Different Types Of Silicone Oil And Their Applications

Over the years, silicones have become the most popular man-made compounds for applications ranging from medicine and cosmetics to insulation. This inert compound comes in various forms such as silicone oil, resin, rubber, grease, etc. Here, we will focus on silicone oil. Silicone oil is a synthetic material composed of silicon, oxygen, hydrogen, and elements required for special properties. It has high oxidation stability, chemical inertness, and viscosity stability. Its excellent and continuously expanding performance makes it suitable for more application scenarios. 

Below we will introduce silicone oil definition, types, manufacturing steps, applications, etc. You can learn more useful information and some of the significant advantages and disadvantages of this polymer from this article.

What is silicone oil?

Silicone oil is a liquid silicone polymer containing organic groups at both ends and all side chains. The structural form of these polysiloxanes can be linear, cyclic, or branched. The most commonly used linear polymer is polydimethylsiloxane, also known as PDMS, and other silicone polymers are its derivatives. In some cases, any side chains and termini in the polydimethylsiloxane molecule can provide bonding sites for other organic groups to bond with the silicon to create more variants and obtain new beneficial properties and reactivity. Commonly introduced groups are vinyl, phenyl, amino, trifluoropropyl, hydroxyl, epoxide, and hydrogen. These polysiloxane compounds typically offer high rheology, and temperature resistance properties under extreme environmental conditions.

Molecular structure of Silicone oil

Silicone oil with a unique chemical structure is composed of multiple repeating units of silicon (Si) and oxygen (O) atoms, with oriented and soft helical polysiloxane chains. The remaining valence states of silicon combine with various organic groups to form tetravalent organosilicon compounds. They are mainly methyl (-CH3). In addition to being commonly used as a raw material for silicone rubber and other materials (plastics, rubber, etc.), ordinary dimethyl silicone oil can also be made into effective application modes through special formulas to produce specific effects. Introducing different functional groups (amino groups) into the PDMS molecular chain to replace a small part of the methyl group changes the way the siloxane chain interacts with the polymeric chains of other materials. By adding appropriate chemical functional groups to the siloxane polymer to react with other polymers, the surface properties of the material can be modified. Modified allows silicone polymers to be integrated into various types of organic polymers, and even creates new specific properties such as toughness, impact strength, smoothness, and mold release.

The number of Si-O bonds in silicone oil molecules is the degree of polymerization, generally expressed by n, ranging from a few to several thousand. The degree of polymerization mainly depends on the reaction conditions (temperature, time, catalyst type) and material selection (silane precursor). Depending on the variant, the properties and molecular structure of the material can be tuned by changing the chain length, degree of branching, and cross-linking, which allows these polymers to be used in many products including cosmetic ingredients, drug delivery systems, adhesives, lubrication agent, defoaming agent, antistatic agent, emulsifier.

How is silicone oil made?

Silicone oil consists of any organic side chains attached to a siloxane chain. The basic steps for silicone oil manufacturing are as follows:

Step One: Raw Material Preparation

After extracting commercially valuable metallic silicon from rocks or sand, the ground silicon powder is evenly mixed with methyl chloride gas and subjected to a series of reactions under high temperature and catalyst (copper) conditions to convert it into methylchlorosilane. Dimethyldichlorosilane is then synthesized through three steps of hydrolysis, decomposition, and condensation of chlorosilanes, finally, dimethyldichlorosilane is hydrolyzed and cracked to obtain the basic raw material of organic silicon (DMC, D4).

Step 2: Synthesis

The dimethylsiloxane oligomer is uniformly mixed with a catalyst, stabilizer, and other additives and polymerized under a certain temperature and pressure to obtain a siloxane mixture.

Step 3: Separation and Purification

The purity of silicone oil is improved by removing unreacted residual impurities (stabilizers, catalysts) in the mixture through distillation, filtration, and crystallization methods.

Step Four: Tune Performance

The base polymer is modified through various chemical processes and different additives to meet the specific properties required by the application, such as viscosity, flow, mechanical properties, oxidation resistance, and insulation properties. These silicone polymers are processed into the final product.

Step 5: Packaging and Storage

Final processed silicone oil is usually packaged in iron drums and plastic drums with strict standards to ensure that its quality remains stable under long-term storage and different transportation methods.

