Polydimethylsiloxane, also known as dimethylpolysiloxane or dimethicone, is a silicone polymer with a wide variety of uses, from cosmetics to industrial lubrication.
Polydimethylsiloxane is particularly known for its unusual rheological (or flow) properties.
CAS Number: 9006-65-9
E number: E900 (glazing agents, ...)
Chemical formula: CH3[Si(CH3)2O]nSi(CH3)3
Polydimethylsiloxane is the simplest member of the silicone polymer family.
Polydimethylsiloxane 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.
At higher molecular weights, Polydimethylsiloxane is a soft, compliant rubber or resin.
Polydimethylsiloxane is a silicone elastomer most often used in microfluidic or lab-on-a-chip applications to form devices with defined microstructures.
Polydimethylsiloxane is optically clear, and is generally considered to be inert, non-toxic and non-flammable.
Polydimethylsiloxane is one of several types of silicone oil (polymerized siloxane).
Polydimethylsiloxane is a colorless and transparent new polymer materials, a variety of different viscosities (5cps ~ 2million cps), the liquid from flowing easily into a thick semi-solid material.
Polydimethylsiloxane has a special smoothness, softness, hydrophobicity, good chemical stability, excellent electrical insulation and resistance to high temperature.
Polydimethylsiloxane has been assigned CAS number 63148-62-9, and is occasionally called dimethicone.
Polydimethylsiloxane has high flash point, low freezing point, long-term using between -50 ℃ ~ +200 ℃, low viscosity-temperature coefficient, high compression ratio, low surface tension,water-repellent moisture resistance, low heat conduction coefficient.
Polydimethylsiloxane consists of fully methylated linear siloxane polymers containing repeating units of the formula [(CH3)2SiO] with trimethylsiloxy end-blocking units of the formula (CH3)3SiO-.
The additive is produced by hydrolysis of a mixture of dimethyldichlorosilane and a small quantity of trimethylchlorosilane.
The average molecular weights of the linear polymers range from
approximately 6,800 to 30,000.
Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are referred to as silicones and is the most widely used silicon-based organic-polymer.
Polydimethylsiloxane (PDMS) is particularly known for its unusual rheological or flow properties.
Polydimethylsiloxane is optically clear and inert, non-toxic, and non-flammable.
Polydimethylsiloxane is one of several types of silicone oil (polymerized siloxane).
Polydimethylsiloxane is a non-conducting, silicone-based elastomer that is of widespread interest due to its flexibility and ease of micromolding for the rapid prototyping of microdevices and systems.
Also examined are the properties which make polydimethylsiloxane an excellent candidate for understanding complex biological behaviors, including its transparency for applying optical methods, biocompatibility and nontoxicity, high conformity with cells and other biostructures, gas permeability for the transfer of nutrients and oxygen, and flexibility.
In the subsequent study, a hybrid material of titanium dioxide and polydimethylsiloxane is obtained and characterized using a sol-gel and electrospraying method.
These results indicate that the hybrid material may be viable as an adsorbent, and that the optimization of the process could reduce both cost and analysis time.
In order to further the applications of polydimethylsiloxane, the closing study describes the steps in the fabrication of its plasmonic structure, and also examines the switching effect of the sample.
Polydimethylsiloxane, also known as dimethylpolysiloxane or dimethicone, is a silicone polymer with a wide variety of uses, from cosmetics to industrial lubrication.
Polydimethylsiloxane is particularly known for its unusual rheological (or flow) properties.
Polydimethylsiloxane is optically clear and, in general, inert, non-toxic, and non-flammable.
Polydimethylsiloxane is one of several types of silicone oil (polymerized siloxane).
Polydimethylsiloxane's 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), caulk, lubricants and heat-resistant tiles.
Polydimethylsiloxane emulsion is the most widely used silicon-based organic polymer and is particularly known for its unusual rheological (or flow) properties.
Polydimethylsiloxane, called PDMS or dimethicone, is a polymer widely used for the fabrication and prototyping of microfluidic chips.
Polydimethylsiloxane is a mineral-organic polymer (a structure containing carbon and silicon) of the siloxane family (word derived from silicon, oxygen and alkane).
