Monday, September 7, 2015

Gel Nails Chemistry

Light-curing gels have been around for many years (since the 1980’s), but have recently surged in popularity. Acrylic (“Liquid and Powder” or L&P in the UK) and Gel Nails seem totally different and unrelated, but nothing could be further from the truth. Gels are often sold as being ‘not acrylic’, but in fact are based on both the methacrylates and the acrylates family. The difference is twofold – one, gels are not made of monomers and polymers as L&P are; rather, they are made of oligomers, which are single chains that are several thousand monomers long. They are basically in between a monomer and a polymer in terms of molecule length, which is why they are in a “gel” form.
The other main difference between a gel and an L&P enhancement is the type of initiator that is used. Gel nails use a photo initiator which starts the polymerization process when UV light “activates” them. (LED is on the ultraviolet light spectrum, therefore if I reference UV I am also referring to LED lamps and wavelengths.) Photoinitiators are light sensitive and decompose into free radicals to start the polymerization process. Photoinitiators absorb UV light and convert it into the energy needed to drive the polymerization (curing) process .The thicker the gel is applied, the more photoinitiators there are present in that layer and the higher the temperature of the exothermic reaction (heat spike). Photoinitiators are most effective at a specific bandwidth which means that the same chemistry that photo-cures in UV may not work with LED. Different photoinitiators may be needed in a gel to cure in a UV lamp versus an LED lamp.
One major cause of service breakdown with any gel system is that gel has not sufficiently cured. A very common cause of this problem can be the use of an incorrect lamp for a particular system. Not all lamps are created equal and some give off more UV energy than others. Wattage is not a sufficient indicator of the amount of UV energy given off. Transparent and semi-transparent gels will typically cure completely in 2 – 3 minutes at any thickness. Super bright whites and highly pigmented deep rich colors contain more Titanium Dioxide (which makes them opaque). It’s harder for UV energy from a lamp to pass completely through these gels, especially if the gel is applied too thick. The whiter a gel is, or the more intense a color is, the greater the possibility that the UV energy is blocked. What does this mean? Just be cognizant of how you are applying white and heavily-pigmented gels. Rather than applying them really thick, try doing multiple layers and curing in between. This will ensure a complete cure and prevent overexposure and service breakdown.
Bulb condition is vital to the success of gel enhancements. UV lamps become ineffective many months before they burn out. After about 6 months of normal use, a bulb has less than half its original UV energy. UV bulbs should be changed at least twice per year even if they look fine. If the product seems to set slower than normal, change the bulbs immediately. Clean the bulbs whenever needed or at least once per week. LED Bulbs do not need to be changed according to current recommendations, but should still be kept clean.