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POLYDIMETHYLSILOXANE

Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. Polydimethylsiloxane is the most widely used silicon-based organic polymer due to its versatility and properties leading to many applications

CAS : 9016-00-6

Synonyms:
Polydimethylsiloxane ; PDMS; Poly(dimethylsiloxane), dimethylpolysiloxane, dimethylsilicone fluid,; dimethylsilicone oil; dimethicone; INS No. 900a ; 9006-65-9; DIMETHYL POLYSILOXANE; DIMETHYLPOLYSILOXANE; POLY(DIMETHYLSILOXANE); POLYDIMETHYLSILOXANE; OCTAMETHYLTRISILOXANE; Polydimethylsiloksane ; 107-51-7; DIMETHICONE; Trisiloxane, octamethyl-; Dimeticone; Poly(dimethylsiloxane); Dimethicones; Dimethicone 350; 1,1,1,3,3,5,5,5-Octamethyltrisiloxane; Sentry Dimethicone; dimeticonum; Dimeticona; Polysilane; Viscasil 5M; dimethyl-bis(trimethylsilyloxy)silane; UNII-9G1ZW13R0G; Mirasil DM 20; CCRIS 3198; 63148-62-9; Dow Corning 1664; Belsil DM 1000; Dimeticonum [INN-Latin]; EINECS 203-497-4; Dimeticona [INN-Spanish]; Dimethicone 350 [USAN]; 9G1ZW13R0G; CCRIS 3957; CHEBI:9147; HSDB 1808; Trisiloxane,; 1,1,1,3,3,5,5,5-octamethyl-; Dimethylbis(trimethylsilyloxy)silane; Dimethyl polysiloxane, bis(trimethylsilyl)-terminated; MFCD00084411; DC 1664; Dimethyl polysiloxane, dimethyl-terminated; alpha-(Trimethylsilyl)-omega-methylpoly(oxy(dimethylsilylene)); Poly(oxy(dimethylsilylene)), alpha-(trimethylsilyl)-omega-methyl-; MFCD00134211; Ophtasiloxane; Silicone oil; Dimethylbis(trimethylsiloxy)silane; Dimeticone [INN]; Dimethicone 1000; octamethyl-trisiloxane; PDMS; Pentamethyl;(trimethylsilyloxy)disiloxane; dimethicone macromolecule; TYU5GP6XGE; UNII-TYU5GP6XGE; Dimethicone [USAN:NF]; UNII-H8YMB5QY0D; Dimethicone [USAN:BAN];Poly dimethyl siloxane ; Polydimethyl siloxane ; Poly dimethyl siloxan ; Polydimethyl siloxan ; Polidimetilsiloksan; Polydimetilsiloksan; Polidimetil siloksan; Poli dimetil siloksan

Polydimethylsiloxane

Polydimethylsiloxane
PDMS
PDMS
Names
IUPAC name
poly(dimethylsiloxane)
Other names
PDMS
dimethicone
dimethylpolysiloxane
E900
Identifiers
CAS Number
63148-62-9 ☒
3D model (JSmol)
n = 12: Interactive image
ChemSpider
none
ECHA InfoCard   100.126.442
E number   E900 (glazing agents, ...)
UNII
92RU3N3Y1O check
CompTox Dashboard (EPA)
DTXSID0049573
Properties
Chemical formula   (C2H6OSi)n
Density   965 kg/m3
Melting point   N/A (vitrifies)
Boiling point   N/A (vitrifies)
Pharmacology
ATC code   P03AX05 (WHO)
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
110
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒ verify (what is check☒ ?)
Infobox references
Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones.[1] Polydimethylsiloxane is the most widely used silicon-based organic polymer due to its versatility and properties leading to many applications.[2]

It is particularly known for its unusual rheological (or flow) properties. Polydimethylsiloxane is optically clear and, in general, inert, non-toxic, and non-flammable. It is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos (as it makes hair shiny and slippery), food (antifoaming agent), caulking, lubricants and heat-resistant tiles.

