Trimethoxysilane is a silane compound characterized by the presence of three methoxy groups attached to a silicon atom. This versatile ingredient is primarily used as a surface modifier, coupling agent, and crosslinking agent in various applications, including cosmetics, adhesives, and coatings. In cosmetic formulations, Trimethoxysilane helps improve the adhesion and stability of products while enhancing their overall performance. It is particularly valued for its ability to impart water repellency and improve the texture of formulations.
Chemical Composition and Structure
Trimethoxysilane consists of:
- Silicon Atom: Central to the molecule, providing its silane characteristics.
- Methoxy Groups: Three methoxy (-OCH₃) groups attached to the silicon atom, which contribute to its reactivity and solubility in various solvents.
The chemical structure allows Trimethoxysilane to form strong bonds with both organic and inorganic surfaces, making it an effective coupling agent.
Physical Properties
Appearance: Typically a colorless to pale yellow liquid.
Solubility: Soluble in organic solvents; reacts with water to form silanol.
pH: Generally neutral, compatible with a range of cosmetic formulations.
Odor: Mild, often considered faint or negligible.
Stability: Stable under normal storage conditions but sensitive to moisture, which can lead to hydrolysis.
Production Process
Synthesis: Trimethoxysilane is synthesized through the reaction of silicon tetrachloride with methanol or by other methods involving silicon compounds and methanol.
Purification: The product is purified to remove any unreacted materials and by-products, ensuring a high-quality ingredient.
Formulation: Purified Trimethoxysilane is incorporated into various cosmetic products to enhance their adhesion, stability, and performance.
Applications
Medical: Occasionally used in topical formulations for its ability to enhance product stability and adherence to the skin.
Cosmetics: Commonly found in primers, foundations, and other makeup products for its film-forming and water-repellent properties. It improves the texture and longevity of cosmetic applications.
Industrial Uses: Employed in adhesives, sealants, and coatings for its coupling and crosslinking abilities, enhancing durability and performance.
Environmental and Safety Considerations
Trimethoxysilane is generally regarded as safe for use in cosmetics when applied according to recommended guidelines. It is well-tolerated by most skin types, but appropriate handling and storage are essential due to its sensitivity to moisture.
Responsible sourcing and formulation practices are necessary to ensure that the ingredient is free from harmful contaminants and produced sustainably.
References__________________________________________________________________________
Krasnoslobodtsev, A. V., & Smirnov, S. N. (2002). Effect of water on silanization of silica by trimethoxysilanes. Langmuir, 18(8), 3181-3184.
Abstract. Water has a big influence on the mechanism of monolayer formation and therefore on the structure of monolayer that can be obtained on a silica surface. Trimethoxysilane in the absence of water can form submonolayers with only one siloxane bond binding functional tails with the surface. We show here that hydrolysis of the remaining methoxy groups on the initial immobilized silane layer by water and followed by another silanization yields enhanced surface density of silanes with improved lateral polymerization and without complications of vertical polymerization. The improved technique allows surface concentration of coumarin dye molecules of 2.7 × 1014 cm-2, almost 1.3 times higher than what is possible without water treatment.
Finocchio, E., Macis, E., Raiteri, R., & Busca, G. (2007). Adsorption of trimethoxysilane and of 3-mercaptopropyltrimethoxysilane on silica and on silicon wafers from vapor phase: an IR study. Langmuir, 23(5), 2505-2509.
Abstract. The interaction of trimethoxysilane (TMS) and of 3-mercaptopropyltrimethoxysilane (MPTMS) with silica and silicon wafers has been studied by the mean of transmission FTIR spectroscopy. TMS vapor adsorption on silica's silanols results in the formation of Si−O−Si bonds at room temperature, mainly through the elimination of one methanol molecule per TMS molecule. Similarly, MPTMS vapor reacts with the surface through “hydroxolysis” of one of Si−O−CH3 bonds, and most of the molecules have their SH group free. The same species is formed over the silicon wafer surface. On the other side, deposition of liquid MPTMS over silicon surface leads to the detection of spectral features characterizing a condensed layer.
Innocenzi, P., Brusatin, G., Guglielmi, M., & Bertani, R. (1999). New synthetic route to (3-glycidoxypropyl) trimethoxysilane-based hybrid organic− inorganic materials. Chemistry of materials, 11(7), 1672-1679.
Abstract. Hybrid organic−inorganic materials have been obtained by cohydrolysis of (3-glycidoxypropyl)trimethoxysilane (GPTMS) and tetraethyl orthosilicate (TEOS) in acidic conditions. Boron trifluoride diethyl etherate (BF3OEt2) has been used to catalyze the epoxide polymerization. The effect of BF3OEt2 has been studied by multinuclear magnetic resonance (NMR) in the precursor sol and by Fourier transform infrared spectroscopy in the final material. The addition of BF3OEt2 to a prereacted sol of GPTMS and TEOS has allowed the epoxide ring opening at room temperature, without formation of diol units or boric acid precipitation in the final material. The prereaction time of GPTMS with TEOS has been found to be an important parameter. The catalytic effect of BF3OEt2 with respect to other commonly used catalysts in sol−gel processing of GPTMS-based hybrid organic−inorganic materials, such as zirconium butoxide and 1-methylimidazole, has been studied.
Trimethoxysilane 
Methoxy Groups
