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How Does UV Gel Work? A Basic Chemistry Lesson

How Does UV Gel Work?
A Basic Chemistry Lesson

I am not going to enter into a discussion on the exact chemicals that are used in both types of systems that I am covering in this guide. We can find it sufficient to say that most people in our industry (not the chemists, but others such as instructors) think of the chemistry between acrylics and gels to be similar. This is partly true but not quite as simple. While it is true that the resins used in each system react using a polymerization reaction called a free radical reaction (a free radical reaction if a reaction in which double bonds (ethylene bonds) are broken and then reformed with other ethylene bonds), this is where the similarities end. Acrylic plastics are, by definition, plastics that are formed by the polymerization reaction of acrylic acid monomers.

Acrylic acid monomers are short carboxylic acids (the acid in vinegar is also a carboxylic acid) that contain an ethylene functional group (an ethylene functional group is formed between two carbon atoms that share two bonds) that is involved in the free radical polymerization reaction. Some of the acidic monomers are di-funtional, meaning that they are two functional ethylene groups while others can have three or more reaction sites. It is also common to use resins that have only one functional group. These mono-functional resins are also called chain terminators – resins that are used to stop polymerization chain formation. These resins are useful to increase flexibility or to make the finished compound a thinner viscosity (viscosity is the measurement of the thickness or thinness of a liquid).

Acrylics polymerization reaction is started with the use of a catalyst called peroxide. The peroxide that is used in acrylics is benzoyl peroxide. A catalyst is a chemical that initiates a reaction without changing it own form. The peroxide that acrylic systems use is called benzoyl peroxide – the same chemical that is used in acne creams. The benzoyl peroxide is a dry powder that is mixed with the acrylic powder. It is this acrylic powder that is mixed with the acrylic acid monomers that will create the acrylic plastic in the reaction that forms the acrylic nail.

Gels polymerize using the same type of free-radical reaction but the functional groups are usually attached to a larger resinous backbone such as a urethane backbone. These types of resins are termed oligomers. Oligomers are generally accepted as being safer to handle and are also thicker in viscosity than the acrylic acid monomers. One advantage that UV gels have over acrylics is that they are single component systems that do not begin to react until they are exposed to UV light. UV light (or Ultra Violet light) is light that is in a wavelength that varies between 220 and 420 nanometers (nm). It is most common for UV gels to use a UV light source that produces light in the 350 nm region known as UVC. UV gels use chemical known as photoinitiators (a chemical family that initiates a free radical reaction upon exposure to a light source).

Because gels use UV light to initiate and complete the free-radical reaction, the quality of the UV light bulb is crucial. This fact cannot be stressed enough! There are a few very good quality bulbs on the market that are suitable for our industry and many bulbs that are not. The acceptable 9-watt bulbs on the market at this time are Sylvania (UK manufactured), SLI (UK manufactured) and Philips (Poland manufactured). Any other compact fluorescent bulb should not be used. There are a few bulbs that should never be used. These bulbs are Ocius, a generic Chinese bulb (it only reads “9W UV”), and a generic Chinese bulb that reads “9W UV (DC)”. The use of these poor quality bulbs will result in poor gel performance, lifting, cracking and unacceptable curing of pigmented gel systems. The poor quality bulbs do not necessarily cost less nor are they easier to find – they just are not made with the same care that the Sylvania, SLI and Philips bulbs are made with and as such do not perform acceptably. I could and should use other adjectives for these cheaper, lesser quality bulbs, but I must refrain in my descriptions. Please, read between these lines and determine just how I really feel about these poor quality bulbs and never waste your money on these inferior compact fluorescent bulbs. I must take a few lines to delve into a new UV light source. LED technology is now beginning to make progress into our industry. The advantage of LED UV light sources is that the bulbs last a long time, but the disadvantages are significant. LED bulbs are very focused which means that they will only cure a small area. This requires that the fingertip must be in one location every time. It may also take 5 bulbs to cure a single, long fingernail. The L.E.D. bulbs are expensive, so it may cost $100 in bulbs to cure one fingernail. A second issue with current LED technology is a lens is used to assist the bulb to dissipate the light that is generated by the bulb. Most of the materials that are used to make the lens absorb UV light thus decreasing the effectiveness of the bulb. I imagine that the LED technology will improve over time and as it does, the LED bulbs will move more into the UV gel world.