Structure
The chemical formula for Polydimethylsiloxane is CH3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [SiO(CH3)2] units.[3] Industrial synthesis can begin from dimethyldichlorosilane and water by the following net reaction:

The polymerization reaction evolves hydrochloric acid. For medical and domestic applications, a process was developed in which the chlorine atoms in the silane precursor were replaced with acetate groups. In this case, the polymerization produces acetic acid, which is less chemically aggressive than HCl. As a side-effect, the curing process is also much slower in this case. The acetate is used in consumer applications, such as silicone caulk and adhesives.

Branching and capping
Hydrolysis of Si(CH3)2Cl2 generates a polymer that is terminated with silanol groups (−Si(CH3)2OH]). These reactive centers are typically "capped" by reaction with trimethylsilyl chloride:

2 Si(CH3)3Cl + [Si(CH3)2O]n−2[Si(CH3)2OH]2 → [Si(CH3)2O]n−2[Si(CH3)2O Si(CH3)3]2 + 2 HCl
Silane precursors with more acid-forming groups and fewer methyl groups, such as methyltrichlorosilane, can be used to introduce branches or cross-links in the polymer chain. Under ideal conditions, each molecule of such a compound becomes a branch point. This can be used to produce hard silicone resins. In a similar manner, precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain.

Well-defined Polydimethylsiloxane with a low polydispersity index and high homogeneity is produced by controlled anionic ring-opening polymerization of hexamethylcyclotrisiloxane. Using this methodology it is possible to synthesize linear block copolymers, heteroarm star-shaped block copolymers and many other macromolecular architectures.

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). Polydimethylsiloxane molecules have quite flexible polymer backbones (or chains) due to their siloxane linkages, which are analogous to the ether linkages used to impart rubberiness to polyurethanes. Such flexible chains become loosely entangled when molecular weight is high, which results in PDMS' unusually high level of viscoelasticity.

Mechanical properties
Polydimethylsiloxane is viscoelastic, meaning that at long flow times (or high temperatures), it acts like a viscous liquid, similar to honey. However, at short flow times (or low temperatures), it acts like an elastic solid, similar to rubber. Viscoelasticity is a form of nonlinear elasticity that is common amongst noncrystalline polymers.[4] The loading and unloading of a stress-strain curve for Polydimethylsiloxane do not coincide; rather, the amount of stress will vary based on the degree of strain, and the general rule is that increasing strain will result in greater stiffness. When the load itself is removed, the strain is slowly recovered (rather than instantaneously). This time-dependent elastic deformation results from the long-chains of the polymer. But the process that is described above is only relevant when cross-linking is present; when it is not, the polymer Polydimethylsiloxane cannot shift back to the original state even when the load is removed, resulting in a permanent deformation. However, permanent deformation is rarely seen in PDMS, since it is almost always cured with a cross-linking agent.

If some Polydimethylsiloxane is left on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface imperfections. However, if the same Polydimethylsiloxane is poured into a spherical mold and allowed to cure (short flow time), it will bounce like a rubber ball.[3] The mechanical properties of Polydimethylsiloxane enable this polymer to conform to a diverse variety of surfaces. Since these properties are affected by a variety of factors, this unique polymer is relatively easy to tune. This enables Polydimethylsiloxane to become a good substrate that can easily be integrated into a variety of microfluidic and microelectromechanical systems.[5][6] Specifically, the determination of mechanical properties can be decided before Polydimethylsiloxane is cured; the uncured version allows the user to capitalize on myriad opportunities for achieving a desirable elastomer. Generally, the cross-linked cured version of Polydimethylsiloxane resembles rubber in a solidified form. It is widely known to be easily stretched, bent, compressed in all directions.[7] Depending on the application and field, the user is able to tune the properties based on what is demanded.

Fabric embedded within PDMS. This technique enables a user to retain a thin layer of Polydimethylsiloxane as a substrate while achieving a higher stiffness through the insertion of reinforcement.