For the fabrication of microfluidic devices, Polydimethylsiloxane (liquid) mixed with a cross-linking agent is poured into a microstructured mold and heated to obtain a elastomeric replica of the mold (cross-linked).
All silicones are characterised by the repeating siloxane unit which consists of one Si-O group each.
A wide range of side groups can be bound to the silicon atom.
With Polydimethylsiloxane, they are methyl groups CH3.
Various chain ends can be coupled to the polymer.
Often, this is the trimethylsiloxyl group Si-SH3.
The shortest molecule consisting only of the two end groups without dimethysiloxane monomer units is hexamethyl disiloxane HMDSO; it is very important as a process gas for hydrophobic plasma coating.
Polydimethylsiloxane is a linear polymers which are liquid up to very high molecular weights.
But they can be crosslinked, which gives them elastomeric properties.
USES and APPLICATIONS of POLYDIMETHYLSILOXANE:
Hydraulic fluids and related applications: Polydimethylsiloxane is used in the active silicone fluid in automotive viscous limited slip differentials and couplings.
Many people are indirectly familiar with Polydimethylsiloxane because it is an important (4%) component in Silly Putty, to which PDMS 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.
Polydimethylsiloxane continues to be used in knuckle replacement implants, with good results.
Activated dimethicone, a mixture of polydimethylsiloxanes and silicon dioxide (sometimes called simethicone), is used in Over-the-counter drug as an anti-foaming agent and carminative.
As a food additive, Polydimethylsiloxane 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.
Polydimethylsiloxane 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.
Polydimethylsiloxane is also used in analytical chemistry as a component of some types of SPME fibers.
Polydimethylsiloxane is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties.
Polydimethylsiloxane's applications range from contact lenses and medical devices to elastomers, caulking, lubricating oils and heat resistant tiles.
Polydimethylsiloxane 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).
Condom lubricant: Polydimethylsiloxane is widely used as a condom lubricant.
Polydimethylsiloxane is used Component of defoamers, Ingredient in water-repellent coatings, Plasticizer in silicone sealants, Stamp resin in the procedure of soft-lithography, Lubricant in condoms, A component in silicone grease, A component in heat-transfer fluids, A component in mold-release agents, and
Sorbent for the analysis of head-space.
In addition to applications in microfluidics, Polydimethylsiloxane has been widely used in the fabrication of biomodels (flow phantom) for the in vitro hemodynamic study of diseases such as aneurysms and stenosis.
The biomodels developed in Polydimethylsiloxane allow good replicability of the lumen of the arteries and good transparency, being ideal for the application of optical techniques of micro particle image velocimetry (micro-PIV), particle image velocimetry (PIV), particle tracking velocimetry (PTV) and non-evasive techniques.
These experimental tests have provided a greater understanding of these pathologies, validated numerical techniques, and tested medical devices such as stents.
Polydimethylsiloxane has also been investigated in the field of medical implants.
Polydimethylsiloxane, or PDMS for short, is a polymer of the silicones type; it is used very often and for many different purposes.
These types of implants are usually made with titanium or Polydimethylsiloxane alloys; however, such materials do not allow good osseointegration.
In order to overcome this limitation, Polydimethylsiloxane has been studied to produce coatings with microscale features that help the bonding between the implant and the bone.
The main characteristics for its use in implants are its high biocompatibility, excellent resistance to biodegradation and flexibility, which makes Polydimethylsiloxane one of the most successful polymers in implanted devices, presenting only mild foreign body reactions.
Common applications of Polydimethylsiloxane include cardiac pacemakers, cuff and book electrodes in the PNS, cochlear implants, bladder and pain controllers and planar electrode arrays in the CNS.
Further, Polydimethylsiloxane is used in contact lenses, medical devices to elastomers and in shampoos (as dimethicone makes hair shiny and slippery).
Polydimethylsiloxane finds application as an antifoaming agent in food, caulking, lubricants, kinetic sand and heat-resistant tiles.
In addition to this, Polydimethylsiloxane serves as a critical ingredient in water-repelling coatings such as Rain-X.
