How much emulsifier?

[tim.tdj]

Hi Everyone

Lets say there is a container which contains 50g of oil floating on top of 50g of water. What is the minimum amount of washing-up liquid needed in order to fully and permanently emulsify the oil and water?

Thank you very much.

Kind regards

Tim

[StringJunky]

I think that's a "How long is a piece of string?" question. The ingredients and concentration will vary wildly. I think you will have to find out experimentally by adding drops at a time.

[DrP]

4 minutes ago, tim.tdj said:

What is the minimum amount of washing-up liquid needed in order to fully and permanently emulsify the oil and water?

I think it would depend on the surfactant used in the washing up liquid, it's concentration and it's critical micelle concentration or something like that.

I wouls guess at somewhere between 0.5 and 2%...  but that is a total guess

 

*Plays 'Blue Danube music for synchronised posting*

Edited November 21, 2018 by DrP

[tim.tdj]

35 minutes ago, StringJunky said:

I think that's a "How long is a piece of string?" question. The ingredients and concentration will vary wildly. I think you will have to find out experimentally by adding drops at a time.

 

34 minutes ago, DrP said:

I think it would depend on the surfactant used in the washing up liquid, it's concentration and it's critical micelle concentration or something like that.

I wouls guess at somewhere between 0.5 and 2%...  but that is a total guess

 

*Plays 'Blue Danube music for synchronised posting*

Hi StringJunky and DrP.

Thank you both very much for your replies.

To be honest, I was only after a rough answer which I think you have given.

It seems to me that not very much emulsifier is needed compared to the main substances being mixed together. If only a small number of oil molecules in a mixture are bonded by a small number of emulsifier molecules to a small number of water molecules in the mixture, do any of you know how this can help the non-bonded oil and water molecules remain mixed together?

[DrP]

9 hours ago, tim.tdj said:

It seems to me that not very much emulsifier is needed compared to the main substances being mixed together. If only a small number of oil molecules in a mixture are bonded by a small number of emulsifier molecules to a small number of water molecules in the mixture, do any of you know how this can help the non-bonded oil and water molecules remain mixed together?

The amount of surfactant molecules needed will also depend upon the droplet size of the oil.  The mixture isn't like a solution with molecules of oil in the water...  it will be droplets of oil suspended in the water. The smaller the particle size then the larger the total surface area of the droplets and the more surfactant needed to keep the suspension stable.

[tim.tdj]

8 hours ago, DrP said:

The amount of surfactant molecules needed will also depend upon the droplet size of the oil.  The mixture isn't like a solution with molecules of oil in the water...  it will be droplets of oil suspended in the water. The smaller the particle size then the larger the total surface area of the droplets and the more surfactant needed to keep the suspension stable.

Hi DrP

Thank you very much for your reply.

Does this mean that the more surfactant you add, the smaller will be the average droplet size? (assuming you shake the container after adding the surfactant)

Also, am I correct that if there is just a single droplet of oil in a container of water and the oil droplet is surrounded by a layer of surfactant, the surfactant will not stop the oil droplet rising to the surface of the water?

[DrP]

47 minutes ago, tim.tdj said:

Does this mean that the more surfactant you add, the smaller will be the average droplet size? (assuming you shake the container after adding the surfactant)

I think the particle size will depend more on the level of aggitation when stirring the system. The surfactant then will stablize the droplets in suspension....  you will need more to stableise the smaller drop size I think, but the act of putting in the extra surfactant wont make the droplets smaller to begin with. 

 

50 minutes ago, tim.tdj said:

Also, am I correct that if there is just a single droplet of oil in a container of water and the oil droplet is surrounded by a layer of surfactant, the surfactant will not stop the oil droplet rising to the surface of the water?

If the oil is less dense than the water then it will float, yes. 

[tim.tdj]

24 minutes ago, DrP said:

I think the particle size will depend more on the level of aggitation when stirring the system. The surfactant then will stablize the droplets in suspension....  you will need more to stableise the smaller drop size I think, but the act of putting in the extra surfactant wont make the droplets smaller to begin with. 

