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Author Topic: Increasing surface tension with liquid density lower than water  (Read 7546 times)

Offline Da9L

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First of all.. Im very new to this, and second i hope you can understand my english!

As a hobby, i work with lava lamps, and mess with their liquids to change flow and other stuff.. This is to fix some lamps that looks very bad when i get them.

But okay.. The basic way a lava lamp works is that the wax (the lava) is heated up by the bulb, and therefore it liquidifies. It then changes density to something that is less dense than water and therefore rises to the top. When it cools down, the density increases, and makes it fall back down. Thats very basic but should be enough.. :)

I then have this one lamp where the density of the wax is so light that it will allways be on top of the lamp when liquid.. And this makes it look bad.

I have therefore used 1-propanol to change the density of the water in the lamp, to become less dense than the wax when its liquidified.. This works and the flow is good now, but theres an issue.

Normally the waxes density is much higher than in this lamp, and therefore i normally have to increase the density of the water in the lamp. At first i used a simple salt solution to do this, but i experienced that the wax would become "bubbly" and found out that this was because the salt decreases the surface tension of the water.. So instead of using salt i began using Glycerin to increase the waters density, which worked for me.. no more bubbly wax.

The problem is that when i work with this particular lamp i dont know anything i can add that would increase the surface tension, and remove the bubbles, without also increasing the waters density, and therefore make all the wax go back to the top as soon as its liquidified. So my main question is this

Does there exist any kind of liquid i can add to my solution that has a density which is lower than water and yet increases the surface tension?

Im sorry if that is a very dumb question.. I have no experience in chemistry at all, so this is a shot in the dark!

Thanks !


 

Offline jmplayer22

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 I've heard of Tetrachloroethylene specifically being used to increase the density of "wax" or "goo" inside of lava lamps (especially homemade).  I personally have seen success using Tetrachloroethylene, but came across your post while looking for alternative, more "healthy" solution.  It's not really something you want to breath in; however, it's sold in chlorinated brake cleaner (I've only been able to find "Brake Kleen").  Not sure if it's even so dangerous to require ID when purchasing, but even so...it's still sold in stores, so while it's probably not EXTREMELY dangerous, take precautions and use outside if possible.

Here's a link to a great site that might be helpful to you working with lava lamps:
newbielink:http://www.oozinggoo.com [nonactive]
 

Offline William McCormick

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First of all.. Im very new to this, and second i hope you can understand my english!

As a hobby, i work with lava lamps, and mess with their liquids to change flow and other stuff.. This is to fix some lamps that looks very bad when i get them.

But okay.. The basic way a lava lamp works is that the wax (the lava) is heated up by the bulb, and therefore it liquidifies. It then changes density to something that is less dense than water and therefore rises to the top. When it cools down, the density increases, and makes it fall back down. Thats very basic but should be enough.. :)

I then have this one lamp where the density of the wax is so light that it will allways be on top of the lamp when liquid.. And this makes it look bad.

I have therefore used 1-propanol to change the density of the water in the lamp, to become less dense than the wax when its liquidified.. This works and the flow is good now, but theres an issue.

Normally the waxes density is much higher than in this lamp, and therefore i normally have to increase the density of the water in the lamp. At first i used a simple salt solution to do this, but i experienced that the wax would become "bubbly" and found out that this was because the salt decreases the surface tension of the water.. So instead of using salt i began using Glycerin to increase the waters density, which worked for me.. no more bubbly wax.

The problem is that when i work with this particular lamp i dont know anything i can add that would increase the surface tension, and remove the bubbles, without also increasing the waters density, and therefore make all the wax go back to the top as soon as its liquidified. So my main question is this

Does there exist any kind of liquid i can add to my solution that has a density which is lower than water and yet increases the surface tension?

Im sorry if that is a very dumb question.. I have no experience in chemistry at all, so this is a shot in the dark!

Thanks !

Bees wax might mix with a little solvent and water. I think they use that in the cosmetic industry. I just don't know if the bees wax will mix with your colored wax.

                      Sincerely,

                            William McCormick
 

Offline damocles

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What you really need for a lava lamp is a liquid or liquid mixture that:
(1) Has very low solubility in water
(2) Has a density close to that of water
(2) Has a coefficient of expansion greater than that of water
(3) Has surface tension properties such that it will not spread on top of water (although this last requirement may not be important if there is no air bubble at the top of the lamp).

You also need a dye or colouring material that will dissolve in the oil phase but has very low solubility in water, and materials that are free of any sort of detergent or other surfactant material.
In terms of this last requirement, it is probably wise to avoid adding anything at all to the water, and to do all of your mixing in the materials involved in the oil phase.

So the best strategy is to identify and use -- (1) An water-insoluble oil that is less dense than water; (2) An oil, wax, or organic solid, similarly insoluble in water, that will dissolve in the oil to make a mixture that is just fractionally more dense than water at about 30C. (3) A colouring material that will dissolve in the oil phase but not in water.

You mix (1) and (2), put in just a little of (3) to achieve the colour you want, add the oil to the lamp, and fill with clean boiled water, filling the lamp to the brim.
In operation, the lamp will heat the oil from below, making it less dense than the water, and it will rise. If the oil/water phase density difference is small and the interfacial tension is large, the oil will rise in large dollops in convection currents when it gets hot enough that its density is lower than that of the overlying water phase. Small dollops or breakup of dollops into tiny drops means that you have low interfacial tension, that is, surfactant/detergent contamination. Note that many (most?) dyes have some surfactant properties, so the colouring matter needs to be chosen with great care.

Chlorinated compounds were a common and convenient choice for component (2). There are good safety and environmental reasons for avoiding them, but there are still some that are readily available, and you will not be handling them often or using much. There are not many oils nor readily available oil-miscible compounds that can produce a phase more dense than water. Mixing things with water to make it less dense than pure water is problematic because most such substances have surfactant action and/or significant oil solubility.
 

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