Polydimethylsiloxane is an elastomer with excellent optical, electrical and mechanical properties, which makes it well-suited for several engineering applications.
Due to its biocompatibility, Polydimethylsiloxane is widely used for biomedical purposes.
Polydimethylsiloxane is an elastomeric polymer with interesting properties for biomedical applications, including physiological indifference, excellent resistance to biodegradation, biocompatibility, chemical stability, gas permeability, good mechanical properties, excellent optical transparency and simple fabrication by replica moulding.
Some properties of Polydimethylsiloxane can be improved by adding additives.
Due to these characteristics, Polydimethylsiloxane has been widely used in micropumps, catheter surfaces, dressings and bandages, microvalves, optical systems, in the in vitro study of diseases, in implants, in microfluidics and photonics.
Soft-lithography techniques such as micro-contact printing, replica moulding, micro-transfer moulding, micro-moulding in capillaries and solvent-assisted micro-moulding usually require the use of Polydimethylsiloxane to create an elastomeric stamp or mould that incorporates nano- and microstructures for the transfer of patterns onto a subsequent substrate.
Apart from microfluidics, Polydimethylsiloxane is used as a food additive (E900), in shampoos, and as an anti-foaming agent in beverages or in lubricating oils.
Polydimethylsiloxane is used release agent, lubricant, antifoam agent, liquid dielectric for electrical and electronic equipment, polish additive, additive for textile and fiber auxiliaries, chemical auxiliary material, glass vial and lens coating, penetrating oil ingredient, and surface active agent.
Polydimethylsiloxane is an almost inert polymer which is highly resistant to oxidation, but it can also be used as an electric insulator in organic electronics (micro-electronics or polymer electronics) or in biological micro-analytics.
One of the most frequent applications of low-pressure plasma with Polydimethylsiloxane is in the field of micro-fluidic systems; here, a certain polydimethysiloxane (such as Sylgard 184) is structured by the customer to match the respective application.
Next, a plasma treatment is carried out and the Polydimethylsiloxane chip can be irreversibly attached to a glass plate, a silicon surface or another substrate.
Moreover, soft-lithography technology has driven the use of Polydimethylsiloxane in microelectromechanical systems (MEMS) applications and in microfluidic components.
-MEMS are approaches that use electronic and mechanical technologies to deal with biomedical problems on the micro-scale.
Candidate polymers for the production of MEMS are polycarbonate (PC), polymethylmethacrylate (PMMA), polyvinylchloride (PVC), polyethylene (PE) and Polydimethylsiloxane.
Additionally, Polydimethylsiloxane is the most commonly used material in the manufacturing of microfluidic devices, which are an important technology for the development of systems such as drug delivery, DNA sequencing, clinical diagnostics, point of care testing and chemical synthesis.
The used materials in these systems should be biocompatible, optically transparent and provide fast prototyping and low fabrication cost, features found in Polydimethylsiloxane.
-Surfactants and antifoaming agents:
Polydimethylsiloxane derivatives are common surfactants and are a component of defoamers.
Polydimethylsiloxane, in a modified form, is used as an herbicide penetrant and is a critical ingredient in water-repelling coatings, such as Rain-X.
-Daytime radiative cooling:
Polydimethylsiloxane is a common surface material used in passive daytime radiative cooling as a broadband emitter that is high in solar reflectivity and heat emissivity.
Many tested surfaces use Polydimethylsiloxane because of its potential scalability as a low-cost polymer.
As a daytime radiative cooling surface, Polydimethylsiloxane has also been tested to improve solar cell efficiency.
-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 Polydimethylsiloxane, and the optically clear PDMS permits the projected image to pass through to the resin undistorted.
-Medicine and cosmetics:
Activated dimethicone, a mixture of polydimethylsiloxanes and silicon dioxide (sometimes called simethicone), is often used in over-the-counter drugs as an antifoaming agent and carminative.
Polydimethylsiloxane also works as a moisturizer that is lighter and more breathable than typical oils.
Silicone breast implants are made out of a Polydimethylsiloxane elastomer shell, to which fumed amorphous silica is added, encasing PDMS gel or saline solution.