There is one more issue about UV light sources that is so important that it requires its own paragraph. This is the fact that we use a very specific wavelength of light to cure the products used in UV gels. This wavelength is one that our eyes cannot see. So, when the UV bulbs are producing light, they produce both UV and visible spectrum light. The UV bulbs will continue to produce visible light even after they have stopped producing UV light! Yes, that means that even if you think that your lamp is curing the gel – it may not be! You must change your bulbs often in your UV lamp. A full time nail technician who is servicing 30-40 clients per week should plan on changing the bulbs in her/his lamp once every 4 to 6 months. If a nail technician is servicing 15-20 clients per week in gels, she/he should change the bulbs once a year is sufficient (when good quality bulbs are used). Also, UV bulbs are rated to their life expectancy. This is the amount of time that the bulb should work. Most bulbs are rated for a life expectancy of 10,000 hours. This figure is wrong and should not be used! The compact fluorescent bulbs will produce UV light for a maximum of 300 hours of use. I suggest changing the bulbs after 200 hours of use because I have seen large variations of bulb quality in all UV bulbs. It is important to never let your bulbs become insufficient or too weak to cure the gel. If and when this occurs, ALL of the gel will have to be removed once you determine that your bulbs are bad. This will take more time than you may have and time is money! If you are servicing 30 clients per week and you need to remove all of the gel from those clients – you could be looking at an additional 30 hours of work for the week! Using good quality bulbs and changing them frequently could easily avoid this poor performance. Some lamps on the market have a bulb life indicator. The bulb life indicator will tell you when it is time to change your bulbs based on the duration the lamp has been used. This feature will cost you more money when you buy the lamp but could easily pay for itself within the first year!
Gels have a distinct advantage over acrylics in that they have the chemical ability to form very hard polymers, very soft polymers or polymerized plastics that have a complex physical structure. They can also be used to create polymers that have high hardness values while remaining flexible. Acrylic systems do not have the same degree of variability afforded to them. Gels have the ability to drastically resist yellowing upon exposure to UV light because gels can be made from the use of aliphatic resins that will not discolor upon exposure to UV light.

Urethane acrylates are the main resin of choice when formulating UV gel systems because they have wonderful properties for adhesion, resistance to discoloration, clarity, viscosity and tough polymer formation that imparts exceptional abrasion resistance and gloss. Urethanes can be made to be very flexible or very hard. Urethanes can also be cross-linked during the polymerization reaction to increase chemical resistance and resistance to staining. These are all properties that gels can acquire due to good formulating from a chemist and they are properties that are difficult if not impossible to obtain using acrylic resin an powder systems.

When polymers are formed due to the free radical reaction, the finished polymer may not form for quite some time. When a polymer is reacted, the resins change structure from a liquid to a solid, but the solid has not formed a complete reaction. When polymer chemists want to determine the degree of polymerization of a reaction, we use a tensilometer. Tensilometers test for the total elongation of a polymer as well as the amount of force required to break the polymer into two pieces. The properties of the polymer that this test is able to determine are elongation at break and tensile strength at break. Elongation at break is the ultimate amount of stretch a polymer will have. Tensile strength at break is the amount of force that is required to break the polymer. As a polymer continues to react the physical properties of the plastic will change. Polymer chemists will monitor these changes in a polymer until they become stabilized and at the time of stabilization we can determine that the polymer is done reacting. Acrylic systems often take 30 days to reach this final strength or it takes up to 30 days for an acrylic resin system to fully polymerize! Conversely, gels that have an adequate amount of photoinitiator will take 2-5 minutes to fully cure! The translation for you regarding this issue is this; when your client returns to the salon to have a fill performed on her fingernails, the acrylic is still reacting! When a UV gel fill is done on your clients, the gel is finished polymerizing before she leaves the salon. This makes the gel safer to use for you and your client!