Linear relationship in Sylgard 184 Polydimethylsiloxane between curing temperature and Young's modulus
Overall Polydimethylsiloxane has a low elastic modulus which enables it to be easily deformed and results in the behavior of a rubber.[8][9][10] Viscoelastic properties of Polydimethylsiloxane can be more precisely measured using dynamic mechanical analysis. This method requires determination of 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 as a calibration fluid for this type of experiment.

The shear modulus of Polydimethylsiloxane varies with preparation conditions, and consequently dramatically varies in the range of 100 kPa to 3 MPa. The loss tangent is very low (tan δ ≪ 0.001).[10]

Chemical compatibility
Polydimethylsiloxane is hydrophobic.[6] Plasma oxidation can be used to alter the surface chemistry, adding silanol (SiOH) groups to the surface. Atmospheric air plasma and argon plasma will work for this application. This treatment renders the Polydimethylsiloxane surface hydrophilic, allowing water to wet it. The oxidized surface can be further functionalized by reaction with trichlorosilanes. After a certain amount of time, recovery of the surface's hydrophobicity is inevitable, regardless of whether the surrounding medium is vacuum, air, or water; the oxidized surface is stable in air for about 30 minutes.[11] Alternatively, for applications where long-term hydrophilicity is a requirement, techniques such as hydrophilic polymer grafting, surface nanostructuring, and dynamic surface modification with embedded surfactants can be of use. [12]

Solid Polydimethylsiloxane samples (whether surface-oxidized or not) will not allow aqueous solvents to infiltrate and swell the material. Thus Polydimethylsiloxane structures can be used in combination with water and alcohol solvents without material deformation. However most organic solvents will diffuse into the material and cause it to swell.[6] Despite this, some organic solvents lead to sufficiently small swelling that they can be used with PDMS, for instance within the channels of Polydimethylsiloxane microfluidic devices. The swelling ratio is roughly inversely related to the solubility parameter of the solvent. Diisopropylamine swells Polydimethylsiloxane to the greatest extent; solvents such as chloroform, ether, and THF swell the material to a large extent. Solvents such as acetone, 1-propanol, and pyridine swell the material to a small extent. Alcohols and polar solvents such as methanol, glycerol and water do not swell the material appreciably.[13]

Applications
Surfactants and antifoaming agents
Polydimethylsiloxane is a common surfactant and is a component of defoamers.[14] PDMS, in a modified form, is used as an herbicide penetrant[15] and is a critical ingredient in water-repelling coatings, such as Rain-X.[16]

Hydraulic fluids and related applications
Dimethicone is also the active silicone fluid in automotive viscous limited slip differentials and couplings. This is usually a non-serviceable OEM component but can be replaced with mixed performance results due to variances in effectiveness caused by refill weights or non-standard pressurizations.[citation needed]

Soft lithography
Polydimethylsiloxane is commonly used as a stamp resin in the procedure of soft lithography, making it one of the most common materials used for flow delivery in microfluidics chips.[17] The process of soft lithography consists of creating an elastic stamp, which enables the transfer of patterns of only a few nanometers in size onto glass, silicon or polymer surfaces. With this type of technique, it is possible to produce devices that can be used in the areas of optic telecommunications or biomedical research. The stamp is produced from the normal techniques of photolithography or electron-beam lithography. The resolution depends on the mask used and can reach 6 nm.[18]

In biomedical (or biological) microelectromechanical systems (bio-MEMS), soft lithography is used extensively for microfluidics in both organic and inorganic contexts. Silicon wafers are used to design channels, and Polydimethylsiloxane is then poured over these wafers and left to harden. When removed, even the smallest of details is left imprinted in the PDMS. With this particular Polydimethylsiloxane block, hydrophilic surface modification is conducted using plasma etching techniques. Plasma treatment disrupts surface silicon-oxygen bonds, and a plasma-treated glass slide is usually placed on the activated side of the Polydimethylsiloxane (the plasma-treated, now hydrophilic side with imprints). Once activation wears off and bonds begin to reform, silicon-oxygen bonds are formed between the surface atoms of the glass and the surface atoms of the PDMS, and the slide becomes permanently sealed to the PDMS, thus creating a waterproof channel. With these devices, researchers can utilize various surface chemistry techniques for different functions creating unique lab-on-a-chip devices for rapid parallel testing.[5] Polydimethylsiloxane can be cross-linked into networks and is a commonly used system for studying the elasticity of polymer networks.[citation needed] Polydimethylsiloxane can be directly patterned by surface-charge lithography.[19]

