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I'm doing an engineering experiment soon and would like to be able to quickly dye water. The water is still (i.e. not moving) and I would prefer not to physically disturb the water as best I can.

What techniques could I employ to quickly diffuse a dye through water? I was thinking that electrophoresis could be a possibility. If so, what dyes (or what could I add to a dye) to help speed up the process.

Thanks in advance.

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    $\begingroup$ Do you have some way of suppressing convection? How do you intend to prevent "disturbing the water"? $\endgroup$ – Buck Thorn Mar 22 at 12:47
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    $\begingroup$ By definition diffusion is a passive process. You have to describe in detail what kind of distribution you want in the end. Electrophoresis will not give a uniform (homogeneous) distribution and can cause all sorts of convective currents due to Joule heating. You'll need to describe the experimental setup in more detail. $\endgroup$ – Buck Thorn Mar 22 at 12:51
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    $\begingroup$ "Not moving" Molecules are moving. That is why diffusion takes place. If the water is not moving then certainly the water molecules can't move out of the way to allow for diffusion of a solute. $\endgroup$ – Zhe Mar 22 at 13:37
  • $\begingroup$ @NightWriter we have a slushy mixture of water and ice. I want to be able to distinguish between the two later. The idea is to quickly dye the water and the freeze the entire mixture. I would like to keep the shape of the composition. That is what I mean by not "disturbing the water". $\endgroup$ – rxc370 Mar 22 at 15:33
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    $\begingroup$ I see, I suppose if you are concerned about breaking fragile crystal structures then stirring is not what you want. Also, adding a dye in significant concentration will alter freezing point possibly or be incorporated as inclusion impurities into the crystals etc etc, so you don't want to add it before hand. Electrophoresis might significantly heat up your sample and take a long time, plus set up concentration gradients etc. You can initially add a high MW dye (polymeric) that is not incorporated into ice, at the price of some colligative effect which you can control for. $\endgroup$ – Buck Thorn Mar 22 at 16:14
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If you want a homogeneous distribution of dye, you will have to stir the solution. If you want to use electrophoresis, you need a charged dye.

Azo dyes used for hair coloring have colour and charge, for instance Basic Red 51 and Basic Yellow 87:

enter image description here

enter image description here

Of course, heat will increase the diffusion rate but will also disturb the water.

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  • $\begingroup$ Thank you for the response. Homogeneity is not that important. I just want to get some dye into all of the water. As I responded above, we have a slushy mixture of water and ice. I want to be able to distinguish between the two later. The idea is to quickly dye the water and the freeze the entire mixture. I would like to keep the shape of the composition. I will look into the two dyes you mentioned. $\endgroup$ – rxc370 Mar 22 at 15:35
  • $\begingroup$ You are welcome. If it has been useful to you, you might consider up voting and/or accepting the answer. $\endgroup$ – Raoul Kessels Mar 22 at 15:37

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