The curing process for gels is very dependant upon the use of a high quality curing lamp and UV bulbs. If a sub-standard lamp and bulbs are used to cure the gel, then the gel will not reach its maximum cure and as such will not be as strong or make it full adhesion potential. Gels that are cured in a lower powered lamp are similar to acrylics that are off-ratio. Acrylics that are mixed too wet or too dry will not obtain their maximum strength and could lift from the fingernail or break easily. So, when you are working with a gel, be certain to use a lamp that the manufacturer recommends and be certain that the bulbs that are used will produce the proper concentration of UV light in the required wavelength to ensure proper polymer formation. When working with an acrylic, practice making the proper ratio of liquid to powder. Improper liquid to powder ratios will lead to polymer failure.

Bonding of the enhancement to the natural nail is obviously critical to the overall performance of the system. We have already reviewed the polymerization reactions and the type of polymerization reaction will determine the type of bonding or primer system that is available to the enhancement to bond to the nail. Acrylics must use an acrylic primer. Acrylic primers are usually acrylic acids that have been chemically treated to be compatible with the chemistry of the fingernail so that the primer will penetrate into the keratin of the fingernail and provide a rooting system for the enhancement to bond. Because the primer is made from carboxylic acids and carboxylic acids are compatible with the oils from the skin, cleansing the fingernail prior to the application of the primer is not as critical as it is with a gel system. Bonding of a gel to the fingernail is more tolerant f the type of primer or bonding system used. Acrylic primers can be used to adhere the enhancement to the fingernail. The reason why this can be done is that both acrylic primers and gels have the same functional group, thus the functional group of the primer will accept the gel resin as a bonding partner and the gel will adhere to the fingernail. Gels are also able to use gel bonding resins. These are resins that are typically less odiferous and do not penetrate as deeply into the fingernail. The advantage to this process is the fingernail is less damaged when the enhancement is unintentionally removed from the fingernail due to lifting or impacting the fingernail to cause it to lift from the natural nail. Gel bonding resins to require an increased amount of care when preparing the fingernail. The fingernail must to cleansed to remove any oils from the nail prior to filing the nail with an emery board. This cleaning to remove oils increases the compatibility of the gel bonding resin with the fingernail. This is important because the gel bonding resin does not use carboxylic acids. Carboxylic acids can comingle with the oils of the fingernail and thus still impart good adhesion. Conversely, gel bonding resins do not contain carboxylic acids that can mix with the fingernail oils, so removal of these oils is crucial.
There are a few crucial terms that are used when we talk about gels. These terms are self-leveling and non-self leveling gels, clear, semi-opaque, building gels, filling gels, and opacity.
“Self-leveling gels” is a concept that is odd for most nail technicians new to gels. The self-leveling gels will do your work for you if you allow them! A self-leveling gel will reach is desired state if you give it enough time. The biggest question is, “how long will that take?” A medium viscosity self-leveling gel will smooth itself within a few minutes depending upon the temperature of the room with respect ot the actual viscosity of the gel at a standard temperature. To make this concept a little simpler, a medium viscosity will reach its optimal shape in 90 seconds at 70 °F or about 20 °C. If the room is warmer than that or if the nail technician is working more slowly, then a thick viscosity self-leveling gel or a thick viscosity non self-leveling gel is preferred. So, if I am working with our 1-Step gel and I find that the gel is constantly running into the sidewall of the fingernail, then I need to use the next thicker gel (ie: change from 1-Step to Extreme Gel or Extreme Gel to Builder gel). Likewise, if I am working with Extreme and I find that the gel is moving too slowly, then I should change to 1-Step.

