What Is Dimethicone?

Dimethicone, also known as polydimethylsiloxane (PDMS), is a silicone oil with special attributes that make it a useful component in many skin and hair care products. It has numerous industrial applications as well, and is even a good additive in some foods. People widely use products that contain the compound, and generally report very few adverse effects, although some individuals do have sensitivities to it.

Use in Personal Care Products

Products such as hair conditioners and shampoos often include dimethicone to facilitate the combing of tangled hair, as well as to give hair a better shine. It forms a slick lubricating coat around each strand of hair so that a comb will move through the hair with significantly less resistance. Also, it acts as a skin protectant and emollient, showing up as an component in many over-the-counter moisturizing lotions and skin creams, as well as in many makeup products. Even diaper rash creams for babies often add this chemical in order to relax the irritated skin.

Safety

The U.S. Food and Drug Administration (FDA) has authorized adding PDMS to products such as those listed above, and years of consumer use have shown it to be mostly safe. One area that has brought up concern is the usage of the chemical as a filling for breast implants. For years, PDMS silicone implants were the standard, although recent medical issues have brought on a gradual shift to implants filled with saline.

Expectant and breast-feeding mothers are advised to check with a physician before using any product that has dimethicone. It is possible for a consumer to find out if dimethicone, or one of its variants, is present in a particular product by going over the list of components. Names such as Amodimethicone, Stearoxy Dimethicone and Behenoxy Dimethicone indicate the usage of polymers based on this man-made compound.

Side Effects

A few side effects have been reported from the use of PMDS products; they include gentle itching and stinging or perhaps burning sensations. Allergic reactions such as hives, unexpected breathing difficulties, and swelling in any part of the mouth or face represent can also happen. Users of dimethicone creams may be shocked to find that the product can actually worsen dryness in some individuals. This is not necessarily a sign of ineffectiveness, but may alternatively reveal an allergic reaction that should not be disregarded.

Should such symptoms show up, doctors advise immediately stopping use of the product. Looking for medical assistance is a good idea if the reaction results in being serious, or does not improve quickly. A pharmacist can be another good source for guidance relating to side effects.

Other Uses

Dimethicone is widely used in non-cosmetic products as well. Because of its corrosion-inhibiting qualities, it is a well-known additive in commercial lubricants. Manufacturers of processed foods use the compound to prevent caking and foaming. It is also the primary ingredient in the world-famous toy known as Silly Putty.

Composition

Silicon dioxide, commonly referred to as silicon or silica, is a naturally occurring element in the earth. Chemists have efficiently combined silica with oxygen, hydrogen, and carbon. These chemical compounds, which may also include additional elements, are known as silicone polymers, or simply silicones. A polymer is a large molecule that is composed of units of smaller molecules that are repeated in a molecular chain. Not all silicones are identical; they vary depending on how the manufacturer combines and fuses the elements together. To avoid misunderstandings, remember that “silicone” is a product derived from “silicon.”

Physical Characteristics

PMDS is unusual in that it tends to share some of the properties of both a solid and a liquid. Chemists refer to this quality as viscoelastic. At room temperature, a solid mass of the product will at first feel and behave very much like rubber. If left on a solid area over several hours, even so, it will eventually ooze outward to cover the whole area. A person can then peal it off to reveal a perfect mold of the object. This semi-solid state is in part what makes the compound so versatile.

Polydimethyl siloxane

Polydimethylsiloxane (PDMS) belongs to a group of polymeric organosilicon substances that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its strange rheological (or flow) properties. PDMS is optically clear, and, in general, is considered to be inert, non-toxic and non-flammable. It is often called dimethicone and is one of several types of silicone oil (polymerized siloxane).

Its applications range from contact lenses and medical devices to elastomers; it is present, also, in shampoos (as dimethicone makes hair shiny and slippery), food (antifoaming agent), caulking, lubricating oils, and heat-resistant tiles.

Chemistry

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

n Si(CH3)2Cl2 + n H2O ? [Si(CH3)2O]n + 2n HCl

During polymerization, this reaction builds up potentially dangerous hydrogen chloride gas. For medical uses, a process was developed in which 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 treating procedure 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. Under perfect circumstances, each and every 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 control molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain.

The polymer is manufactured in various viscosities, ranging from a thin pourable liquid (when n is very low), to a dense rubbery semi-solid (when n is very high). PDMS molecules have rather 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 turn out to be loosely entangled when molecular weight is high, which results in PDMS’ uncommonly high level of viscoelasticity.

Mechanical qualities

PDMS is viscoelastic, meaning that at long flow times (or high temperatures), it behaves like a viscous liquid, similar to honey. However, at short flow times (or low temperatures), it behaves like an elastic solid, similar to rubber. In other words, if some PDMS is left on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface flaws. Even so, if the same PDMS is rolled into a sphere and thrown onto the same surface (short flow time), it will bounce like a rubber ball.