The use of Polydimethylsiloxane in the manufacture of contact lenses was patented (later abandoned).
-Skin:
Polydimethylsiloxane is used variously in the cosmetic and consumer product industry as well.
For example, dimethicone is used widely in skin-moisturizing lotions where Polydimethylsiloxane 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.
-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 (especially for damaged hair), and are even more conditioning to the hair than common dimethicone and/or dimethicone copolyols.
-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.
-As anti-parasitic:
Polydimethylsiloxane is effective for treating lice in humans.
This is thought to be due not to suffocation (or poisoning), but to Polydimethylsiloxane's blocking water excretion, which causes insects to die from physiological stress either through prolonged immobilisation or disruption of internal organs such as the gut.
Polydimethylsiloxane is the active ingredient in an anti-flea preparation sprayed on a cat, found to be equally effective to a widely used more toxic pyriproxifen/permethrin spray.
The parasite becomes trapped and immobilised in Polydimethylsiloxane, inhibiting adult flea emergence for over three weeks.
-Foods:
Polydimethylsiloxane is added to many cooking oils (as an anti-foaming 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 and Wendy's french fries.
Under European food additive regulations, Polydimethylsiloxane is listed as E900.
-Domestic and niche uses:
Many people are indirectly familiar with PDMS because it is an important component in Silly Putty, to which Polydimethylsiloxane imparts its characteristic viscoelastic properties.
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 can be used as a sorbent for the analysis of headspace (dissolved gas analysis) of food.
HOW TO USE POLYDIMETHYLSILOXANE:
Because Polydimethylsiloxane have special and excellent physical and chemical function, it can be used in many different industries:
1. Polydimethylsiloxane is used cosmetic industry for skin care cream, bath gel, shampoo and other cosmetic formulations with excellent softness and silky feel.
2. Polydimethylsiloxane is used rubber, plastic, latex, polyurethane, light industry: as a model release agent, brightener agent and release agent of some rubber, plastic, latex , polyurethane products and handicraft production.
3. Polydimethylsiloxane is used machinery, automotive, instrumentation, electronics and other industries used as high-grade lubricants, liquid springs, cutting fluids, buffers oil, transformer oil, high temperature brake fluid, brake fluid, instrumentation damping oil, mold release agents and other modeling framework.
4. Polydimethylsiloxane is used textile, apparel industry as a softener, water repellent, feel modifiers, sewing thread lubrication, chemical fiber spinneret pressure lubrication and clothing lining additives.
5. Add Polydimethylsiloxane to other additives in leather and leather chemicals industry, it can be used as softeners, water repellent, feel agents, defoamers, brighteners.
6. Polydimethylsiloxane is used pharmaceutical, food, chemical, paint , building materials industry as defoamers, lubricants, and other weather-resistant paint.
7. Polydimethylsiloxane is used other specific purposes and other new materials.
APPLICATIONS FOR MICRO-FLUIDIC SYSTEMS, POLYDIMETHYLSILOXANE:
Polydimethylsiloxane is a widely-used and versatile ingredient seen in many skin care and beauty products because of its ability to serve as an anti-foaming agent, skin protectant and conditioner; it is known to prevent water and moisture loss in the skin by forming a hydrating barrier.
According to research published in Skin Research and Technology, this barrier also serves as a mild water repellent, and has been shown to fill in fine lines, giving skin a temporary “plump” look.
Polydimethylsiloxane is an easily spreadable silicone oil that creates a coating when applied to the skin that feels smooth and silky to the touch, although this effect is superficial.
FEATURE AND ADVANTAGES OF POLYDIMETHYLSILOXANE:
1. Smoothness & softness & hydrophobicity & good chemical stability & insulation property.
2. High and low temperature resistance & high flash point.
3. Low freezing point (it can be chronically used in the temperature from -50℃ to +200 ℃).
4. Small viscosity-temperature coefficicent & big compression ratio & low surface tension.
ADVANTAGES OF POLYDIMETHYLSILOXANE:
Silicone oil is a colorless, odorless, non-toxic and non-irritating products, chemical stability, heat resistance, cold resistance, water repellency, lubricity, high refraction, storage stability and compatibility with commonly used cosmetic ingredients.
