UV or not UV, that is the question?!

I am in love with UV gel nail varnishes at the minute. They are hard wearing and long lasting. But the real question I want to know the answer to is how do they work? 

Pink Shellac nails

Unlike regular nail varnish, Shellac is a gel polish that is advertised as lasting up to fourteen days. In my experience it will last a lot longer, however after two weeks your nails have grown out and they don't look quite as nice. My nails have been tried and tested a lot a bar tender at Wetherspoons. Continuously wet, in and out of water. Never mind the battering they get pulling pints and putting glasses away. Shellac survives where less nail varnishes do not and after a week of long shifts and the busiest weekend Whitehaven's spoons has ever seen, my nails are still intact.

UV gel kit

My sister and I recently decided to invest in a do it yourself UV gel kit. After a couple of pricey trips to the salon we  thought our hand's were steady enough to try this ourselves. Being the thrifty students that we are we shopped around, so many nights trolling amazon, until we found a set that looked half way decent. It came with all the paraphernalia: UV lamp, base coat, top coat, nail prep solution, remover and some fancy lint free wipes.

Having had it done a couple of times, we knew the drill when it came to applying the polishes. Prep, base coat, UV, colour, UV, top coat, UV, wipe.

One thing I noticed upon inspection of bottles was that each coat contained a compound called urethane acrylate oligomer. An oligomer is a short chain of monomers, generally fewer than five monomers. Unlike a polymer where the number of monomer units is potentially infinite.

                


Another component of the polish that is important in the curing of the gel varnish is benzoyl peroxide. This chemical is responsible for starting the polymerization reaction, which proceeds via radical polymerization. When exposed to UV radiation the benzoyl peroxide molecules undergo homolytic cleavage to give two radicals. These decompose, releasing carbon dioxide and the remaining phenyl radical goes on the initiate polymerization; attacking the double bond of the acrylate. Polymerization is terminated when two carbon centered radicals combine.

The shellac polish is a lot thicker when compared to normal nail polish and when we think about the fact that we are starting with small oligomer chains as opposed to monomers, it makes sense. A thinner polish made from monomers would take a lot longer to cure under the UV and would be less efficient at creating the polymer. So the oligomer gel is a happy medium between inefficient liquid monomers and the desired solid polymer.

After you have applied all of your layer, you have achieved the desired colour and you have completed the last UV curing, there is a wipe with the first solution. This solution contains isopropanol which removes the sticky top layer of uncured gel and finishes the look.

After a few weeks growth comes time to remove the polish. This is the fun part. You get to wrap your fingers up in acetone soaked cotton wool pads, topped of with a layer of tin foil. Before leaving your turkey fingers to stew for about ten minutes. After which time the shellac layers begin to flake off the nail. Because the gel polish is a lot thicker, a stronger remover is required. Our kit came with a special remover, with a high acetone concentration ( I managed to melt off my acrylic nails...) compared to the stuff sold in high street shops.





So to recap, we have a UV initiated, radical polymerization reaction that makes the solid elastomer coating that gives shellac nail polish it's hardiness and longevity. That's a lot of chemistry in one tiny bottle...