[JonDum]

Hello!

I'm wondering if all you chemists out there can help me with a little search, I'm sure it'll be fun . I'm looking for certain solutions that diffract light when it passes through them. Thus obtaining a similar effect like: http://www.rainbowsymphonystore.com/difgratglas.html

You know, when you put on those glasses and every light source looks like this:



So, what kind of solutions/mixtures will diffract light?

Thanks!

[cth]

If I understand, you want a solution that diffracts an incident beam light into several beams each with different directions, just like the picture?    Well, I wish you good luck. You'll need it because it's a very tough project... 

The problem is that liquids have a disordered and always moving structure. But, to have a diffraction phenomenon, you need a stable and periodic ordered structure. Needless to say, it won't be easy to have both together.

Explained in a simple way: You have diffraction when light comes across a structure with a periodic distance of the same order of the incident wavelength. All the particles reflects the incoming light and those reflections interact with each other to form constructive interactions (directions where there is light reflected) and destructive interactions (directions with no light reflected).

So, concerning your project, there are other ways to do it than to have the solution to diffract. For instance, you can put in the light path a metallic net with a mesh around 1 micron. I believe you can buy that type of net, but I have no idea of the price. If the net has the same color as the solution, it may go unseen and it will look like it is the solution that diffracts... 

[JonDum]

If I understand, you want a solution that diffracts an incident beam light into several beams each with different directions, just like the picture?    Well, I wish you good luck. You'll need it because it's a very tough project... 

The problem is that liquids have a disordered and always moving structure. But, to have a diffraction phenomenon, you need a stable and periodic ordered structure. Needless to say, it won't be easy to have both together.

Explained in a simple way: You have diffraction when light comes across a structure with a periodic distance of the same order of the incident wavelength. All the particles reflects the incoming light and those reflections interact with each other to form constructive interactions (directions where there is light reflected) and destructive interactions (directions with no light reflected).

So, concerning your project, there are other ways to do it than to have the solution to diffract. For instance, you can put in the light path a metallic net with a mesh around 1 micron. I believe you can buy that type of net, but I have no idea of the price. If the net has the same color as the solution, it may go unseen and it will look like it is the solution that diffracts... 

Thanks for explaining diffraction in an easy to understand way! So a liquid would be very hard to do, but what about semi-liquids? Say... a glue, or laminate? But with your definition of diffraction, I would also need a resonant structure within the mixture with a periodic nature (i.e. crystalline?). Is that possible?

Let's say I wanted to be able to spray this solution onto a sheet of glass or clear plastic, and then the entire sheet would then diffract light. That would be easier than a liquid that diffracts, correct?

[cth]

For a diffracting liquid, what you need is actually a compound that is liquid in normal conditions but that will crystallise perfectly when an external stimuli is applied (electrical field, temperature, mechanical pressure, light, magnetic field,... whatever). The crystalline form with a unit cell around a few microns should diffract nicely. Then, once the external stimuli is removed, the product returns to its liquid state... There is no physical law that says it is impossible to do. But I am afraid such a fine control over matter is still well beyond current technical reach. I doubt anyone on earth knows how to do that. 

That being said, there are always ways around a problem.  I think the idea of a spray onto a sheet of glass is at least possible, although not easy, if you accept to have only circular diffractions (to give you an idea, see the small picture named "A computer-generated image of an Airy disk" half way through the page http://en.wikipedia.org/wiki/Diffraction) instead of the discrete diffractions you showed on the picture.

The circular diffraction arises from a crystalline powder, as opposed to a single crystal with discrete directions. If you spray a compound onto a surface and it crystallises there, you'll end up with thousands of very small crystals (so called crystalline powder). There is practically no chance to get a nice single crystal from it. Simply said, a powder contains a large number of very small single crystals, each one of them diffracts with specific directions. Unfortunately, they are not in the same orientation in respect with one another. So, they all diffract with different directions. Overall, you end up with circles instead of dots.

