Preface: Water based organosilicon additives are key components in modern coatings, inks, various pastes, and personal care products. The diversity of its performance, from excellent wetting leveling to long-lasting scratch resistance, is determined by its fine molecular composition configuration. From a physical and chemical perspective, it is the result of complex interactions between the organic silicon composition configuration, interfacial thermodynamics, and bulk rheological/mechanical properties.

●  Source of performance differences

Utilize various properties of organosilicon to act on the surface interfaces or cross-linking systems of the slurry, such as substrate wetting, surface leveling, defoaming, etc., based on the flexible migration properties of organosilicon; Using organic silicon to reduce surface energy properties such as smoothness, anti graffiti, wear and scratch resistance; Coupling agents, adhesion promoters, crosslinking agents, dispersants, etc. that utilize the hydrolysis properties of organic silicon. And by modifying the resin with reactive organosilicon containing functional groups, it endows the resin with low-temperature flexibility, smoothness, water and salt spray resistance, and other properties.

The differences in the above performance are the result of complex interactions between organic silicon properties, composition/configuration, interface thermodynamics, and kinetics. This article elaborates on the application mechanisms and basic configurations of 9 water-based organic silicon additives, hoping to be helpful to you.

 

● The Four Main Properties of Organosilicon Chain

① Interface migration

The main chain of polysiloxane exhibits ultra-low rotational potential barrier and ultra long chain segment length, which is the dynamic basis for the interfacial behavior (such as migration and spreading) of organosilicon additives. The Tg of commonly used polydimethylsiloxane (PDMS) is as low as -125 ° C to -120 ° C, indicating strong micro Brownian motion ability at room temperature and all temperatures used in coating applications.

 

② Low surface energy/hydrophobicity

The methyl group (Si-CH3) on the silicon chain has low surface energy/hydrophobicity properties, and during the migration of organosilicon, it extends outward (liquid → gas migration), first migrating to the interface, forming low surface energy (such as PDMS surface tension of about 20-22 mN/m), high droplet angle, and certain demolding properties.

 

③ Thermal stability and chemical inertness

Compared to carbon carbon chains, silicon oxygen chains have excellent thermal stability and chemical inertness. The Si-O bond energy on the organic silicon main chain (about 460 kJ/mol) is greater than the C-C bond energy (about 348 kJ/mol) and C-O bond energy (about 358 kJ/mol). Silicon oxygen chains can be stable for a long time at 180 ° C to 200 ° C and can withstand temperatures above 250 ° C in the short term. By introducing rigid functional groups (such as arylalkyl, polyester, etc.), it can prevent water, ions, and other reactants from approaching and attacking the silicon oxygen bond, and limit the thermal movement of the silicon chain, making it resistant to temperatures of 250 ° C for a long time.

For water-based polyether modified silicone products, due to the limitation of ether bond (- C-O-C -) chain breakage under high temperature and oxygen, their long-term stable working temperature is usually below 150 ° C, and they can tolerate 180-200 ° C in the short term (such as within 30 minutes). It is recommended to use silicone modified polyacrylic esters and other products for water-based high-temperature systems for greater safety.

 

④ Ionic characteristics/hydrolysis

Due to the difference in electronegativity between silicon (electronegativity 1.9) and oxygen (electronegativity 3.5), the Si-O bond at the end has an ionic bond characteristic of about 40%, which can undergo hydrolysis or alcoholysis reactions with OH ⁻ in water, RO ⁻ in alcohol, etc. By utilizing the methoxy (- OCH3), ethoxy (- OC2H5), chlorine (- Cl) and other functional groups on silicon atoms to enhance reaction activity, this characteristic can improve the density of cross-linked networks and anchor/enhance the adhesion of glass surfaces to substrates.

 

●   Configuration and Performance Characteristics of Water based Organosilicon Additives

①  Water based silicone substrate wetting agent

Wetting “is a dynamic process, and wetting agents have small molecular weight and very low static surface tension (21-23mN/m), with high migration and strong surface tension reduction (anti shrinkage/penetration) characteristics. Wetting agents generally act on solid-liquid interfaces, providing lower surface tension than substrates, and can quickly spread low surface energy interfaces (such as plastic and silicone adhesive surfaces).

Waterborne organic silicon wetting agent spreads liquid droplets

Due to the very short organic silicon chain segment of the wetting agent, it cannot form a smooth feeling, and its high mobility also means that it does not affect the recoating performance. A typical water-based trisiloxane wetting agent (such as n=0, m=1), with high migration activity, suitable for stability under pH=6-8 conditions; The larger the n value, the longer the silicon oxygen chain, and the stronger the silicon methyl shielding effect, which can improve the pH tolerance (such as pH=3-12), but the migration activity of rapid wetting will also be correspondingly weakened.

