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Polydimethylsiloxane (PDMS) is the most widely used silicon-based organic polymer, and is particularly known for it's unusual rheological (or flow) properties. It is optically clear, and is generally considered to be inert, non-toxic and non-flammable. PDMS has been assigned CAS number 63148-62-9, and is occasionally called dimethicone. It is one of several types of silicone oil.The chemical formula for PDMS is
(CH3)3SiO[SiO(CH3)2]nSi(CH3)3, where n is the number of repeating monomer [SiO(CH3)2] units. The polymer is manufactured in multiple viscosities, ranging from a thin pourable liquid (when n is very low), to a thick rubbery semi-solid (when n is very high). PDMS molecules have quite flexible polymer backbones (or chains), which become loosely entangled when molecular weight is high. This results in PDMS having an unusually high level of viscoelasticity.
Viscoelasticity means that at long flow times (or high temperatures), PDMS acts like a viscous liquid, similar to honey. However at short flow times (or low temperatures) it acts like an elastic solidA solid is a state of matter, characterized by a definite volume and a definite shape (i. it resists deformation). Within a solid, atoms/ molecules are relatively close together, or "rigid"; however, this does not prevent the solid from becoming deformed, similar to rubber. In other words, if you leave some PDMS on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface imperfections. However if you roll the same PDMS into a sphere and throw it onto the same surface (short flow time), it will bounce like a rubber ball.
Although the viscoelastic properties of PDMS can be intuitively observed using the simple experiment described above, they can be more accurately measured using dynamic mechanical analysisDynamic mechanical analysis (DMA or dynamic mechanical thermal analysis (DMTA DMA is a technique used to study and characterise materials. It is most especially useful for observing the viscoelastic nature of polymers. An oscillating force is applied to a. This involves using a specialized instrument to determine the material's flow characteristics over a wide range of temperatures, flow rates, and deformations. Because of PDMS's chemical stability, it is often used a calibration fluid for this type of experiment.
Many people are indirectly familiar with PDMS because it is the primary component in Silly PuttySilly Putty is a silicone plastic " clay", marketed as a toy for children by Binney & Smith Inc. It is another one of those scientific accidents on the way to solving another problem: finding a rubber substitute for the United States during World War II., to which PDMS imparts its characteristic viscoelastic properties. PDMS is also used as a component in silicone grease and other silicone based lubricantA lubricant (colloquially, lube is a substance introduced between two moving surfaces to reduce the friction and wear between them. Worldwide, more than 50 million tonnes of lubricants are consumed annually. Automotive engine lubricants comprise approximas, as well as in defoaming agents, damping fluids, heat transferHeat transfer or heat flow is the process whereby heat flows from regions of higher to regions of lower temperature. The flow of heat from one region to another is called a heat current. The rate of heat flow depends on the mode of heat transfer and on th fluids, cosmeticsCosmetics or makeup are substances to enhance the beauty of the human body, apart from simple cleaning. Their use is widespread, especially among women in Western countries (see gender role). In the 1800s, Queen Victoria publicly declared make-up impolite and other applications. PDMS has also been used as a filler fluid in breast implantTopics relating to transitioning A breast implant is a technique used in cosmetic surgery to increase the size of one's breasts or to reconstruct the breast (for example, after a mastectomy). There are three types of breast implants: Saline-filled which hs, although this practice has decreased somewhat, due to safety concerns.