Types of silicone oil

The types of silicone oil can be classified according to the different substituent groups on the polysiloxane chain. Please see below for details:

Classified by group, the groups of silicone oil can be methyl, phenyl, hydrogen, and other organic groups. This classification includes the following terms:

Methyl and Methyl groups - also known as Methyl silicone oil/Dimethyl silicone oil/Dimethicone/Dimethylsilicone fluid/Dimethicone. They are the most classic products among silicone oils, especially used the most in industrial lubrication. They are also the first developed basic silicone oils with a high viscosity index and low surface energy.

Methyl and Phenyl groups - also known as Methylphenyl Silicone fluid/ Methylphenyl Silicone oil/ Phenylmethylsilicone/ Polymethylphenylsiloxane/ Phenylpolysiloxane. Compared with ordinary methyl silicone oil, they have better radiation resistance, temperature resistance, compatibility, chemical resistance, and oxidation resistance.

Methyl and hydroxyl groups- also known as Dimethylhydroxy silicone oil/ Hydroxyl silicone oil/ Hydroxyl-terminated polysiloxane. This type of silicone oil is commonly used because the hydroxyl group can undergo a condensation reaction with other compounds in the presence of a catalyst to form new silicone compounds.

Methyl and Vinyl groups- also known as Vinyl silicone oil/ Methyl vinyl silicone oil. It shows better waterproof and lubricating properties under high temperatures and harsh environments. It is also known for its simple synthesis process and high yields.

Methyl and hydrogen groups - also called Methylhydrogen Silicone oil/ Hydrogen silicone oil. It is known for its excellent reactivity and hydrophobic properties.

Methyl and Fluoroalkyl groups- Methyl and Fluoroalkyl are also known as fluorosilicone oil/ Trifluoropropyl silicone oil/ Methyltrifluoropropyl polysiloxane. They have higher resistance to various chemical solvents, fuels, and chemicals.

Silicone oils are classified not only according to their carbon-based substituents but also according to their dynamic viscosity value (25C°) or the average number of siloxane groups. Generally speaking, there is a tolerance on the viscosity of silicone oil, which ranges from +/-10%.

Advantages and Disadvantages of Silicone Oil

While the performance advantages of silicone fluids make them excellent in extreme temperatures and chemically demanding applications, their disadvantages also drive development engineers to continually improve and create variants with greater versatility.

Advantages

High thermal oxidative stability

Some silicone oils have excellent oxidation resistance. They can maintain their stability after being exposed to temperatures up to 250 °C for a long time and are not prone to decomposition and oxidation. Silicon-oxygen bonds in the polymer chain provide excellent heat resistance.

Excellent viscosity stability and shear resistance

Viscosity stability and shear resistance are two outstanding properties of silicone oils. Based on its chemical structure, this material exhibits little change in viscosity upon continuous exposure to a wide range of operating temperatures (-76°F to 392°F). It resists shear stress that may cause thickening or thinning under extreme conditions. Its shear resistance is more than 20 times that of other organic petroleum. These are important for hydraulic systems and pharmaceutical applications where accuracy is critical.

Compressibility

Because the helical chains between silicone oil molecules easily slide against each other, silicone oil can maintain fluidity and lubricity under harsh environments of high pressure, high load, and high temperature for a long time. When the external force is removed, they will return to their original shape. Compared with ordinary insulating oil, mineral oil, or other organic compounds, silicone oil has higher compressibility.

Low surface tension and high spreading ability

Silicone oil has low surface tension. For example, polydimethylsiloxane has a lower surface energy than carbon paraffins. Its surface tension is lower than ordinary oils, surfactant aqueous solutions, or water. The repulsive effect of methyl groups makes it easier to spread on the surface of various substances.

Chemically inert

Silicone oil exhibits low reactivity under many conditions. It is not attacked by most chemicals and solvents, including oxidants, alkalis, and acids. IIt is also poorly soluble in water, ethanol, and methanol, and does not react with most organic polymers. Gelling may occur only in long-term contact with lead, tellurium, and selenium. 

This liquid polymer also has good self-extinguishing properties and significant mold release, water repellency, insulation, biocompatibility, and natural aging (UV).

Disadvantages

Poor biodegradability

Because silicone oil has a stable polymer structure, so its degree of biodegradation is very low. Its long-term and large-scale use will leak into the soil to form a dense film, which may affect the survival and reproduction of plants and microorganisms in the soil.

Poor boundary lubrication

One of the factors limiting the use of silicone oil: Compared with other synthetic lubricants, silicone oil exhibits poor boundary lubricity at certain metal (steel-steel) interfaces.

