Every coatings formulator has likely struggled with dispersants at some point: 

❌ Under-dose them, and you suffer from pigment flocculation, hard settling, and rapid loss of fineness. 

❌ Over-dose them, and you trigger severe flooding, floating, viscosity drift, or paint film defects.

It often feels like adjusting an unstable system where nothing works. However, these issues are rarely caused by the quality of the dispersant itself. Instead, they stem from incorrect addition sequences or unbalanced dosage levels that lead to the "deflocculation trap."

From the perspective of colloid and interface physical chemistry, this article breaks down the correct addition sequence, the molecular mechanisms behind dosage failures, and practical formulation rules to achieve ultimate stability.

1. The Correct Addition Sequence: Wetting First, Encapsulation Second

In both laboratory trials and large-scale manufacturing, the order in which raw materials are loaded determines the adsorption efficiency of your dispersant. If this sequence is reversed, the dispersant may never successfully bond to the pigment surface.

A. The Optimal Grinding Feed Method (The Gold Standard for Production)

Before initiating high-speed dispersion or sand-milling, strictly follow this loading sequence:

 Step 1: Pre-mix ─── Add the【Dispersant】into water or the carrier solvent, and stir at low speed until completely homogeneous.   │ Step 2: Pre-wet ─── Slowly charge the dry【Pigment/Filler】powder. Stir at low speed for 5–10 minutes to allow the diluted dispersant to fully wet the powder surface.   │ Step 3: Grind ───── Charge the【Grind Resin/Emulsion】,【Other Additives】, and the【Remaining Solvent/Water】. Start the milling equipment for final dispersion.

• The Advantage: This ensures that the dispersant molecules preferentially and firmly adsorb onto the pigment particle surfaces in the absence of competitive adsorbers (such as high-molecular-weight binder resins). This constructs a complete monomolecular protective layer, maximizing milling efficiency and preventing post-grind shock or agglomeration.

B. Liquid Pre-Dilution Tip

Highly concentrated liquid dispersants must never be poured directly onto dry pigment powders. High local concentrations trigger immediate "polymer bridging," causing the pigment powder to clump into stubborn agglomerates that are extremely difficult to break apart with subsequent mechanical shear. Always pre-dilute the additive with a portion of the reactive diluent, solvent, or water before introducing the powder.

C. Never Add Dispersants Post-Grind

If you discover that the grind fineness does not meet specifications after the milling process is complete, do not attempt to fix it by simply dumping in more dispersant. At this late stage, the system lacks the intensive mechanical shear required to break up stabilized clusters, and free dispersant molecules cannot effectively migrate to wrap around compacted particles. If a post-addition correction is absolutely necessary, you must use a high-shear disperser for an extended period of time.

2. Why Do Both Under-Dosing and Over-Dosing Fail? The Deflocculation Trap

Pigment stabilization in colloidal systems relies primarily on two mechanisms: electrostatic repulsion (charge stabilization) and steric hindrance (spatial shielding). Deviating from the optimum dosage in either direction disrupts this delicate balance.

A. Under-Dosing: Insufficient Shielding, Structural Collapse

When the dispersant dosage is insufficient, the adsorption sites on the pigment surfaces are not fully saturated.

• The Mechanism: The protective barrier is either too thin or incomplete. Under the influence of gravity and van der Waals forces, neighboring pigment particles easily approach one another and re-agglomerate.

• The Consequences: This leads to rapid loss of fineness, hard settling, syneresis, and storage seeding.

B. Over-Dosing: Free Molecules Disrupting Balance (Three Failure Modes)

Formulators often adopt the mindset of "adding a bit more for safety." In colloidal systems, however, excess dispersant is highly destructive:

                    【The Three Disasters of Excess Dispersant】                                      ┌───────────────────────────┼───────────────────────────┐         │                           │                           │  ① Bridging Flocculation      ② Competitive Adsorption        ③ Rheological Instability  Excessive polymer chains on    Once pigment surfaces are sat-  Unbound dispersant molecules   different pigment particles    urated, excess molecules form   free in the continuous phase   interlock with one another,    loose outer layers, thinning    alter the rheology, causing   bridging particles together    the steric barrier. They also   viscosity drift, sagging, and   to cause flooding/floating.    compete with resins, lowering   reduced film hardness by                                  water and chemical resistance.  competing with curing agents.

3. Universal Industry Guidelines for Dispersant Dosage

Because different pigment classes possess vastly different Specific Surface Areas (BET) and polar adsorption site densities, your dispersant dosage must never follow a "one-size-fits-all" approach. Below is the industry-standard starting point for dosages based on active polymer weight relative to dry pigment weight (Active Solid-on-Pigment):

How to Determine the Absolute Optimum Dosage?

We recommend utilizing the Daniel Flow Point Method (Viscosity-Dosage Curve) to run a gradient evaluation:

1. Prepare a series of millbase samples using varying percentages of the dispersant.

2. Grind and measure the initial viscosity of each sample. Plot a curve representing viscosity versus dispersant dosage.

3. Identify the lowest point of the curve (where viscosity is minimized, flowability is optimized, and no flocculation occurs).

4. This point represents your saturation adsorption limit. In actual production, formulate at approximately 110% of this value to allow a safe margin without introducing excessive free molecules.

4. Technical Selection & Co-Formulation Support

When confronting difficult-to-disperse pigments or severe storage stability issues, employing a high-performance polymeric dispersant is key to securing your formulation.

As the flagship wetting and dispersing additive from Tianjin Ruike Chemical Trade Co., Ltd. (Ruike Chemical), RD-9617 High-Molecular-Weight Polymeric Dispersant is engineered specifically for demanding, solvent-borne, and industrial coatings. Incorporating highly efficient anchor groups, RD-9617 firmly binds to inorganic pigments and high-surface-area carbon blacks, building an elastic steric barrier that prevents particles from re-agglomerating. It lowers grind viscosity and guarantees excellent performance under severe cold-heat thermal cycling and centrifugal accelerated settling tests.

If you are currently developing high-end industrial coatings, zero-VOC heavy-duty lines, or high-performance color concentrates, explore our  platform www.rk-chem.com for professional additive solutions.

• Visit www.rk-chem.com to download detailed Technical Data Sheets (TDS) and product guides.

• Contact our technical support team to request a free laboratory testing sample of RD-9617. Let our chemical expertise help your coating systems successfully pass every rigorous stability test!