I often use Super Shiny or Top Gloss to adjust the fingernail enhancement. If I am performing a fill or full-set on a client and the fingernail has a slight dip or thin spot in it, then I will apply a slightly more liberal amount of the Super Shiny or Top Gloss to add thickness to the enhancement to make it more visually appealing. This technique is used to enhance the arch or curve of the fingernail’s enhancement or fill in a dip or shallow area. This is very easy when you are looking at the enhancement during the finishing process while applying the Super Shiny or Top Gloss.
Pigmented gels are a unique aspect of gels. Unlike acrylics, pigmented gels are VERY dependant upon the thickness of the gel layer prior to curing in the curling lamp. Pigments absorb UV light. That is simple to understand but it is more important to understand the meaning of that statement. If the pigment absorbs UV light, what is left to cure the gel? It is crucial (and I really mean CRUCIAL) that the pigmented gel is not applied too thickly on the fingernail. If the pigmented gel is applied too thickly, then the underside of the pigmented gel system will not cure and will remain sticky. The uncured gel will eventually lift from the rest of the enhancement and your client will return complaining of a bad job and want her fingernail to be repaired. Needless to say, this is undesirable and as such should be avoided. The procedure to avoid this error is as simple as following a very simple rule. The rule states, “if you can’t see through the pigmented gel, the UV light won’t cure the gel completely.” This means that if you can’t see through the gel when you are done applying it the UV light won’t be able to cure the thickness of the gel and you will have delamination problems between the pigmented gel and the substrate beneath it (FYI: this is bad). An exercise that I have students practice when I give a class is very simple and VERY effective. Use a standard fingernail form. Paint some pigmented gel on the form so that you can barely see the form through the gel and cure the gel in your UV lamp for the recommended time. After curing, remove the form from the lamp, cleanse the surface of the gel and peel the gel from the form. Examine the underside of the sheet of cured gel for any sticky or uncured material. If you see some uncured material, the gel was painted onto the form too thickly. If this is the case, try it again but apply the gel thinner than the first application. If you do not discover any uncured gel, then the application was of a correct thickness and further practice does not need to occur. Repeat this exercise with each pigmented gel that you want to use. Once you have the correct application thickness and you do not continue to have any thickness/curing problems, then you can rest assured that you have mastered the correct thickness application of pigmented gel systems.

I. Product Knowledge
Bonding Gels versus acrylic primers:
Product knowledge of enhancement systems is a very important aspect of becoming a nail technician. The more general knowledge that you have on how certain aspects and chemicals work, the better you will be able to do your job with less problems. How chemicals work is as important as being capable of shaping the nail to perfection.

Bonding gels are the primary aspect of adhesion of the gel enhancement to the fingernail. I have been asked on many occasions if an acrylic primer can be used under a gel. The answer to this is a resounding, “yes.” The reason why is the bonding gels typically use a specific family of acrylate (non-acidic chemical family that has at least one ethylene functional group) oligomers (a high molecular weight resin that can be polymerized) that have excellent adhesion to fingernails without the use of an acrylic acid to obtain their adhesion and these oligomers have the required ethylene functional group to allow the gel to react with them. Acrylic primers also have the ethylene functional group and as such will allow the gel to react with it.

Acrylic primers are carboxylic acids that penetrate into the keratin of the fingernail plate and have the ethylene functional group remains available above the fingernail to allow the reaction of the gel to it. This is much different than the way the gel bonding resins adhere to the fingernail. Gel bonding resins bond with the fingernail by being compatible with the fingernail while remaining on top of the fingernail, not penetrating into the fingernail. This compatibility is done by the resin and the fingernail having the same or very similar surface tension which results in the bonding resin being able to evenly coat the fingernail with the bonding resin and providing as much adhesion potential as chemically possible. Because we are not relying upon the penetration of the acrylic acid primer, fingernail preparation is crucial. It is very important to create as much surface area on the fingernail, which is done with a file. When filing the fingernail, it is helpful to use a coarse grit file (a 100 grit file) while not thinning the fingernail or removing the thickness of the fingernail. So, we advise using a coarse grit file with a VERY light touch. The use of a 100 grit file creates a wonderfully rough texture with a lot of surface area that will give the gel bonding resin plenty of adhesion and the best possibility of success for the gel enhancement to adhere. The acrylic primers penetrate into the fingernail keratin and the actual preparation of the fingernail becomes less significant because of the penetration. So when an acrylic primer is being used, a lighter grit file is all that is required. The disadvantage of using an acrylic primer is the acidic content and the odor. I prefer not to use an acrylic acid (or esterified acrylic acid) for the lone reason that I do not like to have those resins in my systems or in my manufacturing facility. If you would like to know the true health risk potential of those chemicals, look online in the World Wide Web for “acrylic acid material safety data sheets”. This search will give you the web based MSDS sheets for acrylic acid resins. You will be able to read for yourself what health effects could be a result of over exposure to these types of resins.