BENEFITS OF PLASMA PRE-TREATMENT OF MICRO-FLUIDIC SYSTEMS, POLYDIMETHYLSILOXANE:
*Short process time
*Irreversible connections of PDMS to the substrate surface, thus formation of impermeable channels in the micro-fluidic component
*Hydrophiling of the PDMS and the substrate surface for complete wetting of the channels
*Formation of hydrophilic-hydrophobic areas
PROPERTIES OF POLYDIMETHYLSILOXANE:
Silicon, glass and polymers are the typical materials used for micro devices fabrication: silicon, because of its thermal conductivity and the availability of advanced fabrication technologies; glass, mainly due to its transparency; polymers, because of its low cost, optical transparency and flexibility.
Compared to glass and silicon, Polydimethylsiloxane turns out to be the most promising elastomer, because the other two materials have a high manufacturing cost, require greater labour intensity and are rigid in nature.
The variable elasticity of Polydimethylsiloxane in medical applications is also favourable; its modulus of elasticity is 1–3 MPa (compared to ~50 GPa of glass).
Polydimethylsiloxane is also chemically inert, thermally stable, permeable to gases, simple to handle and manipulate, exhibits isotropic and homogeneous properties and can replicate submicron features to develop microstructures.
Additionally, this elastomer is optically transparent, can work as a thermal and electrical insulator and degrades quickly in the natural environment.
Polydimethylsiloxane presents a hyperelastic behaviour, which is the ability of a material to undergo large deformations before rupture.
This characteristic is also found in biological tissues and, for that reason, Polydimethylsiloxane is a well-suited material to mimic, for example, blood vessels.
Another characteristic of this elastomer is its biocompatibility, which means that Polydimethylsiloxane is compatible with biologic tissues.
Polydimethylsiloxane presents a transmittance up to 90% for the wavelength from 390 nm to 780 nm and, due to this characteristic, PDMS-based microsystems allow the direct observation of the mimicked blood flow inside the mimicked vessels and the integration of optical detection systems, hence playing an important role in this field.
With the purpose of extending the lifespan of a chip, Polydimethylsiloxane is used to embed or encapsulate electronic components by casting.
Due to its thermal and electrical insulation capability, Polydimethylsiloxane protects the components from environmental factors and mechanical shock within a large temperature range (−50–200 °C).
Despite these advantages, Polydimethylsiloxane has some properties that can present a limitation in some applications.
Due to its CH3 groups, Polydimethylsiloxane presents a hydrophobic surface (contact angle with water ~108° ± 7°), often limiting its application in solutions composed of biological samples.
Additionally, Polydimethylsiloxane tends to swell when combined with certain reagents.
In some applications, the absorption of small molecules flowing through the channels makes it difficult to quantitatively analyse experiments in proteomic drug discovery and cell culture.
In microchannels, the hydrophobicity of Polydimethylsiloxane generates complications that include impedance to the flow of polar liquids, which makes it difficult to wet its surface with aqueous solvents.
On the other hand, much effort has been made to make the Polydimethylsiloxane surface hydrophilic and resistant to protein adsorption.
Strategies employed in attempting to solve Polydimethylsiloxane hydrophobicity include surface activation methods such as: oxygen plasma; UV/ozone treatments; corona discharges, which are widely used for PDMS surface oxidation to promote microchannel wettability.
The main benefits of these methods are the short treatment time and easy operation; however, the Polydimethylsiloxane surface recovers its hydrophobicity when in contact with air within a few minutes.
Another method is physisorption, which is a simple and efficient approach that relies on surface hydrophobic or electrostatic interactions.
This method includes the following techniques: layer-by-layer deposition; non-ionic surfactants; charged polymers.
The disadvantages are the lack of covalent bonds between Polydimethylsiloxane and surface modifiers, which lead to the loss of modifiers quickly through desorption.
In order to improve the difficulties encountered in physisorption, chemical modification methods allow for maintaining a long-term stability of the modified surface.
These methods include: chemical vapor deposition, surface segregation and self-assembled monolayers, silanization, and polymer brushes via grafting methods.
