What Are Silicones?
Silicones are polymers that are also known by the name polysiloxanes. These are the polymers that involve any inert, synthetic compound made up of iterative units of siloxane. It is a chain of alternating oxygen and silicon atoms that are frequently combined with hydrogen and carbon.
Silicons are the present-time class of synthetic objects and contribute to thousands of applications that offer safety and well-being in everyday life. Silicones are further a diverse family of high-performance materials that include silicone fluids, silicone polymers and reactive silanes. These materials are widely used in a variety of industrial and consumer products, and they provide essential benefits in various areas, including personal care, health care, aerospace, transportation, electronics and construction.
Composition and Structure
The silicones are different from many industrial polymers, where the chain of atoms that build the backbones of their molecules does not include carbon, being a characteristic member of organic compounds. The absence of carbon makes silicone a unique polymer, though maximum members of class II organic groups such as methyl(CH3) and vinyl(CH2) are linked to every silicon atom. Alternatively called polymerized siloxanes or polysiloxanes, silicones have an inorganic silicon-oxygen backbone chain (⋯−Si−O−Si−O−Si−O−⋯), where two organic groups are attached to each silicon centre.
The general formula of silicone is (R2SiO)x, where R belongs to any one of the organic groups.
Poly-dimethylsiloxane is the most silicon compound, which illustrates the primary characteristics of the organic class. The first substance is metallic silicon, obtained from silica sand. The silicon reacts with methyl chloride (Ch3Cl) and forms dimethyldichlorosilane ([CH3]2Si[Cl]2) over a copper catalyst. When this compound is made to react with water, the atoms of chlorine get replaced by hydroxyl groups(OH). The resulting compound, silanol ([CH3]2Si[OH]2), polymerizes in a condensation reaction. Every individual unit of molecules links together to form poly-dimethylsiloxane with associated loss of water.
Properties of Silicones
Some of the common properties of silicones are as follows:
- Silicones have low thermal conductivity and chemical reactivity.
- Their toxicity is also low.
- It can repel water and form watertight seals.
- It has high resistance to oxygen, ozone, and ultraviolet (UV) light.
- It has both electrically insulative and conductive properties.
- It has high gas permeability and high thermal stability
- They are superior solvents for organic compounds.
If silicone is burned in the presence of oxygen, solid silica (silicon dioxide, SiO2) is formed as a white powder as well as char and various gases. This white powder is often called silica fume.
Preparation of Silicones
Silicones are usually prepared from pure silicon that is obtained by the reduction of silicon dioxide (silica) in the form of sand with carbon at high temperatures:
SiO2(s) + 2C(s) → Si(s) + 2CO(g)
Generally, silicones are produced from silicon in three stages:
a) Synthesis of chlorosilanes
b) Hydrolysis of chlorosilanes
c) Condensation polymerization
When silicone is burned in the presence of oxygen, solid silica (silicon dioxide, SiO2), white powder, char, and various gases are formed. The readily dispersed powder is sometimes called silica fume.
Applications of Silicones
Silicones can acquire many forms, from liquids to solids, that allow engineers, inventors, and companies to use them as key components in various industrial applications. It is their versatile quality that makes silicones an essential ingredient in products that make our lives better, whether as rubbers, fluids, resins, silicone gels or silicon glue. Silicones can be found in a different number of applications, starting from computers and engineered spacecraft, shampoo, to baking moulds. Silicones can also be consumed in renewable energy, starting from wind turbines to solar panels, relying on silicone technology.
Personal Care Products
Silicones are widely used in personal care products. They are used to reduce the white residue and tacky feel of antiperspirants in deodorants. Silicones are used in cosmetics, shampoos and conditioners to retain the colour and lustre of the compound. Silicones have been said to offer better shine, and skincare products can be made with stronger SPF.
Construction Materials
Silicones are used extensively as a construction material for erecting commercial and residential buildings. They are said to prevent damage from moisture and bacteria build-up.
Electronics
Silicones can be found in keypads, keyboards and copier rollers. Many other components of computers, mobile electronics and home entertainment equipment make use of silicones. LED lighting technology is made possible by silicones. It has high thermal stability and excellent dielectric properties. So, it is used in a variety of electrical transmission applications.
Solar Panels and Photovoltaic Devices
Silicones are ideal materials that are used to improve the efficiency, durability and performance of solar panels and photovoltaic devices. They can basically withstand the sun for years.
Aviation Industry
Due to its high stress and temperature resistivity, silicone adhesives and sealants are practically used to seal and protect many parts of an aeroplane. It is used as a sealant in windows, doors, overhead bins, fuel tanks, engine gaskets, hydraulic switches, wings, wing edges, landing gear, electrical devices, vent ducts and even in black boxes.
Kitchenware
Silicone bakeware and cookware are available widely and used in the kitchen to prepare different dishes. These utensils do not affect food taste or quality.
Paints and Coatings
Today, there are silicone-enhanced paints available in the market. These types of paints help to keep the exterior coatings of houses, bridges and railway cars flexible, so they can withstand different temperature cycles or weather conditions and especially prevent cracking. Silicone coatings are less likely to corrode.
Sporting Apparels and Goods
Silicones are used in goggles and diving masks. Silicones are a lightweight, durable, water repellent and high-performing material. With such properties, silicones can be used to design new sportswear and goods.
Toys
Silicones are used in making different types of toys.
Lubricants
Silicones are used as lubricants in many cases. Silicone greases are used to lubricate airsoft gun parts, bicycle chains and other mechanisms.
Safety and Environmental Considerations
Silicone compounds are pervasive in the environment. While there have been various studies and debates on the safety concerns regarding silicones, many have deemed that this compound is not entering the environment in a quantity or concentration that may cause a danger to human life or health. On the other hand, even though silicone compounds, such as cyclic siloxanes D4 and D5, are air and water pollutants, they have been said to have negative health effects on test animals.
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