Detection Target
Determination of Dimethicone Content
Overview
Dimethyl silicone oil is a colorless and transparent new synthetic polymer material. It is available in a wide range of viscosities (5 cps to 8 million cps), from highly fluid liquids to thick semi-solid substances. It also exhibits unique properties such as smoothness, softness, and water repellency, along with good chemical stability, excellent electrical insulation, and resistance to high and low temperatures. It has a high flash point, low freezing point, and can be used continuously within a temperature range of -50°C to +200°C. Additionally, it features a small viscosity-temperature coefficient, high compressibility, low surface tension, effective water repellency and moisture resistance, as well as low specific heat and thermal conductivity.
Thanks to its exceptional characteristics, dimethyl silicone oil has gained extremely broad application across various sectors including industrial and agricultural production, national defense, scientific research, and healthcare. It is widely used for electrical insulation, mold release, defoaming, damping, shock absorption, rolling, dust prevention, waterproofing, and humidity control in both high and low moisture environments. Principle An appropriate organic solvent is used to rinse or soak the test sample to transfer the silicone oil on its surface. By utilizing the characteristic absorption band in the infrared spectrum of dimethicone as the measurement wavelength, good accuracy and precision can be achieved.
Apparatus
HKL-FTIR Spectrometer Dedicated to Dimethicone
Instrument Requirements
The wavenumber accuracy must be within ±5 cm-1 near 3000 cm-1 and ±1 cm-1 near 1000 cm-1. The instrument should be calibrated using a polystyrene film (approximately 0.04 mm thick), and its spectrum should be recorded.
(1)Wavenumber Accuracy
Calibration Wavenumber | 3027cm-1 | 2851cm-1 | 1601cm-1 | 1028cm-1 | 907 cm-1 |
Measured Wavenumber | 3025.76 cm-1 | 2850.27 cm-1 | 1600.63 cm-1 | 1027.87 cm-1 | 906.38 cm-1 |
Permissible Deviation | 5 cm-1 | 5 cm-1 | 1 cm-1 | 1 cm-1 | 1 cm-1 |
Actual Deviation | 1.24 cm-1 | 0.73 cm-1 | 0.37 cm-1 | 0.13 cm-1 | 0.62cm-1 |
Compliance | Yes | Yes | Yes | Yes | Yes |
(2) Resolution
Category | Peak Resolution (3110–2850 cm-1) | Depth Resolution (2851–2870 cm-1) | Depth Resolution (1583–1589 cm-1) | Nominal Resolution |
Requirement | 7 peaks | ≥18% | ≥12% | 2 cm-1 |
Measured Performance | 7 peaks | 25% | 18% | 1.5 cm-1 |
Compliance | Yes | Yes | Yes | Yes |
Solution
Attenuated Total Reflection (ATR) Method — Determination of Dimethicone Content
Procedure
Perform infrared spectral scanning of both the sample and reference standard using ATR-FTIR within the wavenumber range of 4000–700 cm-1.
Measure the absorbance at 1259 cm-1 (peak height method).
Calculate the polydimethylsiloxane (PDMS) content in dimethicone using the following formula:
PDMS Content%=100×(Au/As)×(Ds/Du)
Where:
Au= Absorbance of the sample
As= Absorbance of the reference standard
Du= Relative density of the sample at 25°C
Ds= Relative density of the reference standard at 25°C
Application
Applications in the Electromechanical Industry
Dimethyl silicone oil is widely used in motors, electrical appliances, and electronic instruments as a high-temperature-resistant, arc- and corona-resistant, anti-corrosive, moisture-proof, and dust-proof insulating medium. It is also utilized as an impregnating agent for transformers, capacitors, and television scanning transformers. In various precision machinery, instruments, and meters, it serves as a liquid shock-absorbing and damping material. The vibration-damping properties of dimethyl silicone oil are minimally affected by temperature, making it suitable for instruments operating under strong mechanical vibrations and significant environmental temperature fluctuations, such as those in aircraft and automobiles. It is used to stabilize instrument readings, dampen vibrations, and even as a liquid spring in aircraft landing gear.
As a Defoamer
Due to its low surface tension, insolubility in water, and high-boiling-point mineral oils, as well as its chemical stability and non-toxicity, dimethyl silicone oil is widely used as a defoamer in industries such as petroleum, chemical processing, pharmaceuticals, food processing, textiles, printing, dyeing, and papermaking. A concentration of just 10-100 ppm provides an effective defoaming effect.
As a Release Agent
Thanks to its non-stick properties with rubber, plastics, and metals, it is used as a release agent in the molding of rubber and plastic products, as well as in precision casting. It not only facilitates easy demolding but also ensures clean, smooth, and finely textured surfaces on finished products.
As an Insulating, Dust-Proof, and Anti-Mold Coating
When applied to glass or ceramic surfaces and heat-treated at 250-300°C, dimethyl silicone oil forms a semi-permanent waterproof, anti-mold, and insulating film. Treating insulating components with it enhances their insulation properties; applying it to optical instruments prevents lens and prism mold growth; coating medicine bottles extends shelf life and prevents drug adhesion and loss; and treating film surfaces reduces friction, prolonging film longevity.
As a Lubricant
It is suitable for lubricating rubber and plastic bearings and gears. It can also serve as a high-temperature lubricant for steel-on-steel or steel-on-other-metal rolling friction. However, due to its relatively poor lubrication performance at room temperature, it is generally not recommended for ordinary metal-on-metal lubrication.
As an Additive
Dimethyl silicone oil can be added to various materials to enhance their properties. For example, adding a small amount to paint prevents floating and wrinkling while improving gloss; incorporating it into ink enhances print quality; and mixing it into polishing wax (e.g., car wax) increases shine, protects the paint film, and provides excellent waterproofing.
Applications in Healthcare
Dimethyl silicone oil is non-toxic to humans and not broken down by bodily fluids, making it widely applicable in healthcare. Its defoaming properties are utilized in oral anti-flatulence tablets and pulmonary edema defoaming aerosols. Adding silicone oil to ointments improves skin penetration and efficacy. Certain silicone oil-based ointments are effective for treating burns, dermatitis, and bedsores. Its anticoagulant properties allow it to coat blood storage containers, extending blood sample preservation time.
Other Applications
Dimethyl silicone oil has many other uses. For instance, its high flash point, odorlessness, transparency, and non-toxicity make it suitable as a heat transfer fluid in steel, glass, and ceramic industries, as well as in laboratory constant-temperature baths. Its excellent shear stability makes it ideal for hydraulic fluids, especially in aviation. Treating rayon spinnerets with it eliminates static electricity, improving fiber quality. Adding silicone oil to cosmetics enhances skin moisturization and protection, among other benefits.