Enhancement Resins:
The function of all (acrylic and gel) enhancement resins is to thicken the fingernail while not destroying the natural nail. The increase in thickness is easily done but is it done well? Some resin systems use very soft and flexible resins that are not strong and flex with every movement of the fingernail while offering very little rigidity or support. Other resin systems offer extremely rigid enhancements that crack and break easily. Acrylic systems have long cornered the market of enhancements as systems that resist being easily broken and offer exceptional adhesion to the natural nail. Gels are now becoming better known for adhesion and being flexible and strong! The availability of resins and technology to the gel manufacturers is becoming more diversified and advanced to the point of being superior to acrylic technology. All of these advances come in systems that do not require the use of materials such as acrylic acids that are very odiferous and can cause nausea. The advances in technology that is available to gels is extremely helpful because it offers the nail technician choices to have an enhancement that is both flexible and hard as well as extremely abrasion resistant. These new advances are able to create gels that are tough! This new generation of gels takes the theory of gels to a new level and as such can make generous rewards to nail technicians who decide to use them. The resultant cured gel systems of this new technology have less breakage, less lifting and thinner finished products than the older acrylic systems or the more conventional gel systems.

The issue with the more traditional brittle or flexible systems is that the fingernail itself could be either flexible or brittle. While a brittle gel will work on a brittle fingernail, it will not work well on a flexible fingernail. A flexible gel will work on a flexible nail but does not offer any significant improvement to a rigid fingernail. It is important to note that each conventional system does not do well with nails that are prone to cracking or breaking. The newest gel systems from McConnell Labs offer great tear strength and hardness while remaining flexible. These new gels are perfect for all types of fingernails and because they resist breaking and tearing, they can be used for the fingernail types that are constantly cracking! If a chemist could imagine a perfect gel system (or a perfecta acrylic system) he or she would create a polymer that is both flexible and stiff, hard and strong, and all of that with superior abrasion resistance and durability! This is what we have created at McConnell Labs our nail system.

While it has become possible to create a perfect gel system, it is only genetically possible to create the perfect natural nail. The best solution for those of us who were not genetically blessed with the ideal fingernail is to not remove more of the fingernail as possible when we prepare the fingernail to accept the enhancement that we plan to place upon the nail. This means that when the fingernail is prepared to receive the enhancement that the abrasion of the fingernail should be kept to a minimum to preserve as much of the natural integrity of the fingernail as possible. The strength of the natural nail can never be replaced. The natural nail is the foundation on which the rest of the enhancement is to be created. If the foundation is weak then the enhancement will not withstand the turmoil that will beset it in everyday life. If the natural nail is left as thick and strong as possible, then the enhancement will have the best potential to survive the storm of damage from everyday life. There is a misconception that the plastic of the enhancement will replace the fingernail. This could be no farther from the truth! The enhancement is just that which it is named – an enhancement! There is no replacement for the natural nail. The natural nail provides only the potential for a successful enhancement but in itself it is no replacement for the real thing. The gel or acrylic is only in place to create an increase in the arch and / of curve of the fingernail not to replace its strength. The misnomer of “fake fingernails” could not be more of a misrepresentation of the truth. These are not fingernails that we create; they are only plastic representations of the desired effect of our work – to make the real thing a little better.