If the oil is less dense than the water then it will float, yes. 

Hi DrP

Thank you very much for your reply.

I am guessing that the following question is a very difficult one to answer so I will fully understand if you can't answer it. Do you have any idea how to calculate the minimum amount of surfactant needed so that if given a large amount of initial agitation, the oil:water ratio at the bottom of the container will stably remain the same as at the top of the container? (Putting this another way, so there is no separation whatsoever.)

Edited November 22, 2018 by tim.tdj

[DrP]

1 minute ago, tim.tdj said:

how to calculate the minimum amount of surfactant needed so that if given a large amount of initial agitation, the oil:water ratio at the bottom of the container will stably remain the same as at the top of the container?

As different surfactants vary in their effectiveness you would have to have a fudge factor in the equation for the specific system I would think. It will also depend on what is being suspended. You will need to do some tests to find the optimum concentration you require for stabilization of your suspension experimentally like String Junky suggested I would think  -  sorry.  Maybe someone else will have a better idea but I doubt it....  if there are equations (which there probably are somewhere) then they would be for ideal or know systems... I think you will have to try what String suggested and try a range of tests with incrimental increases in the surfactant amount untill you find a level where the suspension is stabilised. 

I think you will need to trial ammounts you need for your system...  maybe start a half a percent and increase in half percent intervals up to a few percent....  see which best stabilizes you emulsion/suspension and 'zoom in' to that concentration and repeat the tst around that concentration with 0.1 % variations above and below your best res result from the first test   -  something like that.  I searched around to see if I could find anything better and it seems that we are on the right track...  there is a discussion about selecting surfactant conc below I found and it suggests similar things to what we have discussed here.  I hope this helps.

https://www.researchgate.net/post/What_should_be_the_amount_of_surfactant_required_for_emulsion_polymerization

https://www.google.co.uk/search?source=hp&ei=jp72W43qF8zfgAaQ4IvIBw&q=calculating+surfactant+requirements+for+suspension&btnK=Google+Search&oq=calculating+surfactant+requirements+for+suspension&gs_l=psy-ab.3...1725.19740..20925...0.0..0.226.4057.42j7j1......0....1..gws-wiz.....0..0j0i131j0i10j0i13j33i160j33i21.W8D1Qg9yIHU

 

 

 

[tim.tdj]

16 minutes ago, DrP said:

As different surfactants vary in their effectiveness you would have to have a fudge factor in the equation for the specific system I would think. It will also depend on what is being suspended. You will need to do some tests to find the optimum concentration you require for stabilization of your suspension experimentally like String Junky suggested I would think  -  sorry.  Maybe someone else will have a better idea but I doubt it....  if there are equations (which there probably are somewhere) then they would be for ideal or know systems... I think you will have to try what String suggested and try a range of tests with incrimental increases in the surfactant amount untill you find a level where the suspension is stabilised. 

I think you will need to trial ammounts you need for your system...  maybe start a half a percent and increase in half percent intervals up to a few percent....  see which best stabilizes you emulsion/suspension and 'zoom in' to that concentration and repeat the tst around that concentration with 0.1 % variations above and below your best res result from the first test   -  something like that.  I searched around to see if I could find anything better and it seems that we are on the right track...  there is a discussion about selecting surfactant conc below I found and it suggests similar things to what we have discussed here.  I hope this helps.

https://www.researchgate.net/post/What_should_be_the_amount_of_surfactant_required_for_emulsion_polymerization

https://www.google.co.uk/search?source=hp&ei=jp72W43qF8zfgAaQ4IvIBw&q=calculating+surfactant+requirements+for+suspension&btnK=Google+Search&oq=calculating+surfactant+requirements+for+suspension&gs_l=psy-ab.3...1725.19740..20925...0.0..0.226.4057.42j7j1......0....1..gws-wiz.....0..0j0i131j0i10j0i13j33i160j33i21.W8D1Qg9yIHU

 

 

 

Hi DrP

Thank you very much indeed for all your help.

Kind regards

Tim