Differences Between Dispersants and Wetting Agents and Their Combined Use
1. Why Are They Often Selected Separately in Formulations?
In waterborne coatings, pigment pastes, and concentrated pastes, powders (pigments, fillers, graphite, carbon black) go through the full sequence of wetting-out → milling → dispersion → storage → application. Solving only one part of the process will cause problems to surface in the next:
- Adding only a wetting agent: Initial wetting is fast and fineness is easily achieved, but particles lack sufficient repulsion; after standing, flocculation and sedimentation occur, and the flocculation point of the paste increases.
- Adding only a dispersant: Particle repulsion is adequate, but if the powder is hydrophobic, the aqueous phase cannot spread over it, making milling time longer — even causing agglomeration when more dispersant is added.
- Using both: The wetting agent is responsible for wetting the particles and reducing the solid-liquid interfacial energy, while the dispersant builds a stable adsorbed layer on the particle surface, providing electrostatic/steric repulsion.
Key judgment: To determine which component is missing, observe two phenomena — “difficulty in achieving fineness and long milling time” mainly indicate insufficient wetting; “fineness meets spec but flocculation, floating, or flooding occur after storage” mainly indicate insufficient dispersion.
2. Mechanism Comparison: Who Does What?
| Aspect | Wetting Agent | Dispersant |
|---|---|---|
| Primary function | Reduces solid/liquid and liquid/gas interfacial tension, promotes spreading | Adsorbs on particle surface, provides electrostatic/steric repulsion |
| Target | Powder particle surface, substrate surface | Between particles |
| Key indicator | Static/dynamic surface tension, foam height | Zeta potential / particle size stability, flocculation point |
| Effective stage | Early wetting and milling | Whole dispersion and storage process |
| Failure symptoms | Slow wetting, cratering, inability to achieve fineness | Flocculation, sedimentation, floating/flooding |
| Typical types | Acetylenic diols (low foam, low tension), polyethers, silicones | High-molecular-weight dispersants (DS/ADS/HD series), low-molecular-weight dispersants |
In a nutshell: A wetting agent “delivers water to the particle surface”; a dispersant “keeps particles separated and prevents agglomeration” — the first half of the process depends on wetting, the second half on dispersion.
3. Combination Approach: Synergy of Three Toynol® Product Lines
Three relevant product lines are available on the Toynol® website and can be combined by scenario (specific product suitability and dosage refer to the TDS):
| Scenario | Primary wetter (low foam, low tension) | Secondary wetter/solubilizer | Dispersant | Key monitoring indicators |
|---|---|---|---|---|
| General waterborne coatings/pastes | FS-204 (acetylenic diol) | Superwet-320/360 | DS-192M / DS-194 / ADS-20 | Fineness, foam height, flocculation point |
| Severe foaming during milling | FS-204 | Use less or none | DS-255 / DS-195H | Defoaming speed, compatibility |
| Wetting low surface energy substrates | FS-204 | Superwet-4000/4100A | Select based on system | Cratering, adhesion |
| Difficult-to-disperse powders (graphite, carbon black, etc.) | FS-204 | Per lab trial | HD-20 / HD-23 | Particle size D90, sedimentation after 7 days storage |
Key points for combination:
- Acetylenic diols (FS-204 series): Combine low foam with low dynamic surface tension; often used as a starting point for combined wetting/dispersion (0.1% aqueous solution dynamic surface tension: 33.3 dyn/cm, refer to TDS for exact value);
- Superwet series: Added when a single strong wetting/solubilization requirement exists, to solve cratering on low surface energy substrates (plastics, coated panels);
- DS/ADS/HD dispersant series: Added when strong dispersion and long-term stability are required; Zeta potential and flocculation point are key verification indicators;
- Order of addition: Generally add the primary wetter first to wet the powder, then add the dispersant to build the adsorbed layer; mixing intensity and shear time should be determined by lab trial.
For cross-reference to BYK Disperbyk / Evonik Surfynol equivalents, please refer to the information publicly available on the Tianjin Hi-Perferal Advanced Materials Co., Ltd. website, and request a cross-reference table from the supplier.
4. Common Pitfalls
- Treating the two as interchangeable: Adding only a “dispersant” leads to slow wetting; adding only a “wetting agent” leads to flocculation — ask first which stage the system is stuck in when selecting.
- Overdosing: Excessive amounts of either type increase viscosity, cause emulsion breaking, and affect film formation. Start at 0.1% and conduct gradient lab trials.
- Looking only at static surface tension: When selecting or qualifying, request dynamic surface tension data (bubble method), otherwise it may not meet milling conditions (refer to TDS).
- Neglecting storage stability: Meeting fineness spec does not guarantee long-term stability. Re-test particle size and sedimentation under high temperature, high shear, or very dilute systems.
- Directly mixing with silicones: Compatibility is poor. Add separately, control order and mixing intensity.
Frequently Asked Questions (FAQ)
Q1: Can only one of dispersant or wetting agent be used?
A: It is possible but not recommended. If the system has both “poor powder wettability” and “easy particle flocculation”, using only one often solves one problem at the expense of the other. It is recommended to start with an acetylenic diol as the primary wetter and a dedicated dispersant in a lab trial.
Q3: When the paste flocculation point is large, which one should be added first?
A: A large flocculation point indicates insufficient dispersion. Add or switch dispersant (DS/ADS series) first. If at the same time milling time becomes longer or fineness is hard to achieve, then add a wetting agent in addition.
Q3: Is Toynol® FS-204 a dispersant or a wetting agent?
A: It is an acetylenic diol often used as a combined wetting + dispersing additive (low foam, low dynamic surface tension). For strong dispersion and long-term stability needs, it is recommended to add DS/ADS series dispersants in lab trials.
Q4: How to solve cratering on low surface energy substrates (plastic/coated panels)?
A: The root cause is insufficient wetting combined with dynamic tension gradient. It is recommended to use FS-204 as the primary wetter combined with Superwet-4000/4100A in a lab trial, and control substrate cleanliness and drying. The specific solution depends on the formulation trial.
Q5: Is the correct selection sequence “scenario → indicator → lab trial → confirm dosage”?
A: Yes. Do not directly set 0.5% based on experience. First identify whether the bottleneck is wetting or dispersion, then start with the dosage as per the TDS gradient, and determine the final dosage by evaluating fineness, foam height, and flocculation point.
Core Conclusions
- Wetting agents address “spreading”, dispersants address “stability” — they complement each other, not replace one another; using only one often leads to trade-offs;
- To judge which is missing: inability to achieve fineness / long milling time → insufficient wetting; fineness acceptable but flocculation upon storage → insufficient dispersion;
- Recommended combination: acetylenic diol (FS-204) as primary wetter + Superwet series for assistance + DS/ADS/HD dispersants based on scenario, start with a 0.1% gradient lab trial;
- Three key indicators to verify: fineness (D90), foam height, flocculation point / sedimentation after 7 days storage;
- Data source: specific product performance, dosage, and pH window should be based on the TDS from Tianjin Hi-Perferal Advanced Materials Co., Ltd.; cross-reference information should follow the public data on the official website.