Polydimethylsiloxane is being used in the making of synthetic gecko adhesion dry adhesive materials, to date only in laboratory test quantities.[20]

Some flexible electronics researchers use Polydimethylsiloxane because of its low cost, easy fabrication, flexibility, and optical transparency.[21]

Stereo lithography
In stereo lithography (SLA) 3D printing, light is projected onto photocuring resin to selectively cure it. Some types of SLA printer are cured from the bottom of the tank of resin and therefore require the growing model to be peeled away from the base in order for each printed layer to be supplied with a fresh film of uncured resin. A Polydimethylsiloxane layer at the bottom of the tank assists this process by absorbing oxygen : the presence of oxygen adjacent to the resin prevents it adhering to the PDMS, and the optically clear Polydimethylsiloxane permits the projected image to pass through to the resin undistorted.

Medicine and cosmetics
Activated dimethicone, a mixture of Polydimethylsiloxane s and silicon dioxide (sometimes called simethicone), is often used in over-the-counter drugs as an antifoaming agent and carminative.[22][23] It has also been at least proposed for use in contact lenses.[24]

Silicone breast implants are made out of a Polydimethylsiloxane elastomer shell, to which fumed amorphous silica is added, encasing Polydimethylsiloxane gel or saline solution. [25]

In addition, Polydimethylsiloxane is useful as a lice or flea treatment because of its ability to trap insects.[26] It also works as a moisturizer that is lighter and more breathable than typical oils.

Skin
Polydimethylsiloxane is used variously in the cosmetic and consumer product industry as well. For example, Polydimethylsiloxane can be used in the treatment of head lice on the scalp[26] and dimethicone is used widely in skin-moisturizing lotions where it is listed as an active ingredient whose purpose is "skin protection." Some cosmetic formulations use dimethicone and related siloxane polymers in concentrations of use up to 15%. The Cosmetic Ingredient Review's (CIR) Expert Panel, has concluded that dimethicone and related polymers are "safe as used in cosmetic formulations."[27]

Hair
Polydimethylsiloxane compounds such as amodimethicone, are effective conditioners when formulated to consist of small particles and be soluble in water or alcohol/act as surfactants[28][29] (especially for damaged hair[30]), and are even more conditioning to the hair than common dimethicone and/or dimethicone copolyols.[31]

Contact Lenses
A proposed use of Polydimethylsiloxane is contact lens cleaning. Its physical properties of low elastic modulus and hydrophobicity have been used to clean micro and nano pollutants from contact lens surfaces more effectively than multipurpose solution and finger rubbing; the researchers involved call the technique PoPPR (polymer on polymer pollution removal) and note that it is highly effective at removing nanoplastic that has adhered to lenses.[32]

Flea treatment for pets
Dimethicone is the active ingredient in a liquid applied to the back of the neck of a cat or dog from a small one time use dose disposable pipette. The parasite becomes trapped and immoblised in the substance and thus breaks the life cycle of the insect.

Foods
Polydimethylsiloxane is added to many cooking oils (as an antifoaming agent) to prevent oil splatter during the cooking process. As a result of this, Polydimethylsiloxane can be found in trace quantities in many fast food items such as McDonald's Chicken McNuggets, french fries, hash browns, milkshakes and smoothies[33] and Wendy's french fries.[34]

Under European food additive regulations, it is listed as E900.