Although the viscoelastic attributes of PDMS can be naturally observed using the simple experiment explained above, they can be more accurately measured using dynamic mechanical analysis. This involves using a specialized instrument to determine the material’s flow properties 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 PDMS varies with preparation conditions, but is typically in the range of 100 kPa to 3 MPa. The loss tangent is very low (tan d « 0.001).

Chemical compatibility

After polymerization and cross-linking, solid PDMS samples will present an external hydrophobic surface. This surface will appear metallic and shiny, although the substrate is clear. This surface chemistry makes it difficult for polar solvents (such as water) to wet the PDMS 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 PDMS surface hydrophilic, allowing water to wet (this is regularly required for 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 specific time hydrophobic recovery of the surface is unavoidable independently of the surrounding medium whether it is vacuum, air, or water.

Solid PDMS samples (whether surface oxidized or not) will not permit aqueous solvents to infiltrate and swell the material. Hence PDMS structures can be used in combination with water and alcohol solvents without material deformation.
Nevertheless the majority of organic solvents will diffuse into the material and make it swell,[3] making them incompatible with PDMS devices. Despite this, several organic solvents lead to sufficiently small swelling that they can be used with PDMS, 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 PDMS to the greatest extent; solvents such as chloroform, ether, and THF swell the material to a significant level. Solvents such as acetone, 1-propanol, and pyridine swell the material to a small level. Alcohols and polar solvents such as methanol, glycerol and water do not swell the material appreciably.

Applications

Many people are in a roundabout way familiar with PDMS because it is an important 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. PDMS is also used as a element 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. PDMS has also been used as a filler fluid in breast implants, although this exercise has diminished considerably, due to safety issues.

Industrial uses

Dimethicone is also the active silicone fluid in automotive viscous limited slip differentials and couplings. This is usually a non-serviceable OEM element but can be replaced with mixed performance results due to variances in effectiveness caused by refill weights or non-standard pressurisations.

PDMS is commonly used as a stamp resin in the procedure of soft lithography, making it one of the most typical components used for flow delivery in microfluidics chips. The process of soft lithography consists of producing an elastic stamp, which allows 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 create devices that can be used in the areas of optic telecommunications or biomedical investigation. Nevertheless, this process still cannot be used for the industrial production of electronic components. In fact, the patterns are acquired by the process of stamping thanks to a shape (or stamp). This stamp is produced from the normal methods of photolithography or electron-beam technology. The resolution depends on the mask used and can reach 6 nm.

In Bio-MEMS, soft lithography is used thoroughly for microfluidics in both organic and inorganic contexts. Silicon wafers are used to design channels, and PDMS is then poured over these wafers and left to harden. When taken off, even the smallest of details is left imprinted in the PDMS. With this particular PDMS block, hydrophilic surface modification is conducted using RF Plasma techniques. Once surface bonds are disrupted, usually a piece of glass slide is placed on the activated side of the PDMS (the side with imprints). Once the bonds relax to their normal state, the glass is completely sealed to the PDMS, hence creating a water-resistant channel. With these devices, investigators can utilize numerous surface chemistry techniques for various functions creating unique lab-on-a-chip devices for rapid parallel testing.

PDMS can be cross-linked into networks and is a commonly used system for studying the elasticity of polymer networks. PDMS can be directly designed by surface-charge lithography. PDMS is being used in the making of artificial Gecko adhesion dry adhesive materials, to date only in laboratory test quantities.

Medicine and cosmetics

Activated dimethicone, a mixture of polydimethylsiloxanes and silicon dioxide (sometimes called simethicone), is used in over-the-counter drug as an antifoaming agent and carminative.
PDMS is used variously in the cosmetic and consumer product business as well. For example, PDMS can be used in the treatment of head lice and dimethicone is used extensively in skin-moisturizing products where it is listed as an active component whose function 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.”

Other

This silicone can be found in several processed foods and fast food items such as McDonald’s Chicken McNuggets and Wendy’s French fries. PDMS is also used in analytical chemistry as a component of some types of SPME fibers. PDMS in a modified form is used as an herbicidal penetrant and is a critical component in water-repelling coatings, such as Rain-X

Uses of Dimethicone

This medication is used as a moisturizer to treat or protect against dry, rough, scaly, itchy skin and mild skin irritations (e.g., diaper rash, skin burns from radiation therapy). Emollients are materials that make softer and hydrate the skin and decrease itching and flaking. A few products (e.g., zinc oxide, white petrolatum) are used mainly to protect the skin against irritation (e.g., from wetness).

Dry skin is caused by a loss of water in the upper layer of the skin. Emollients/moisturizers work by creating an oily coating on the top of the skin which contains water in the skin. Petrolatum, lanolin, mineral oil and dimethicone are common emollients. Humectants, such as glycerin, lecithin, as well as propylene glycol, draw water into the outer layer of skin. Numerous products also have ingredients that make softer the horny chemical (keratin) that holds the top layer of skin cells together (e.g., urea, alpha hydroxy acids such as lactic/citric/glycolic acid, and allantoin). This helps the dead skin cells fall off,  the skin keep in more water, and leaves the skin feeling smoother and much softer.

