bridging flocculation

Dispersant or functional binder segments attach to multiple particles at once, tying them together. This is more likely when functional monomers are present but not well-distributed or when dispersant dosage is too low. The result is flocculation in paint that looks like viscosity rise and rub-up.

Depletion flocculation

Excess soluble polymer/dispersant in the continuous phase can create an osmotic imbalance that pushes particles together. This can happen if the acrylic monomer set produces a binder that is highly soluble in the medium, leaving less adsorption on pigment and more “free” polymer—promoting pigment flocculation even though the system seems compatible.

Polarity shift during drying

As water or solvent evaporates, the medium becomes effectively less polar (or more concentrated in certain co-solvents). If the binder formed from your acrylic monomers changes its solvency abruptly, the protective layer collapses and flocculation in paint appears late—often seen as floating or flooding on the panel.

6) Checks that match common buyer/formulator search intent

If you are sourcing acrylic-based binders, monomers, or additive packages, these questions and tests reduce surprises tied to pigment flocculation:

• Rub-up test on drawdowns: fast screen for flocculation in paint in blends and high-strength colors.

• pH and conductivity tracking (waterborne): drift can destabilize charge-based systems and trigger pigment flocculation.

• Viscosity vs. time under heat aging: many flocculation in paint cases show storage thickening.

• Tint strength retention after shear: re-flocculation after high-shear application indicates weak stabilization.

• Pigment-specific compatibility: the same acrylic monomer composition may behave differently on TiO₂, carbon black, phthalo pigments, and iron oxides—each has different surface chemistry and dispersant demand.

• A practical procurement takeaway: request (or generate internally) performance notes on pigment flocculation tendencies across representative pigments, not only a single “standard” color.

Closing thought

Acrylic monomers quietly govern the binder’s interaction with pigment surfaces: adsorption strength, charge, chain conformation, and how all of that changes during drying. When those factors are mismatched, pigment flocculation becomes the “root defect,” while floating and flooding become the visible symptoms. Treating flocculation in paint as a surface-chemistry and drying-path problem—rather than only a milling problem—usually leads to faster, more reliable fixes.