Keeping viscosity in mind?

[Alien Traveler]

I have started a thread on evaporation process and cordially invite everybody to kick my .....

http://www.e-cigarette-forum.com/fo...37-how-works-coils-temperature-juice-etc.html

 

[Alien Traveler]

My concern in DIY was how well my VG juices wicked and still vaped well. Flavors (mostly PG with often other small organics) tend to thin VG, and so does water, and I found that if %flavor + %water = ~22%, the juice would wick well for most of my attys. When I was using ethanol, it was %flavor + %ethanol = ~17%. Relating this to your excellent calculations, these juices were still much thicker than pure PG, but they were thin enough to work very well in my PVs.

I think it is because ethanol may help in increasing wettability. Wettability could be as important as viscosity.

 

[scutterflux]

Not a problem at all. I live in a peer reviewed world, ...

But WHY water is less viscous than ethanol is a mystery to me.

Hey Kurt, if you know the molar volume of VG my calculations could be off. I made an assumption that the molar volumes where similar in my calc, and I think that online calculator I used makes the same assumption as it asks for no molar volume ratio, just ratio. Perhaps because that calculator was found on a site having to do with oils??? I'm assuming then maybe those long carbon chains maybe have a similar molar volume??? Isn't the VG molecule quite a bit larger than a water?

Anyway do you think perhaps the O's are fighting for each others H's in Alcohol, making them stickier (viscous) but ...... off and smaller so they boil quicker?

 

[Kurt]

Hey Kurt, if you know the molar volume of VG my calculations could be off. I made an assumption that the molar volumes where similar in my calc, and I think that online calculator I used makes the same assumption as it asks for no molar volume ratio, just ratio. Perhaps because that calculator was found on a site having to do with oils??? I'm assuming then maybe those long carbon chains maybe have a similar molar volume??? Isn't the VG molecule quite a bit larger than a water?

Anyway do you think perhaps the O's are fighting for each others H's in Alcohol, making them stickier (viscous) but ...... off and smaller so they boil quicker?

Good point, and you may be correct. Mol% for VG/water are not the same as volume%. 90% VG: 10% water by volume I found was about 67%VG:33% water in mole%. Would this change your numbers?

@alien Traveler: this is a most excellent comment! In my world this would be referred to as capillary action, an adhesion force. I am not an expert in this, but it seems logical that if you have a highly H-bonded liquid, like VG, breaking those intermolecular interactions would have those molecule more susceptible to H-bonding with the silica or cotton, both of which adhere to a solvent by H-bonding. So in some way the lowering of viscosity is perhaps just a byproduct of increasing capillary forces (wicking).

 

[Kurt]

Hey Kurt, if you know the molar volume of VG my calculations could be off. I made an assumption that the molar volumes where similar in my calc, and I think that online calculator I used makes the same assumption as it asks for no molar volume ratio, just ratio. Perhaps because that calculator was found on a site having to do with oils??? I'm assuming then maybe those long carbon chains maybe have a similar molar volume??? Isn't the VG molecule quite a bit larger than a water?

Anyway do you think perhaps the O's are fighting for each others H's in Alcohol, making them stickier (viscous) but ...... off and smaller so they boil quicker?

I reread your question and maybe you were not referring to mole%. Yes, VG is ~6x as large as water, at least. If we take the density as 1.26 g/mL, and a MW of 92.0 g/mol, the molar volume is 13.7 mol/L. Water is 55.6 mol/L. Does this change things?

 

[Kurt]

I guess maybe I should have taken the reciprocal: VG is 0.0730 L/mol, water is 0.018 L/mol.

 

[Alien Traveler]

Good point, and you may be correct. Mol% for VG/water are not the same as volume%. 90% VG: 10% water by volume I found was about 67%VG:33% water in mole%. Would this change your numbers?

@Alien Traveler: this is a most excellent comment! In my world this would be referred to as capillary action, an adhesion force. I am not an expert in this, but it seems logical that if you have a highly H-bonded liquid, like VG, breaking those intermolecular interactions would have those molecule more susceptible to H-bonding with the silica or cotton, both of which adhere to a solvent by H-bonding. So in some way the lowering of viscosity is perhaps just a byproduct of increasing capillary forces (wicking).

I believe amplitude of capillary action depends on combination of wettability and surface tension, and its speed on viscosity as well. But I am not an expert also.

 

[scutterflux]

I reread your question and maybe you were not referring to mole%. Yes, VG is ~6x as large as water, at least. If we take the density as 1.26 g/mL, and a MW of 92.0 g/mol, the molar volume is 13.7 mol/L. Water is 55.6 mol/L. Does this change things?

