High VG e-liquid has become increasingly popular over the last few years, especially with the advancement of e-cigarette hardware. Vapers love to experience rich clouds of flavour, accompanied by the sweet aftertaste of a high glycerine vape. For many it’s not just about the smooth vape, but the whole sensory experience of opening the bottle and when the flavour aroma first hits the nose. There are so many flavours to choose from, especially the sweet confectionary tastes which we know many of you love.
Many UK manufactured and USA import high VG e-liquids are advertised as 75-80 % VG, but does ultra-high VG deliver the best possible vape? The formulation team at Totally Wicked decided to investigate.
The Chemistry bit
The first step was to prepare a series of test e-liquids with VG content of 75-80 % w/w. The series included several different popular flavours and nicotine strengths varying from 0 to 1.0 %. Before performing any fancy analytical chemistry, the simple observation was made that several of the test e-liquids had separated into two distinct layers. This was even more pronounced at low nicotine concentration (0.3 %), and worse still at zero nicotine. The flavour of the test e-liquid was terrible, as all the flavour ingredients were concentrated at the top of the bottle with no flavour at all towards the bottom! Some of the other test formulations appeared to mix with satisfactory taste throughout the bottle, but sometimes we cannot fully rely on appearance/taste to assess a formulation so we delved a little deeper.
Each sample was subject to Gas Chromatography-Mass spectrometry (GC-MS) analysis and the results were quite revealing. Despite the appearance of the e-liquid, the analysis showed a poor distribution of flavour components through-out the e-liquid. Significant quantities of flavour components concentrated towards the top of the samples, with an uneven distribution further down the sample. Most importantly, the nicotine component of the formulations was not evenly distributed, so the concentration of nicotine was higher at the top of the e-liquid than the bottom! This effect was more prominent for 80 % VG formulations, combined with certain flavour groups.
Like dissolves like!
So why is ultra-high VG quite a troublesome diluent for e-liquid formulation? Think of it this way, glycerine is a viscous liquid that is similar in chemical polarity to water. In chemistry, like solvents dissolve like solutes and this is why glycerine is readily soluble in water and attracts water molecules from the air (hygroscopic). Flavour chemical components tend to be less like water and more like oil, at least in terms of their solubility. So many flavours do not readily dissolve in glycerine and separate out to form two layers. Nicotine can aid flavour component solubility, but this effect is limited to higher strengths (1.0 %) with little benefit observed at lower strength (0.3 %). So the take home message is that many of the flavours that you enjoy are not suitable for ultra-high VG formulations (75-85 %). So how do overcome this formulation problem?
For the best high VG vape, we want to maintain the viscosity (thickness) of the juice but balance this against flavour/nicotine solubility (as discussed) and device atomiser performance. There is no point having an e-liquid that is too viscous for consistent wicking of the atomiser. So it becomes a trade-off between viscosity and the ability of the diluent to fully solubilize (mix) the flavour part and nicotine part of the e-liquid. Propylene glycol is a diluent that you are all familiar with and quite simply it’s a better diluent for solubilizing flavours. Through an extensive series of formulation experiments, utilising the techniques already described, it was determined that VG ratios between 60 and 65 % (flavour and nicotine dependent) were optimal for a high VG vape. The optimal PG ratio was approx. 35 %, again dependent on flavour and nicotine formulation. All the indicative parameters for the best VG juice were satisfied including the all-important vape experience for the end user.
So the take home message is this, sometimes less is more and this certainly applies to finding the perfect balance for a high VG juice. The best e-liquid formulations are now being developed with a fine balance of creativity and making use of the analytical tools available to the modern formulation chemist.
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