Condom lubricant
Polydimethylsiloxane is widely used as a condom lubricant.[35][36]

Domestic and niche uses
Many people are indirectly familiar with Polydimethylsiloxane because it is an important component in Silly Putty, to which Polydimethylsiloxane imparts its characteristic viscoelastic properties.[37] Another toy Polydimethylsiloxane is used in is Kinetic Sand. The rubbery, vinegary-smelling silicone caulks, adhesives, and aquarium sealants are also well-known. Polydimethylsiloxane is also used as a component in silicone grease and other silicone based lubricants, as well as in defoaming agents, mold release agents, damping fluids, heat transfer fluids, polishes, cosmetics, hair conditioners and other applications. Polydimethylsiloxane has also been used as a filler fluid in breast implants.

It can be used as a sorbent for the analysis of headspace (dissolved gas analysis) of food.[38]

Safety and environmental considerations
According to Ullmann's Encyclopedia, no "marked harmful effects on organisms in the environment" have been noted for siloxanes. Polydimethylsiloxane is nonbiodegradable, but is absorbed in waste water treatment facilities. Its degradation is catalyzed by various clays.

Polydimethylsiloxane
Polydimethylsiloxane (PDMS) is one of the high-performance polymers, with unique physical and chemical properties like flexible, thermo-tolerant, resistant to oxidation, ease of fabrication, tunable hardness, and other desirable properties.

Polydimethylsiloxane (PDMS) is the simplest member of the silicone polymer family. It is formed by hydrolyzing Me2SiCl2, which is produced from high-purity SiO2 and CH2Cl2 by the Muller–Rochow reaction. The term “silicone” was coined by chemist F. S. Kipping in 1901.

Low–molecular weight Polydimethylsiloxane is a liquid used in lubricants, antifoaming agents, and hydraulic fluids. Its use in breast implants is not as popular as it once was because of safety concerns.

At higher molecular weights, Polydimethylsiloxane is a soft, compliant rubber or resin. It is used in caulks, sealants, an even Silly Putty. More recently, Polydimethylsiloxane resins have been used in soft lithography, a key process in biomedical microelectromechanical systems (bio-MEMS).

Polydimethylsiloxane

Polydimethylsiloxane
IUPAC name   poly(dimethylsiloxane)
Other names   PDMS
dimethicone
E900
Identifiers
CAS number   63148-62-9
Properties
Molecular formula   (C2H6OSi)n
Density   965 kg m−3
Melting point
N/A (vitrifies)

Boiling point
below about 200 °C

Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references
Polydimethylsiloxane (PDMS) is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. Its applications range from contact lenses and medical devices to elastomers, caulking, lubricating oils and heat resistant tiles.

Polydimethylsiloxane is optically clear, and is generally considered to be inert, non-toxic and non-flammable. It has been assigned CAS number 63148-62-9, and is occasionally called dimethicone. It is one of several types of silicone oil (polymerized siloxane).

Chemistry
The chemical formula for Polydimethylsiloxane is (H3C)3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [SiO(CH3)2] units. Industrial synthesis can begin from dimethylchlorosilane and water by the following net reaction:

n [Si(CH3)2Cl2] + n [H2O] → [Si(CH3)2O]n + 2n HCl
During polymerization, this reaction evolves potentially hazardous hydrogen chloride gas. For medical uses, a process was developed where the chlorine atoms in the silane precursor were replaced with acetate groups, so that the reaction product of the final curing process is nontoxic acetic acid (vinegar). As a side effect, the curing process is also much slower in this case. This is the chemistry used in consumer applications, such as silicone caulk and adhesives.

Silane precursors with more acid-forming groups and fewer methyl groups, such as methyltrichlorosilane, can be used to introduce branches or cross-links in the polymer chain. Ideally, each molecule of such a compound becomes a branch point. This can be used to produce hard silicone resins. Similarly, precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain.

Mechanical properties
Polydimethylsiloxane is viscoelastic, meaning that at long flow times (or high temperatures), it acts like a viscous liquid, similar to honey. However at short flow times (or low temperatures) it acts like an elastic solid, similar to rubber. In other words, if you leave some Polydimethylsiloxane 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 Polydimethylsiloxane 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 Polydimethylsiloxane can be intuitively observed using the simple experiment described above, they can be more accurately measured using dynamic mechanical analysis. 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 as a calibration fluid for this type of experiment.