Adding waxes such as paraffin or beeswax to Polydimethylsiloxane has been demonstrated to potentially increase the corrosion resistance, hydrophobicity and thermal and optical properties of Polydimethylsiloxane, which is useful in applications such as sensors, wearable devices and superhydrophobic coating
SOFT LITHOGRAPHY, POLYDIMETHYLSILOXANE:
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.
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, Polydimethylsiloxane 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.
The popularity of Polydimethylsiloxane in microfluidics area is due to its excellent mechanical properties.
Moreover, compared to other materials, Polydimethylsiloxane possesses superior optical properties, allowing for minimal background and autofluorescence during fluorescent imaging.
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 are left imprinted in the Polydimethylsiloxane.
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 Polydimethylsiloxane, 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.
Polydimethylsiloxane can be cross-linked into networks and is a commonly used system for studying the elasticity of polymer networks.
Polydimethylsiloxane can be directly patterned by surface-charge lithography.
Polydimethylsiloxane is being used in the making of synthetic gecko adhesion dry adhesive materials, to date only in laboratory test quantities.
Some flexible electronics researchers use Polydimethylsiloxane because of its low cost, easy fabrication, flexibility, and optical transparency.
Yet, for fluorescence imaging at different wavelengths, Polydimethylsiloxane shows least autofluorescence and is comparable to BoroFloat glass.
STRUCTURE OF POLYDIMETHYLSILOXANE:
The chemical formula of Polydimethylsiloxane is CH3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [Si(CH3)2O] units.
Industrial synthesis can begin from dimethyldichlorosilane and water by the following net reaction:
n Si(CH3)2Cl2 + (n + 1) H2O → HO[−Si(CH3)2O−]nH + 2n HCl
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.
CHEMICAL COMPATIBILITY OF POLYDIMETHYLSILOXANE:
Polydimethylsiloxane is hydrophobic.
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.
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.
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.
Despite this, some organic solvents lead to sufficiently small swelling that they can be used with Polydimethylsiloxane, for instance within the channels of PDMS 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.
CHEMISTRY OF POLYDIMETHYLSILOXANE:
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.
Polydimethylsiloxane 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 Polydimethylsiloxane having an unusually high level of viscoelasticity.
MECHANICAL PROPERTIES OF POLYDIMETHYLSILOXANE:
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 Polydimethylsiloxane'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 (\tan\delta\ll0.001).
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), Polydimethylsiloxane acts like an elastic solid, similar to rubber.
Viscoelasticity is a form of nonlinear elasticity that is common amongst noncrystalline polymers.
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 Polydimethylsiloxane, 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.
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, Polydimethylsiloxane 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.
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.
Polydimethylsiloxane is widely known to be easily stretched, bent, compressed in all directions.
Depending on the application and field, the user is able to tune the properties based on what is demanded.
Overall Polydimethylsiloxane has a low elastic modulus which enables it to be easily deformed and results in the behavior of a rubber.
Viscoelastic properties of Polydimethylsiloxane can be more precisely measured using dynamic mechanical analysis.
This method requires determination of Polydimethylsiloxane's flow characteristics over a wide range of temperatures, flow rates, and deformations.
Because of Polydimethylsiloxane'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)
CHEMICAL COMPATIBILITY OF POLYDIMETHYLSILOXANE:
After polymerization and cross-linking, solid Polydimethylsiloxane samples will present an external hydrophobic surface.
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.
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, 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 PDMS 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.
BRANCHING AND CAPPING OF POLYDIMETHYLSILOXANE:
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)2OSi(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 PDMS 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.
Polydimethylsiloxane is manufactured in multiple viscosities, 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 Polydimethylsiloxane' unusually high level of viscoelasticity.
SAFETY AND ENVIRONMENTAL CONSIDERATIONS OF POLYDIMETHYLSILOXANE:
According to Ullmann's Encyclopedia of Industrial Chemistry, 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.
Polydimethylsiloxane's degradation is catalyzed by various clays.
SOME CHEMISTRY, POLYDIMETHYLSILOXANE:
A little bit of chemistry will help us better understand the advantages and drawbacks of Polydimethylsiloxane for microfluidic applications.
