The density of liquids and possible volume contration
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Thread: The density of liquids and possible volume contration

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    Default The density of liquids and possible volume contration

    Yesterday I measured the density of a 36 mg PG liquid known to be only nic and PG to be 1.128 g/mL. The density of pure nicotine liquid is 1.009 g/mL, and the density of pure PG is 1.036 g/mL. Thus if there is no change in volumes upon forming a solution, the final liquid density should be somewhere between these two densities of the pure substances.

    What this implies is if a 250 mL 36 mg liquid is made from .036*250/1.009 = 8.92 mL pure nicotine, and the volume is brought to 250 mL with the remaining 241.08 mL, when the solution is finished forming, its volume will only be 223 mL, and the actual nic concentration will be about 40 mg/mL, not 36 mg/mL.

    I do not work with pure nicotine, and have not made any liquids from PG or VG and pure nic myself, so I cannot verify that the solution actually did contract. I only measured the density of a known liquid sent to me by a vendor. That liquid titrated to 43.5 mg, so perhaps this is was much of the issue, along with the usual error associated with any volume dispenser. Not saying who the vendor is, since there have been no complaints, he just wanted me to test his. He makes liquids individually per bottle, using a volumetric syringe to deliver the pure nic to the bottle, dilute it up to the level for that bottle with PG, and shakes it up for a while.

    Is such a contraction known with these liquids? Something is increasing the density, and a post diluting contraction is the only thing I can come up with. Such an effect would not surprise me, since both nic and PG are hydrogen bonding and a solution may disrupt some of them. For a similar reason a volume of solid ice will contract when it melts, the result of some of the H-bonds breaking in the melt.
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    ECF Guru ECF Veteran 36tinybells's Avatar
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    Have you tried a vg + nic solution yet? Might be interesting to have a comparison result. And what about just the vg and the pg? I am no chemist- but this is all very interesting.
    Last edited by 36tinybells; 12-04-2011 at 10:33 PM.

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    I did try a VG-nic liquid, and while I got a similar result, I don't know for sure what the composition is. Many vendors add a little water to their VG-nics. I did this originally to see if by measuring the volume and mass of some quantity of liquid I could use the densities of pure PG and nic to algebraically work back to the nic content. If there was no total-liquid volume change, I would have been able to do it, but with a density higher than either component, no go.

    PG and VG have known densities at room temp: 1.036 and 1.261 g/mL, respectively.

    The algebra is two equations, two unknowns:

    Let mnic = mass of nic, mPG = mass of PG, Vnic = volume of nic, VPG = volume of PG, dnic = density of nic, dPG = density of PG.

    mnic + mPG = mT, with mT = total mass

    Vnic + VPG = VT, with VT = total volume

    If we sub mnic = Vnic*dnic, and mPG = VPG*dPG, we can get to an expression for mnic:

    mnic = (mT - VT*dPG)/(1 - dPG/dnic)

    My VT = 12.00 mL
    My mT = 13.544 g

    This gives a negative number for mnic. The expression assumes that the total volume of the liquid will be the sum of the volume of the nic and the volume of the PG. And this clearly is not the case. I think my algebra is correct, but logically, the density of the liquid cannot exceed that of either component...unless it shrinks when it is fully formed as a solution, which does happen with some water-based solutions.
    Last edited by Kurt; 12-05-2011 at 01:10 AM.
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    Could this additional density be caused by PG's tendency to attract moisture (humidity) or does that just increase the volume?
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    For the practical purpose of making liquids, this is the difference between molarity and molality. For mixers--and authors of mixing software and guidelines--it's whether or not to measure separately or "volumetrically", which is to add the solute (nicotine) and then fill to the mark with solution (PG). There seems to be a practical lesson for all of us in your observations.

    But you asked something far more interesting. I'm no chemist--just a guy that does a bit of etching and the tad of chemistry needed to balance the bath--so I don't pretend to understand or be able to tell which factors are important. Also, everything I could find was about the chemistry on nicotine in water or with the more usual reactants, such as metal salts, acids, etc.