The shear modulus of Polydimethylsiloxane varies with preparation conditions, but is typically in the range of 100 kPa to 3 MPa. The loss tangent is very low (tandeltall0.001).[1]

Chemical compatibility
After polymerization and cross-linking, solid Polydimethylsiloxane samples will present an external hydrophobic surface.[2] This surface chemistry makes it difficult for polar solvents (such as water) to wet the Polydimethylsiloxane surface, and may lead to adsorption of hydrophobic contaminants. Plasma oxidation can be used to alter the surface chemistry, adding silanol (SiOH) groups to the surface. This treatment renders the Polydimethylsiloxane surface hydrophilic, allowing water to wet (this is frequently required for, e.g. water-based microfluidics). The oxidized surface resists adsorption of hydrophobic and negatively charged species. The oxidized surface can be further functionalized by reaction with trichlorosilanes. Oxidized surfaces are stable for ~30 minutes in air, after a certain time hydrophobic recovery of the surface is inevitable independently of the surrounding medium whether it is vacuum, air or water.[3]

Solid Polydimethylsiloxane samples (whether surface oxidized or not) will not allow aqueous solvents to infiltrate and swell the material. Thus Polydimethylsiloxane structures can be used in combination with water and alcohol solvents without material deformation. However most organic solvents will diffuse into the material and cause it to swell,[2] making them incompatible with Polydimethylsiloxane devices. Despite this, some organic solvents lead to sufficiently small swelling that they can be used with Polydimethylsiloxane, for instance within the channels of Polydimethylsiloxane microfluidic devices. The swelling ratio is roughly inversely related to the solubility parameter of the solvent. Diisopropylamine swells Polydimethylsiloxane to the greatest extent, solvents such as chloroform, ether, and THF swell the material to a large extent. Solvents such as acetone, 1-propanol, and pyridine swell the material to a small extent. Alcohols and polar solvents such as methanol, glycerol and water do not swell the material appreciably.[4]

Applications
Many people are indirectly familiar with Polydimethylsiloxane because it is an important (4%) component in Silly Putty, to which Polydimethylsiloxane imparts its characteristic viscoelastic properties. The rubbery, vinegary-smelling silicone caulks, adhesives, and aquarium sealants are also well-known. Polydimethylsiloxane is also used as a component in silicone grease and other silicone based lubricants, as well as in defoaming agents, mold release agents, damping fluids, heat transfer fluids, polishes, cosmetics, hair conditioners and other applications. Polydimethylsiloxane has also been used as a filler fluid in breast implants, although this practice has decreased somewhat, due to safety concerns. It continues to be used in knuckle replacement implants, with good results.

Activated dimethicone, a mixture of Polydimethylsiloxane s and silicon dioxide (sometimes called simethicone), is used in Over-the-counter drug as an anti-foaming agent and carminative.

As a food additive, it has the E number E900 and is used as an anti-foaming agent and an anti-caking agent.

Polydimethylsiloxane is commonly used as a stamp resin in the procedure of soft lithography, making it one of the most common materials used for flow delivery in microfluidics chips.

Polydimethylsiloxane can be cross-linked into networks and is a commonly used system for studying the elasticity of polymer networks.

Polydimethylsiloxane can be used in the treatment of head lice.

Dimethicone is also used widely in skin moisturizing lotions, listed as an active ingredient whose purpose is "skin protectant." Some cosmetic formulations use dimethicone and related siloxane polymers in concentrations of use up to 15%. The Cosmetic Ingredient Review's (CIR) Expert Panel, has concluded that dimethicone and related polymers are "safe as used in cosmetic formulations" [1]

Polydimethylsiloxane is also used in analytical chemistry as a component of some types of SPME fibers.

Introduction
Polydimethylsiloxane (PDMS) is a commonly used silicon-based organic polymer. Due to its unique mechanical, chemical, and optical properties, it has become integrated into many optical and micro-fluidic devices.

