Structure, Properties, and Applications of Long-Chain Silane Coupling Agents, Octyltriethoxysilane, CAS Number: 2943-75-1

Structure of Octyltriethoxysilane:The structure of octyltriethoxysilane consists of a long-chain alkyl group (octyl) and a triethoxysilane functional group.

Octyl Part (C8H17): This is a straight-chain alkyl group with 8 carbon atoms, providing hydrophobic characteristics.

Triethoxysilane Part (Si(OCH2CH3)3): This is a silicon-based group connected to three ethoxy groups (-OCH2CH3). Through hydrolysis, it forms silanols (Si-OH), which can further react with the active groups of other materials, enabling crosslinking or coupling effects.

• Chemical Name: Octyltriethoxysilane
• Chemical Formula: C14H32O3Si
• CAS Number: 2943-75-1
• Molecular Weight: 276.49

International Product Comparison Table:

Product Model Supplier

Silquest? A-137 Momentive, USA (formerly GE Silicones)

Z-6341 Dow Corning, USA

OCTEO Evonik, Germany

09835 UCT (United Chemical Technologies, Inc.), USA

Octyltriethoxysilane is one of many long-chain silane coupling agents. Its molecular structure includes an 8-carbon straight-chain alkyl functional group-octyl, along with three hydrolyzable alkoxy groups.

Properties:

• Hydrophobicity and Dispersibility: Octyl imparts excellent hydrophobicity and wetting/dispersing properties. In various applications, it can serve as a water repellent, building protector, and surface modifier for pigments and fillers.

Physical and Chemical Properties:

• Solubility: Soluble in ethanol, acetone, benzene, toluene, and other common non-polar organic solvents. It hydrolyzes in water, and the hydrolysis products easily self-condense into gels, losing efficacy.

Reaction Mechanism: Octyltriethoxysilane is a small-molecule organosilicon compound that can easily penetrate various inorganic materials (such as siliceous stones, concrete, bricks, pigments/fillers, etc.). The silane first hydrolyzes or absorbs moisture from the material or the air, reacting with the water in acidic or basic environments to form hydroxyl groups. At the same time, ethanol, a byproduct of the hydrolysis reaction, is released. These hydroxyl groups condense with the hydroxyl groups present on the substrate to form a stable hydrophobic treatment layer with a three-dimensional network structure, inhibiting moisture penetration into the substrate. In alkaline environments, such as newly poured concrete, the reaction is catalyzed, accelerating the formation of the hydrophobic surface. The octyl group provides hydrophobicity by orienting itself on the surface and inside the material, forming a hydrophobic layer in a certain thickness range.

Preparation of Octyltriethoxysilane Aqueous Solution: To prepare an aqueous solution of octyltriethoxysilane, an organic acid (such as formic acid or acetic acid) is used as a catalyst to adjust the pH of the water to about 3.5 to 4.5. Then, the silane is added and stirred for at least 30 minutes until fully dissolved, resulting in a clear, transparent solution. The concentration of the silane solution should not exceed 2%. Hydrolysis products are unstable, so the solution is recommended for use within 24 hours. If the solution becomes cloudy, it indicates that the silane has partially self-condensed into a polymer (silicone) and lost its effectiveness.

When treating mineral fillers, the silane can be mixed with the minerals under high shear without adding any solvents. After treatment with silane, the treated substrate or mineral surface should be dried briefly at 104-121°C to complete the condensation of silanol and remove the small amount of ethanol formed during the hydrolysis of the ethoxy groups.

Suitable Substrates:

• Includes glass, fiberglass, glass wool, mineral wool, mica, quartz, and other siliceous materials, as well as aluminum hydroxide, magnesium hydroxide, kaolin, talc, steel, zinc, aluminum, and their oxides.
• It is not effective for fillers like calcium carbonate, graphite, carbon black, and barium sulfate, which lack hydroxyl groups on their surfaces.

Applications and Uses:

1. Widely used for waterproofing and seepage control of cement-based and natural stone surfaces, offering excellent water-repellent effects.
2. Used as an additive in cement concrete to improve the impermeability of structures such as dams.
3. Used for surface treatment of various powders, especially titanium dioxide.
4. Used to treat abrasion-resistant carbon black. When combined with precipitated silica in rubber, it can significantly improve the dispersibility of silica.

Solvent Selection for Surface Application: When using octyltriethoxysilane, solvents such as alcohol, carbon tetrachloride, or solvent oils can be used for dilution. Common dilution concentrations are 20% and 40%. If the surface treated with diluted octyltriethoxysilane darkens, it may be necessary to change the type of solvent. Typically, a 40% concentration of octyltriethoxysilane solution can penetrate 3-5 mm into concrete.

Important Notes:

• Ensure sufficient ventilation and fire safety precautions when using any solvent.

Application Methods: When treating materials with an octyltriethoxysilane solution, tools such as spray guns, rollers, or brushes can be used. When using a brush or roller, reapply until the surface remains wet for several minutes. If using a spray gun, continue spraying until the substrate is thoroughly saturated. The spray gun should be equipped with solvent-resistant hoses and gaskets. Before formal application, perform a small-area test to determine the optimal consumption per unit area and ensure compatibility for the best waterproofing effect.

The treated material surface should be free of standing water, dirt, dust, oil, and other contaminants. If necessary, pre-clean the surface and allow it to dry before application. The prepared octyltriethoxysilane solution can be applied to damp surfaces, but dry surfaces ensure maximum penetration into the substrate for optimal results.

Precautions: Products formulated with octyltriethoxysilane provide the best protection when applied to high-alkaline, freshly poured concrete (less than one year old). The effectiveness of protection decreases when applied to old concrete or neutral substrates. It should not be used on structures subjected to hydrostatic pressure.

Avoid application at or below 0°C or in windy conditions, as the solvent will evaporate quickly, reducing effectiveness.

Ensure that plants, animals, and shrubs are not directly or prolongedly exposed to the treatment site, and protect any other materials or substances that should not come into contact with solvents.

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