How to use dimethicone

Use this product as guided. Many products require priming prior to use. Follow all instructions on the product package. If you are unsure about any of the information, consult your doctor or pharmacist. Several products need to be shaken prior to use. Check the label to see if you should shake the bottle well before using. Apply to the affected areas of the skin as needed or as directed on the label or by your doctor. How often you apply the medicine will depend on the product and your skin condition. To treat dry hands, you may need to use the product every time you wash your hands, applying it throughout the day.

If you are using this product to help treat diaper rash, thoroughly clean the diaper area well before use and allow the area (blank) dry before applying the product.

If you are using this product to help treat radiation skin burns, check with radiation personnel to see if your product can be applied before radiation therapy.

Follow all the instructions on the label for proper use. Apply to the skin only. Stay away from sensitive places such as your eyes, inside your mouth/nose, and the vaginal/groin area, except if the label or your doctor directs you otherwise. Check the label for instructions about any areas or types of skin where you should not apply the product (e.g., on the face, any areas of broken/chapped/cut/irritated/scraped skin, or on a recently shaved area of the skin). Consult your doctor or pharmacist for more details.

Use this medication on a regular basis to get the most benefit from it. The majority of moisturizers require water to work well. Apply the product after bathing/showering while the skin is still damp. For very dry skin, your doctor may advise you to soak the area before using the product. Long, hot, or frequent bathing/washing can aggravate dry skin.

If your problem continues or gets worse, or if you consider you may have a serious medical problem, seek immediate medical attention.

Side Effects

Most emollients can be used safely and properly with no side effects. However, burning, stinging, inflammation, or irritation may occur. If any of these effects continue or get worse, tell your doctor or pharmacist immediately.
If your doctor has recommended this medication, remember that he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have significant side effects.
Tell your doctor immediately if any of these unlikely but serious side effects happen: uncommon changes in the skin (e.g., turning white/soft/soggy from too much wetness), signs of skin infection.
A very severe allergic reaction to this drug is rare. Even so, get immediate medical attention if you notice any symptoms of a severe allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, difficulties breathing.

This is not a complete list of possible side effects. If you notice other effects not listed previously mentioned, contact your doctor or pharmacist.

Precautions

Before using this product, tell your doctor or pharmacist if you are allergic to any of the components in the product; or if you have any additional allergies. This product may contain inactive ingredients, which can trigger allergic reactions or other problems. Talk to your pharmacist for more details.

Should you have any of the following health problems, consult your doctor or pharmacist before using this product: skin cuts/infections/sores.

Some elements (e.g., preservatives, fragrance) may make you more sensitive to the sun. Examine the label for any safety measures or ask your doctor or pharmacist if you need to take any specific measures when in the sun. Your doctor/pharmacist may suggest using a sunscreen, wearing protective clothing when outside, and avoiding extented sun exposure, tanning booths, and sunlamps.

Some products might aggravate acne. If your skin is prone to acne breakouts, look for the word “non-comedogenic” (will not clog pores) on the label. Many products may stain/discolor clothing. Ask your doctor or pharmacist for more details.

It is not well-known if this drug passes into breast milk. Consult your doctor before breast-feeding, especially if you are applying this product to the breast area.

Interactions

If you are using this product under your doctor’s direction, your doctor or pharmacist may already be aware of possible medicine interactions and may be checking you for them. Do not start, stop, or change the dosage of any medicine before reviewing with your doctor or pharmacist first.

If your doctor has instructed you to use this product, or if you use any prescribed product on the skin, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, including other skin care products.

Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

Overdose

This medication may be dangerous if swallowed. If swallowing or overdose is suspected, contact your local poison control center or even emergency room right away.

Notes

Some ways to help avoid dry skin include using lukewarm (not hot) water when bathing, taking baths/showers less often (e.g., every 1-2 days), keeping baths/showers short, and using a humidifier when the air is very dry.

There are many types of emollient products accessible. A few contain fragrance or other ingredients that some people may be sensitive to. Emollients are available in different forms such as oils, creams, lotions, or sprays. Consult with your doctor or pharmacist on the product that may be best for you.

Missed dose

If you are using this product on a regular routine and miss a dose, use it as soon as you remember. Do not use more product or use it more often than directed to catch up.

Storage

Refer to storage information printed on the package. If you have any questions regarding storage, ask your pharmacist. Keep all drug products away from children as well as pets.

Do not store the foam container close to high heat (more than 120 degrees F/49 degrees C), and do not store or use it near an open flame. Because foam canisters are under pressure, do not puncture or burn the container.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer necessary. Consult your pharmacist or local waste disposal company for more details about how to properly dispose of your product.