So, for your project, you need to spray particles onto a surface where they should crystallise. Those spherical particles should have a size of a few microns if you want visible light to diffract. Importantly, the particles should be monodisperse (all with exactly the same size), or else they won't pack well. You'll need to find a way to mix them with a volatile solvent (ethanol for instance) just before you spray the mixture onto a surface. The solvent will evaporate, leaving behind the particles that hopefully will arrange themselves into an ordered pattern (you need to get lucky for that). Finally, for better effect, use a monochromatic light source (a laser). As well, you need to study the interactions between the particles and the surfaces (you don't want them to fall down as soon as the solvent evaporates...  ). OK, that's all I can think of.

As you realise, it is a very difficult project. And what you're doing is only a powder diffraction (circular) and not the single crystal (discrete light dots). Growing a single crystal onto a large surface is nearly impossible (you're more likely to win jackpot in a casino three times in row, than that happening).

[JonDum]

For a diffracting liquid, what you need is actually a compound that is liquid in normal conditions but that will crystallise perfectly when an external stimuli is applied (electrical field, temperature, mechanical pressure, light, magnetic field,... whatever). The crystalline form with a unit cell around a few microns should diffract nicely. Then, once the external stimuli is removed, the product returns to its liquid state... There is no physical law that says it is impossible to do. But I am afraid such a fine control over matter is still well beyond current technical reach. I doubt anyone on earth knows how to do that. 

That being said, there are always ways around a problem.  I think the idea of a spray onto a sheet of glass is at least possible, although not easy, if you accept to have only circular diffractions (to give you an idea, see the small picture named "A computer-generated image of an Airy disk" half way through the page http://en.wikipedia.org/wiki/Diffraction) instead of the discrete diffractions you showed on the picture.

The circular diffraction arises from a crystalline powder, as opposed to a single crystal with discrete directions. If you spray a compound onto a surface and it crystallises there, you'll end up with thousands of very small crystals (so called crystalline powder). There is practically no chance to get a nice single crystal from it. Simply said, a powder contains a large number of very small single crystals, each one of them diffracts with specific directions. Unfortunately, they are not in the same orientation in respect with one another. So, they all diffract with different directions. Overall, you end up with circles instead of dots.

So, for your project, you need to spray particles onto a surface where they should crystallise. Those spherical particles should have a size of a few microns if you want visible light to diffract. Importantly, the particles should be monodisperse (all with exactly the same size), or else they won't pack well. You'll need to find a way to mix them with a volatile solvent (ethanol for instance) just before you spray the mixture onto a surface. The solvent will evaporate, leaving behind the particles that hopefully will arrange themselves into an ordered pattern (you need to get lucky for that). Finally, for better effect, use a monochromatic light source (a laser). As well, you need to study the interactions between the particles and the surfaces (you don't want them to fall down as soon as the solvent evaporates...  ). OK, that's all I can think of.

As you realise, it is a very difficult project. And what you're doing is only a powder diffraction (circular) and not the single crystal (discrete light dots). Growing a single crystal onto a large surface is nearly impossible (you're more likely to win jackpot in a casino three times in row, than that happening).

Cth, that was immensely helpful. Thank you so much! I feel like you've given me a good starting point in this little personal project.

[cth]

No problem.  This idea looks very interesting.

Actually, diffraction phenomenon is used on a daily basis by crystallographers to determine crystal structures using X-ray radiation sources. You can find a very nice animation http://www.stanford.edu/group/pandegroup/folding/education/x.html where they rotate a single crystal: you see the diffraction spots moving on the animation. What I told you is based on my experience of crystallography, simply transposed to longer wave lengths. You can find as well a short explanation there http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0015966.html.

At first, you could try to put small particles in a glass container and you light a laser through it from below. You may want to shake the container gently, so the particles are forced to adopt a more compact arrangement. Imagine you have a glass and you pour quickly dry sand in it: the sand will be poorly packed with a lot of air in between. Then, if you shake it gently, the sand particles will start to aggregate more closely (with more order) and with less air in between. And it is better if you can get transparent particles, less light will be absorbed.

I hope it works. Good luck.