Polydimethylsiloxane can be purchased as a two-part kit. The kit consists of a base and a cross-linking agent. The two parts are in a viscous liquid form until mixed and cross-linking occurs. The cross-linking procedure will occur without other aid once the two parts are mixed. However, the procedure can be greatly accelerated with heat. The mixing ratios and curing procedures used during development determine the mechanical, chemical, and optical properties of the final solid.

2. Polydimethylsiloxane Mechanical Properties
When cross-linked, Polydimethylsiloxane acts like a rubbery solid. In this state, the polymer does not permanently deform when under stress or strain. Rather, the elastic polymer will return to its original shape when released. The elastic properties of Polydimethylsiloxane are highly dependent on the amount of cross-linking agent (often is used methyltrichlorosilane) integrated into the polymer. The higher the concentration of the cross-linking agent, the more solid the final polymer becomes. With little or no cross-linking agent, the polymer will remain a viscous liquid. Since the curing process changes Polydimethylsiloxane from a liquid into an elastic solid, Polydimethylsiloxane is commonly used in micro-fabrication molds. Polydimethylsiloxane has been also used as walls for micro-fluidic channels and as a silicon wafer bonding agent. [1]

3. Polydimethylsiloxane Chemical Properties
Polydimethylsiloxane is generally considered to be chemically inert and also notably hydrophobic, meaning that water cannot easily penetrate its surface. This property has led extended use of Polydimethylsiloxane in micro-fluidics. However, most organic solvents can still penetrate the Polydimethylsiloxane surface, limiting its versatility. Polydimethylsiloxane has also increasingly been used in extraction processes, where Polydimethylsiloxane is used to remove organic contaminants from water for analysis. As organic solvents are absorbed into the polymer, the volume of the polymer must increase, or swell, referred to the volume of the introduced chemicals. The solubility parameter of each chemical determines the amount of swelling that occurs. Neither chemical absorption, nor physical swelling are permanent. The absorbed chemicals can just as easily diffuse out of the polymer as they can diffuse in. The diffusion mechanics are dependent on equilibrium states between the polymer and the surrounding medium. Therefore, absorbed chemicals will remain in the polymer as long as a similar concentration of that chemical exists in the surrounding medium at the Polydimethylsiloxane surface. If the concentration in the medium decreases, then diffusion mechanics will cause the absorbed chemical to naturally flow out of the Polydimethylsiloxane until a new equilibrium is met.

4. Polydimethylsiloxane Optical Properties
Polydimethylsiloxane is optically clear at a wide range of wavelengths. In addition, the curing time and temperature used during cross-linking can determine the refractive index (RI) of the bulk. Since the polymer can be easily molded, it has been used to form lenses and waveguides. Also, the effective refractive index and the absorption spectrum of Polydimethylsiloxane are changed when organic compounds are physically absorbed into the polymer. These properties have created the basis for several fiber-optic based chemical sensors. Through monitoring changes in refractive index or absorption spectrum, chemical concentrations absorbed into a volume of Polydimethylsiloxane may be identified and characterized.

Polydimethylsiloxane (PDMS) fluids are available in a broad range of viscosities and are used in a wide range of applications. Polydimethylsiloxane fluids are known in the beauty and personal care industry by their INCI name, i.e.“dimethicone.” The Dow Corning commercial name of Polydimethylsiloxane is XIAMETER®.[ 2 ]

Very-low-viscosity (≤ 2 cSt) Polydimethylsiloxane fluids are categorized as volatile methylsiloxanes (VMS). In the United States, VMS fluids are exempt from regulation as volatile organic compounds (VOCs).

Features And Benefits of PDMS

Excellent water repellency
Good dielectric properties over a wide range of temperatures and frequencies.
Low glass transition (Tg) temperature
Low surface tension
Heat stability
Oxidation resistance
Very low vapor pressure
High flash point
Inert, nonreactive
Typical Uses

Mechanical fluids
Dielectric coolants
Insulating and damping fluids for electrical and electronic equipment
Release agents
Foam control
Surface active fluids
Lubricants
Ingredients for cosmetic and personal care formulations, polishes and specialty chemical products
Plastics additives
Most Polydimethylsiloxane s are non-volatile organosilicon polymers consisting of
(CH3)2 SiO structural units as shown below :

Polydimethylsiloxane s

Polydimethylsiloxane structure, where typically x > 4

Various Polydimethylsiloxane fluids are linear, ranging in viscosity from very low to ultrahigh viscosities.