Difficult to clean

Due to its non-polar nature, silicone oil is not miscible with water or soap. After use, a layer of oil film that is difficult to clean often remains on the surface of the equipment or human body, which requires the use of a special detergent solution to clean it.

Applications of Silicone Oil

Silicone oil is a multi-viscosity, multi-functional, multi-purpose material. Because it can operate normally under harsh operating conditions with little change in viscosity, it has many key functions in various fields and sectors. Here are some common applications for silicone oil:

Lubricant

Common lubricants are manufactured using silicone oil and have a variety of applications in industry. Silicone oil is viscosity stable and resistant to chemical solvents, making it ideal for use in environments with wide temperatures or harsh chemicals. Since silicone oil provides good protection and lubrication for metal-on-metal and plastic-on-plastic combinations, it is often used to lubricate mechanical parts including various bearings, gears, conveying systems, and other types of components. But for steel-on-steel combinations, it Exhibits poor boundary lubrication properties.

Release agents and anti-stick agents

Silicone release agents are used in applications ranging from plastics, rubber, and metals to food, and excel in improving product quality as well as improving operational efficiency. In addition to direct use, silicone oil is also used as a release agent in the form of grease, solution, or emulsion to suit different purposes. It provides a non-stick, chemical-resistant, heat-resistant protective coating. It prevents a variety of molding materials from bonding to the mold during high-temperature, high-pressure processing without transferring to the parts being processed. This is because it bonds to the surface of the mold to form a coating that is easy to release and does not break down easily, so parts can be released quickly without contamination or damage to the mold. Silicone oil also provides long-term anti-stick protection for paper products as well as metal forging applications.

Defoaming agents

Silicone oil has low solubility (such as water and general oil), no physiological activity, and high surface activity, so it is very suitable for chemical, pharmaceutical, beverage and food industry applications that enter the body. Compared with other defoaming agents, silicone defoaming agents are more durable and provide faster and more effective foam reduction services, even improving product quality.

Shock absorbing oil and damping oil

Silicone oil is often used as shock-absorbing oil and damping oil. They are vital for components in cars, ships, and aircraft. Its extremely high compressibility, thermal stability, weather resistance, and corrosion resistance allow it to be used and perform well in these demanding areas. As anti-shock oil and filling oil, it can ensure the output signals and pointer readings of various instruments are stable and reliable.

Electrical insulation

Silicone oil is a near-perfect insulator and is commonly used in various types of insulators, transformers, cables, sheaths, and circuit breakers. Its extremely high dielectric strength and heat dissipation properties enable it to insulate, arc-extinguish, and cool high-voltage equipment under extreme climatic conditions that may cause oxidation or breakdown of other materials. Silicone insulating oil always maintains a stable dielectric constant, flexibility, high flash point, and waterproof to ensure safe and reliable operation of sensitive equipment.

Heat carrier

Some silicone oils are used as heat carriers in the presence of high temperatures. They are very popular in petrochemical equipment, plastic extruders, and rubber vulcanization equipment. They also act as a cooling medium, transferring heat from the car's engine to the radiator of the water tank.

Polishes and surface treatments

Silicone brighteners, polishes, and surface treatments provide glossy, hydrophobic, and weather-resistant finishes for furniture, automotive tires, leather goods, plastics, and rubber applications.

Cosmetic

Silicone oil is widely used in cosmetics such as foundation, sunscreen, skincare, hair care, and makeup. Its stretchability, breathability, and non-allergenic properties provide skin with comfort, smoothness and shine. Its volatility allows it to be used as an active ingredient in deodorants, antiperspirants, shampoos, and body washes.

Food processing

Food-grade silicone oil processed with long-term contact with food complies with relevant FDA regulations. High safety, odorless, and light transmittance are regular requirements in the food field. Its high biocompatibility, temperature stability, and chemical stability enable it to not only meet strict hygiene standards and ensure no contamination and damage to food and processing equipment but also improve production efficiency and food safety.

Conclusion

Silicone oil is a high-performance polymer with an unparalleled combination of properties and is known for its excellent dielectric properties, heat resistance, low surface tension, ductility, softness, etc. Due to these unique properties, silicone oil has become a commercially valuable polymers.

Yongrui is a leading global silicone oil manufacturer. Our team has extensive experience in the production of ordinary and modified silicone oils and can provide your project with the performance and viscosity you require. For any silicone oil questions, our engineers will provide effective suggestions and final solutions based on your usage environment and purpose.