Polydimethylsiloxane empirical formula is (C2H6OSi)n and its fragmented formula is CH3[Si(CH3)2O]nSi(CH3)3, n being the number of monomers repetitions.
FORMULA OF POLYDIMETHYLSILOXANE:
Depending on the size of monomers chain, the non-cross-linked Polydimethylsiloxane may be almost liquid (low n) or semi-solid (high n).
The siloxane bonds result in a flexible polymer chain with a high level of viscoelasticity.
After “cross-linking”
Polydimethylsiloxane becomes a hydrophobic elastomer.
Polar solvents, such as water, struggle to wet the Polydimethylsiloxane (water beads and does not spread) and this leads to the adsorption of hydrophobic contaminants from water on the material’s surface.
OXIDATION OF POLYDIMETHYLSILOXANE:
Polydimethylsiloxane oxidation using plasma changes the surface chemistry, and produces silanol terminations (SiOH) on its surface.
This helps making the material hydrophilic for thirty minutes or so.
This process also makes the surface resistant to the adsorption of hydrophobic and negatively-charged molecules.
In addition, its plasma oxidation is used to functionalize the surface with trichlorosilane or to covalently bond Polydimethylsiloxane (at the atomic scale) on an oxidized glass surface by the creation of a Si-O-Si bonds.
Whether the surface is plasma oxidized or not, Polydimethylsiloxane does not allow water, glycerol, methanol or ethanol infiltration and consecutive deformation.
Thus, it is possible to use Polydimethylsiloxane with these fluids without fear of micro-structure deformation.
However, Polydimethylsiloxane deforms and swells in the presence of diisopropylamine, chloroform and ether, and also, to a lesser extent, in the presence of acetone, propanol and pyridine – therefore, Polydimethylsiloxane is not ideal for many organic chemistry applications.
POLYDIMETHYLSILOXANE IN MICROFLUIDICS:
Polydimethylsiloxane is one of the most employed materials to mold microfluidic devices.
We describe here the fabrication of a microfluidic chip by soft-lithography methods.
(1) The molding step allows mass-production of microfluidic chips from a mold.
(2) A mixture of PDMS (liquid) and crosslinking agent (to cure it) is poured into the mold and heated at high temperature.
(3) Once it has hardened, it can be taken off the mold.
We obtain a replica of the micro-channels on the block.
Microfluidic device completion:
(4) To allow the injection of fluids for future experiments, the inputs and outputs of the microfluidic device are punched with a Polydimethylsiloxane puncher the size of the future connection tubes.
(5) Finally, the face of the block of Polydimethylsiloxane with micro-channels and the glass slide are treated with plasma.
(6) The plasma treatment allows Polydimethylsiloxane and glass bonding to close the microfluidic chip.
The chip is now ready to be connected to microfluidic reservoirs and pumps using microfluidic tubing.
Tygon tubing and Teflon tubing are the most commonly used tubings on microfluidic setups.