Polydimethylsiloxane fluids draw strength, stability and flexibility from their siloxane backbone.
Polydimethylsiloxane fluids gain inertness, lubricity, release properties and water repellency from their attached methyl groups,.
Consequently, they are used in a wide range of industrial applications, such as paper, leather goods or textiles. They often serve as antifoams, softeners or water repellents. [3]

Polydimethylsiloxane fluids can also be found in auto motive care products, personal – and household products.

5. Environment and Recycling
Due to their wide range of applications, Polydimethylsiloxane fluids can enter the environment in different ways. Since they are non-volatile, Polydimethylsiloxane do not evaporate into the atmosphere. In household products, only very small quantities of Polydimethylsiloxane fluids can be washed from the surfaces to which they have been applied , eventually into the soil or a water treatment plant. This is the case for personal care products such as conditioners and shampoos, that are rinsed away after use and consequently the Polydimethylsiloxane they contain is carried with water to the treatment site. In industrial applications, where Polydimethylsiloxane are used as surface treatments or process aids, small quantities may be found in process water too. About 17% of the total Polydimethylsiloxane production volume worldwide is used in “ down – the – drain” applications.

End-use industrial products such as transformer fluids are used in contained applications. These are suitable for recycling and unlikely to enter the environment, except in cases of accidental release.

A number of studies have shown that Polydimethylsiloxane will degrade into compounds of lower molecular weight when in contact with soils, especially into (CH3)2Si(OH)2 [4]. The phenomenon is widespread in nature, as confirmed by testing under different representative conditions in a wide range of soils. A significant degradation to lower molecular weights was observed after only few weeks of soil contact. The degradation rate and extent vary as a function of soil moisture content and of clay type. It was shown that the resulting degradation products further oxidize in the environment, both biologically and abiotically , in order to form silica, carbon dioxide and water.

It was not observed any effect from Polydimethylsiloxane or its degradation products on plant growth, seed germination or the plant biomass [5]

Polydimethylsiloxane fluids are not classified as hazardous materials. Specific testing has shown that Polydimethylsiloxane is not toxic and does not bioaccumulate in sediment-dwelling organisms. Consequently, Polydimethylsiloxane is not relevant for European product labeling.

Water treatment plants and on-site septic systems are both designed to facilitate the natural degradation of this water by microscopic organisms. Biomass ( sludge ) is generated by this degradation and must eventually be discarded. The treated sludge in a municipal system is typically landfilled, incinerated or used as a fertilizer . In on-site septic systems, common in US, the tank is periodically pumped out and the biomass is taken to the water treatment plant.

Usually Polydimethylsiloxane fluids resulted from personal care and household products enter into the mentioned treatment systems as tiny dispersed droplets in water. Due to the fact that the Polydimethylsiloxane fluids are essentially not soluble in water, they attach to the suspended materials in water systems and therefore become a minor part of the sludge.

Polydimethylsiloxane does not inhibit the microbial activity by which water is treated. Also, Polydimethylsiloxane loadings had no effect on the operating parameters (such as pH, suspended solids, specific oxygen uptake) or physiological activity of the micro-flora in the activated sludge units. Sludge digestion operating parameters were also unaffected by loadings of up to 100 mg/kg of Polydimethylsiloxane [6].

The ultimate fate of sludge-bound Polydimethylsiloxane depends on the sludge disposal technique. If the sludge is incinerated, the silicone converts to amorphous silica, which has no further environmental consequence when the ash is landfilled. When treated sludge is used as fertilizer, very small percents of Polydimethylsiloxane may be introduced to the soil environment, where it is subject to soil-catalyzed degradation. Consequently, Polydimethylsiloxane had shown no significant environmental effects.