I was mistaken, it was molar density I needed to calculate a weight fraction and preliminary hacking of numbers shows it seems to make a substantial difference when used with a "better" formula. I found the details I was looking for and I'm going to hammer out a matlab program tonight and I'll get back to you.

We are now looking at approx. around a .70 VG to .30 water now to equal PG... I think, we'll see.

It's really surprising that the calculator I posted earlier is off by so much, it appears to be specifically designed for mixing of their industrial oils and not able to compensate for the difference, I'll attempt to reduce the error. I see the problem is that the formula's used was probably the same one I used and upon further research into viscosity it can be quite inaccurate when calculating from viscosity and the better method is to calculate a Viscosity Blending Index first.

Also briefly looking at the density of OH looks like it will thin substantially so there's a good chance you were right all along.

 

[scutterflux]

OK, I hope I've got it this time.

Using the Refutas equation and Matlab:

Code:
%viscosity entered in cp and corrected to centistokes
H2O =0.89/1;
OH =1.095/.78;
PG = 42/.965;
VG = 950/1.26;
%enter the components in the mixture to vA,vB etc
vA=H2O;
vB=VG;
%vC=
%percentages of components in mixture
wA=.99;
wB=.01;
%wC=
%Calc the Viscosity Blending Index
VBIA = 14.534 * log(log(vA + 0.8)) + 10.975;
VBIB = 14.534 * log(log(vB + 0.8)) + 10.975;
%VBIC = 14.534 * log(log(vC + 0.8)) + 10.975;
%Calc the blend total
VBIblend = (wA * VBIA) + (wB * VBIB); %+(wC * VBIC)...
%Calc for viscosity in centistokes
viscosity = (exp(exp((VBIblend - 10.975) / 14.534))) - 0.8;

With this method it is surely more accurate...
I get:
22% water in VG = PG
26% Ethanol in VG = PG

So the suggestions I made earlier about PG to water at 10 to 4 are really more like 10 to 2 water and 10 to 2.5 Alcohol.

I will go back and correct that first post.

If someone has the tools to measure actual viscosity it would be very nice to see actual values as there could be more molecular interactions than are accounted for.

 

[scutterflux]

Is there a mod that can let me edit my first post???

Please.

 

[Kurt]

You can have a mod allow editing if you like. I personally prefer it when people see I have made a mistake and have corrected it down the line. Up to you, but none of this is at all straight forward, and I for one really appreciate your diligence in helping get to the real answers. Science is not linear!

So I was a bit low in amount of ethanol, if all we are thinking about is actual viscosity. The BP of a 20+% ethanol/VG solution is probably much lower than PG, and of course this also very important in vaping. And it is hard to know the surface tension/capillary force compared to PG, and this is also important. And it is these properties that I am having fresh thoughts about, and had not really considered a lot.

In other words, lowering viscosity is just one factor, I think, but given the solvents used (all hydroxylated) is a fairly good indicator. But if thick VG were to have very good capillary action through the wick to feed the coil well, then we would not worry about viscosity. But it often does not, so we need to thin it and reduce its surface tension with either water or ethanol (if we do not like PG). Maybe it is ultimately not viscosity matching with PG that we are after, maybe it is matching, or at least decreasing, surface tension. As well as lowering boiling point, which should go hand in hand with lowering surface tension. And it would make sense that if surface tension is an important factor, ethanol would have a stronger effect than water, and thus you need less.

This has been a really terrific conversation, including the misconceptions, corrections, recorrections, etc. This is what science is all about!

 

[retired1]

Is there a mod that can let me edit my first post???

Please.

Sorry, no. But if you report it with the edits you have in mind, one of the staff will get to it. You can also just post the correction in the thread.

 

[scutterflux]

it is hard to know the surface tension/capillary force compared to PG, and this is also important. And it is these properties that I am having fresh thoughts about, and had not really considered a lot.

Yes also wicking ability, the materials of the wick matter too. I did a quick and dirty experiment, silica, hemp, cotton cord, twisted cotton ball. the first three of equal diameter but the twisted cotton ball of greater diameter. I set them up in a race to wick VG and see who would wick the fastest and highest. Silica and hemp both appeared to be equal up until about 3-4cm when the hemp kept at the same rate and clearly surpassed the silica wick. The cotton was nearly dead in the water compared to these two only wicking 1-2 cm in the allotted time. However I still prefer cotton ball for my builds.

Maybe later I will try to look farther into capillary action of our solutions but I'm going to take a break for now.

 

[scutterflux]

Sorry, no. But if you report it with the edits you have in mind, one of the staff will get to it. You can also just post the correction in the thread.

No problem, I was thinking It could be nice for a quick reference and would save the layman from trying to sort out what's going on. Maybe another time.

But to simplify it looks like the PG to Water ratio is 10:2, not 10:4 as I had mentioned in the first post.