Typical Configuration and Performance Trends of Waterborne Organic Silicon Wetting Agents

It is worth noting that not all wetting agents can exert a wetting effect. Whether they can exert a wetting effect is closely related to factors such as the surface energy of the substrate, construction speed, wet film thickness, and paint film opening time. Moreover, the lower the surface tension, the better. Low surface tension may cause shrinkage and edge shrinkage, and suitable recommendations are very important. The ability to reduce dynamic surface tension is more challenging in high-speed printing/high-speed grinding.

●  Water based organic silicon wetting leveling agent

Compared to wetting agents, wetting leveling agents have a higher proportion of (polyether) modification and longer silicon oxygen chains. By increasing the proportion of ethylene oxide (EO) in the polyether chain segment, the long silicon oxide chains (such as n=10) required for leveling can also have good water compatibility, in order to achieve uniform reduction of surface tension.

Wetting leveling agents can provide lower static surface tension than resins (around 25mN/m, generally higher than wetting agents), with a more uniform ability to reduce surface tension compared to wetting agents, and more action on gas-liquid interfaces.

The essence of leveling is to uniformly reduce the static surface tension of the slurry on the surface (gas-liquid, liquid-solid) through the self migration of organic silicon, which eliminates defects such as orange peel caused by uneven and changing surface tension during drying (Marangoni effect).

Longer silicon segments can provide a smooth feel and scratch resistance, but may also sacrifice instantaneous leveling performance, as well as bring stable foam and recoating/interlayer adhesion issues. Suitable recommendations are crucial.

 

●  Water based organic silicon defoamer

Utilize the incompatibility between silicon oxygen chains and epichlorohydrin (PO) with water to disrupt the bubble membrane. The bubble film of bubbles in liquids is generally formed by surface activity (especially ionic surface activity), and water-based organic silicon defoamers can quickly migrate and act on the gas-liquid interface, promoting the emergence of bubbles and breaking the bubble film.

By adjusting the ratio of epoxy propane (PO) and ethylene oxide (EO) in the polyether modified polydimethylsiloxane defoamer, the HLB value can be controlled to balance the incompatibility and dispersibility of the defoamer with water, such as increasing the proportion of ethylene oxide (EO) to achieve the self emulsification function of the defoamer. The defoaming performance of water-based defoamers can also be improved by adding ultrafine hydrophobic silica defoamers (bentonite/dispersants can be added to reduce silica settling). Unlike polydimethylsiloxane, polydimethylsiloxane has a higher surface tension and does not provide a slippery feel.

The control of corresponding critical compatibility is the key to defoaming, and some defoamers obtained through emulsifier emulsification have the risk of emulsion breaking under high shear (especially in systems containing cosolvents), so suitable recommendations are very important.

 

● Water based anti graffiti additive

Unlike leveling agents, when solvated segments (such as polyethers) are used as the main chain, the organic silicon segments as branch chains have higher degrees of freedom, smaller steric hindrance, and can extend to narrower uncovered spaces. The silicon chains can be well enriched and stacked on the coating surface, resulting in a higher silicon density per unit area of the coating surface, thereby significantly improving the anti graffiti/easy cleaning properties of the coating.

 

●  Water based wear-resistant lubricant

The internally crosslinked microsphere shaped ultra-high molecular weight polysiloxane lotion has better stability on the interface, forms a layer of silicon film through crosslinking, and provides good smoothness, scratch resistance and wear resistance.

This three-dimensional spherical organic silicon is formed by co hydrolysis and condensation of high proportions of trifunctional (T) and tetrafunctional (Q) siloxane structural units in a specific ratio, forming prepolymers with cage, trapezoidal, or cross-linked network structures. The molecular structure is a rigid flexible composite state.

 

●  Water based organic silicon dispersant

The hydrolysis properties of organosilicon can be utilized to anchor on the surface of inorganic pigments and fillers. The hydrolyzed silicon hydroxyl groups can undergo dehydration condensation reactions with the hydroxyl groups on the pigment surface, forming covalent bonds (Si-O-M) with bond energies greater than 400 kJ/mol. Anchoring is very stable and is not easily affected by high temperatures, pH fluctuations, and polar solvent impacts, which can cause desorption.

Excellent wettability, viscosity reduction effect, and long-term stability, especially suitable for stabilizing inorganic nanoparticles with ultra-high specific surface area and surface energy, such as nano iron oxide, nano zinc oxide, nano silicon oxide, and other nanoparticles.

●  Water-based adhesion promoter

Water based adhesion promoters add reactive groups to the resin side or anchor the resin through physical entanglement. At the substrate side, they utilize easily hydrolyzed groups on silicon atoms (such as methoxy (- OCH3)) to anchor on the surface of inorganic substrates (such as glass, ceramics, etc.) through covalent bonds, creating a bridging effect between the substrate and the resin to improve the adhesion of the coating.

 

●  Water based single component PU diplomatic coupling agent

Organic silicone crosslinking agents undergo ring opening reactions with carboxyl groups of waterborne polyurethane resins through their own epoxy groups, and self crosslink to form organic-inorganic hybrid systems, which can significantly improve the water resistance, chemical resistance, and adhesion to inorganic substrates of single component PU paint films.