FORM OF POLYDIMETHYLSILOXANE:
1. Clear, colorless, odorless fluids
2. High Viscosities
3. Non-Flammable
4. High Damping action
5. Low Temperature stability
6. High Temperature Stability
7. Little viscosity change at temperature
8. Inert to virtually all o-rings, gaskets, seals and valves
9. Excellent lubrication
10. High oxidation resistance
11. High dielectric strength
12. High water repellency
13. High Shear resistance
14. High molecular weight
15. Although not recommended for silicone o-rings
PHYSICAL and CHEMICAL PROPERTIES of POLYDIMETHYLSILOXANE:
Chemical formula: CH3[Si(CH3)2O]nSi(CH3)3
Density: 0.965 g/cm3
Melting point: N/A, vitrifies
Boiling point: N/A, vitrifies
Physical state: clear, liquid
Color: colorless
Odor: odorless
Melting point/freezing point:
Melting point: -50 °C
Initial boiling point and boiling range: 35 °C at 1.013 hPa
Flammability (solid, gas): No data available
Upper/lower flammability or explosive limits: No data available
Flash point: 321 °C - closed cup
Autoignition temperature: No data available
Decomposition temperature: No data available
pH: No data available
Viscosity
Viscosity, kinematic: No data available
Viscosity, dynamic: No data available
Water solubility: No data available
Partition coefficient: n-octanol/water: No data available
Vapor pressure: 7 hPa at 20 °C
Density: 0,76 - 0,97 g/cm3
Relative density: No data available
Relative vapor density: No data available
Particle characteristics: No data available
Explosive properties: No data available
Oxidizing properties: none
Other safety information: No data available
GENERAL PROPERTIES OF POLYDIMETHYLSILOXANE:
1. Name: Dimethyl Silicone Fluid
2. Model No.: AS-201#
3. Appearance: colorless, clear, transparent liquid
4. Smell: Odorless
5. Viscosity (25°C): 50～1,000,000 cSt
6. Specific Gravity (25°C): 0.955～0.978 g/cm3
7. Volatile Matter Content (150°C/24hr): ≤1.5%
8. Refractive Index (25°C): 1.390～1.410
9. Flash Point: 260°C～300°C
10. Pour Point: -50°C
11. Viscosity Temperature Coefficient: 0.59~0.61
12. Coefficient of Expansion: 0.00094~0.00104 cc/cc/°C
13. Thermal Conductivity (25°C): 0.10~0.16
14. Dielectric Constant (25°C, 50Hz): 2.60-2.80
15. Dielectric Loss Factor(25°C, 50Hz): ≤1.0×104
16. Volume Resistivity: ≥1.0×1015 Ω·cm
17. Breakdown Voltage: ≥1.0 KV/mm
18. Recommended dosage: 1~3%
FIRST AID MEASURES of POLYDIMETHYLSILOXANE:
-Description of first-aid measures:
*If inhaled:
After inhalation:
Fresh air.
*In case of skin contact:
Take off immediately all contaminated clothing.
Rinse skin with water/ shower.
*In case of eye contact:
After eye contact:
Rinse out with plenty of water.
Remove contact lenses.
*If swallowed:
After swallowing:
Make victim drink water (two glasses at most).
Consult doctor if feeling unwell.
-Indication of any immediate medical attention and special treatment needed:
No data available
ACCIDENTAL RELEASE MEASURES of POLYDIMETHYLSILOXANE:
-Environmental precautions:
Do not let product enter drains.
-Methods and materials for containment and cleaning up:
Cover drains.
Collect, bind, and pump off spills.
Observe possible material restrictions.
Take up with liquid-absorbent material.
Dispose of properly.
Clean up affected area.
FIRE FIGHTING MEASURES of POLYDIMETHYLSILOXANE:
-Extinguishing media:
*Suitable extinguishing media:
Foam
Carbon dioxide (CO2)
Dry powder
*Unsuitable extinguishing media:
For this substance/mixture no limitations of extinguishing agents are given.
-Further information:
Suppress (knock down) gases/vapors/mists with a water spray jet.
Prevent fire extinguishing water from contaminating surface water or the ground water system.
EXPOSURE CONTROLS/PERSONAL PROTECTION of POLYDIMETHYLSILOXANE:
-Control parameters:
--Ingredients with workplace control parameters:
-Exposure controls:
--Personal protective equipment:
*Eye/face protection:
Use equipment for eye protection
Safety glasses
*Skin protection:
not required
*Respiratory protection:
Not required.
-Control of environmental exposure:
Do not let product enter drains.
HANDLING and STORAGE of POLYDIMETHYLSILOXANE:
-Conditions for safe storage, including any incompatibilities:
*Storage conditions:
Tightly closed.
STABILITY and REACTIVITY of POLYDIMETHYLSILOXANE:
-Chemical stability:
The product is chemically stable under standard ambient conditions (room temperature) .
-Possibility of hazardous reactions:
No data available
-Incompatible materials:
No data available
SYNONYMS:
poly(dimethylsiloxane)
PDMS
dimethicone
dimethylpolysiloxane
E900
Poly(dimethylsiloxane)
dimethylpolysiloxane
dimethylsilicone fluid
dimethylsilicone oil
dimethicone
INS No. 900a