    At least one factor is that nicotine is amphiphilic (obviously in water), and will form micelles at higher concentrations. In Chemistry 001 terms, it means they can take up less space when combined. In Chemistry 101 terms: At low concentration, the hydrophyllic ends will snuggle close to the water, but at higher concentrations there won't be enough water, and the nicotine will bunch together, staying away from the water, and take up more or less the same space it requires as pure nicotine. But if the nicotine molecules are snuggled up with the water (in low concentration), they're packed in pretty neatly in the space the water doesn't need, and the solution takes up less space, making the solution denser at low concentration. That corresponds to what you observe.

    There do seem to be a lot of other complicated factors, but they're way over my head, and I can't tell if any matter. Certainly not in an hour. One that does matter is that there's a low point along the concentration/density curve, which seems to mean that below that level of concentration, the density will begin to decrease again.

    For what little the terms amphiphilic and micelle are worth, and whether or not it even works in PG... Well, maybe it does and maybe it doesn't, but if it does, it supports your observation. It certainly fits with your ideas of H bonds. We obviously need a real chemist here.

    The one thing that puzzles me is that the curves only show about 0.7% of a change. Maybe I don't understand the meaning of the graph. For what it's worth, the math & discussion gives 9cc/mole. (I read that at the end after my eyes recovered.) Maybe that will make more sense to you than to me.

    There was also stuff online about how to calculate the concentration of these kinds of solutions, but it was way beyond me, between theory, math, and technique, but there was also mention about something not quite stable about nicotine's density in water, so there seemed to be a lot of extra stuff to consider. Hopefully, there's other ways. Perhaps optical deflection? Or just do the titration. Do enough of those and you could make a density graph for future quick reference. (But what about added water?)

    reference 1
    reference 2
    Last edited by SiBurning; 12-05-2011 at 09:37 AM. Reason: Couple mistakes, additional information & thoughts

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    Thanks for the links, SiBurning. Generally hydroxylic compounds will increase their density as H-bonds are broken. Witness water when it melts: its density as liquid is less than that of ice. Actually I lectured on that today in my general chem course!

    But for this, regardless of the theory behind the why, the fact remains that this seems to occur, at least in PG-nic solutions. The vendor whose liquid I did the measurements on is now trying to do some experiments to see if he can actually see this contraction of the solution. I don't know how long it takes to manifest, but given the higher viscosity of PG compared to water, it might take some time.

    Yes, these liquids we take for granted now do evidently have some properties that make them a bit unpredictable. Your thoughts about molality vs molarity are correct, but the final concentration we use is closer to molarity (moles of soluter per L of solution) than molality (moles of solute per kg of solvent).

    I would make a plot of density vs nic conc, but I would need a bunch of verified liquids, and I'm not sure what it will actually do for us. My point here was that it seems there may be a contraction of the liquid volume after the solution process is complete at the molecular scale. So to alleviate this, more PG or VG should be added to make sure the total volume is what it is supposed to be. How long it takes for this contraction to occur is not known right now, but the density shows it can occur, and may affect the nic concentration by about 10% (maybe more, maybe less, depending on the liquid).

    Perhaps other vendors that mix from pure nic can make notes of this. I think if the volume is adjusted to maintain correct level, this problem will be largely solved.
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    Are any of this vendors using PEG 400 for their nic solutions?
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    Quote Originally Posted by Kurt View Post
    My point here was that it seems there may be a contraction of the liquid volume after the solution process is complete at the molecular scale. So to alleviate this, more PG or VG should be added to make sure the total volume is what it is supposed to be. How long it takes for this contraction to occur is not known right now, but the density shows it can occur, and may affect the nic concentration by about 10% (maybe more, maybe less, depending on the liquid).
    I missed that point entirely.

    Thanks for taking the time. It clarifies what a DIY liquid maker can expect, and points to some things to play with. Naturally, it's kind of secondary-level working with 10% nicotine in VG, with some unknown water content after sitting around. But I don't need much excuse to learn something new or brush up on technique.

    Looking forward to reading some more fundamental results.

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    Quote Originally Posted by AzPlumber View Post
    Are any of this vendors using PEG 400 for their nic solutions?
    None that I am working with, or at least the liquids I am analyzing. I just want to figure out PG-nic right now. Then maybe VG-nic. Those are coming up too dense too, but I don't have verified compositions yet. Some add water to them.
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    Very few use PEG-400 for their nic bases. In fact, the only one I have personally come across that does is Decadent Vapors
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