Science Buddies: "Ask an Expert"

Hi all - I'm actually not a science teacher but an art teacher with a keen interest in science. I find a scientific approach, particularly with regard to materials, is critical to the work of an artist looking for the best materials to use for the effective realisation of an idea.

My specific question at the moment regards a project my high school students are working on: it will involve a screen that should gradually soak up coloured water, eventually staining the screen itself.

The screen would be a textile that will hang vertically down to the ground but with with several meters excess length allowing them to stretch it out along the floor too - so that it will lie flat on the ground under a container that will intermittently spill the liquid onto it.

My question is, basically, what material (white, or off-white) could the 'screen' be of in order that the water should be carried up the vertical part by capillary action? Note that I don't necessarily need a material that will suck up water extremely fast - indeed it would be better if it takes a while before the screen begins to be discoloured (the installation would be in place for several days and the students want it to evolve over time). Also, should you happen to know of a material that might suck up coloured water in such a way as to leave interesting discolouration patterns in its wake as it dries, that could be very exciting for them (I told them not to get their hopes up, but you never know).

Obviously, being an art department, budget is a very limiting factor, so if you could suggest certain fairly standard materials I'd be very grateful - would felt be better than cotton for example, or does the tendency to absorb and retain liquid not correlate necessarily with the capacity to suck water up vertically?

Forgive my laymen's terms - I hope my question is clear enough for you. Please don't hesitate to ask for clarification if you're interested in the question but unsure exactly what I mean.

Thanks in advance for your time. I've tried researching on the web but it's hard to search when you don't know exactly what you're looking for.

This is my first post here. I really hope that the idea of helping an art teacher/science enthusiast will interest you - there is a bizarre and totally artificial social division of art and science that I make it one of my pet obsessions to dissolve.

Hi Adamjbw,

I haven't tried this experiment myself, but I suspect that cotton (e.g., muslin) would work well for this. If you're planning to do this over several days, keep in mind that water will be evaporating from the fabric. You will probably need to keep the bottom of the fabric quite wet so that water will continue to "climb" up the material. You might try a little experiment with small strips of different fabrics suspended over a string, with the bottom of the fabric strips in a pan of colored water, to see which fabric works the best, as well as to get a feel for how high up the colored water will travel.

This sounds like a fantastic installation!

I agree that cotton would be a good, budget friendly material to work with. Cotton does exibit a capillary like effect although I don't believe it is technically the same mechanism.

Synthetic materials (nylon, etc) would not work as well. Other natural fibers would work (wool has even better wicking abilities) but are much more expensive. I think muslin is your top choice.

oh wow thanks for the replies Terik and Audrey - I thought I'd get an email letting me know someone had replied but it appears not.

Thanks for your suggestions - indeed it's time to experiment now (art and science are so clearly related - much less rigor in artistic experimentation, but the same motive for trying new things, figuring things out, solving problems, etc.).

We have already had some disappointing results with tests using cotton (though haven't tried muslin), where the water rose only a short way up then stopped. I guess capillarity can only combat gravity so far huh? I don't grasp this intuitively... just because the water has climbed doesn't change it's mass... is it the cumulative mass of all the water that has climbed so far that is relevant?

Do you know of anything we can do to increase the capillarity? A different liquid perhaps?

Do you think something like felt would be more effective, or that sponge-like squishy material - or something called capillary matting that is used for growing seeds?

Assuming we can solve the capillarity problem, I was thinking of using coal or household dirt or earth (clay or soil) to discolour the water, but am concerned that these might fail to 'climb' up the screen with the water... What do you think?

Obviously all this needs to be experimented. But if someone who understands the mechanics of capillarity can help us on our way, or point us towards trying certain materials, that would really be great.
Thanks very much for any thoughts you might be able to provide.
All the best,
Adam

Hi Adam,

It doesn't surprise me that the water didn't travel all the way up the fabric. The mass of individual water molecules won't changed, but evaporation is removing water from the cloth. You'll end up in a situation where the rate at which water can be drawn up through the fabric (at a given distance) balances the rate of evaporation. At that point, the water won't travel any further.

Dirt will not travel up the fabric. Some compounds in the soil may dissolve in the water and travel up the cloth with the water, until evaporation forces them out of solution. That may lead to discoloration. But particulates will not travel up the material. I suspect you will get the best results using a dye of some sort (e.g., food coloring). The discoloring substance needs to dissolve in the water.

As far as different liquids go, I think water is probably the safest and effective solvent for your purposes. You don't want a vat of rubbing alcohol, for example, sitting in your classroom. Water is also helpful because it is a polar molecule. The polarity of the water molecule is part of what makes capillary action work. However, as audreyln pointed out, the mechanism at work in this situation is most likely capillary-like, not exactly capillary action.

For materials - the best advice I can give is to try them and compare the results. Filter paper works well for small chromatography experiments, but I'm not sure you'll be able to find it in the long rolls that I think you are talking about. You could do a small-scale test where you suspend a pencil or rod across the top of a tall glass and then drape a piece of felt, etc. across the pencil or rod. Then fill the tall glass with water until the water barely touches the bottom of the pieces of material and observe how far the water travels up the material.

You may also find the background material and procedure in these Project Ideas relevant. By introducing a dye, you are essentially doing a chromatography experiment:

https://www.sciencebuddies.org/science- ... ml#summary
https://www.sciencebuddies.org/science- ... ml#summary

Thanks Terik - we'll carry out a number of experiments next week.

The rate of evaporation will be quite high I suspect, given that the light of a powerful spotlight will be reflected onto the screen. We'll see what results we can get and adjust the project accordingly: art is all about mediating between imagination and reality.

Just a last stab in the dark - can you think of any treatment of the material that might enhance the capillary-like action? Would it be conceivable to apply some kind of impermeable film to the surfaces to reduce evaporation, for example? I'm thinking cling-film, as I can't think of anything that wouldn't itself soak into the fibre if applied liquid... but it might be ineffective aesthetically speaking - how far has research progressed into graphene - can't buy graphene films at the supermarket yet can we? (; Ah that'll be the day!)

hey... just a mad idea that probably makes no sense... but what if the water is salted? when it evaporates on the screen, leaving a salt deposit, could there be an osmosis effect that might work in tandem with the capillary?
Also, do you think maybe some kind of paper might work even better than cotton? Finding toilet roll works pretty well, but hard to find in the dimensions we need...

the more research I do the less likely it seems to me that we'll be able to raise water above a metre in the cloth... even above a fraction of that seems tricky... technical felt is listed at 5.5 inches vertical wicking... which is as good as it gets so far as I can tell... though that figure will have been taken after a limited time, the curves flatten out quite a lot as time goes on so I doubt it will go beyond a foot in a week...
I'm wracking my brain trying to think of something that would increase the upward force acting on the liquid against gravity...
but I'm losing hope...
Perhaps the way forward will be to have the screen as a wide belt on a motorised roll (like a film reel), so that it actually passes through the water. Could be interesting to have the screen moving like a reel of film... Can think of nothing else right now.
Perhaps we should scrap the whole screen-wetting angle and focus on the rest - perhaps accentuating the cumulative effect of crisis after crisis by having the water fall into a steel tray that will rust over time.
We shall see.
Thanks all for your help anyway.

Hi Adamjbw,

I agree that working to get a material to (using your phase) "vertically wick" several feet isn't realistic. Best of luck with your other ideas!