Help with a non-water based conductive liquid at room temp.

P_S_K

Really hoping someone can help here!

Im a product designer, not a chemist/physicist so apologies in advance for any stupid questions. I'm developing a new table lamp which is turned on and off by tilting it. For prototypes I have used a carbon based conductive ink but this isnt really suitable.

I have looked at things like woods metal, mercury and gallium indium tin, but all of these have various problems - too high melting point, toxic, and wets to glass very easily!

I really hope someone can offer some opinions!

0xDEADBEEF

Do you need any design aspect of the liquid? Otherwise this is a problem that can be solved by force sensors through other means. I am sure you can find a manufacturer that makes tilt switches without mercury. The industry needs them and mercury switches have been phased out.

P_S_K

the system works in the same way old mercury tilt switches did, but scaled up and using mains voltage. A small tilt switch and relay could be used, but the whole point of the design was to be able to see the elegance of the liquid joining the contacts.

Borek

Eons ago we used an epoxy resin with silver fillings for gluing carbon electrodes to the copper wires. I wonder if some kind of silver nanoparticles suspension in a liquid viscous enough to not allow fast sedimentation won't work.

0xDEADBEEF

I expected that it was all about the optical design issue... I would try to work with Galinstan and try to take care of the wetting issues by coating the glass container with something strongly hydrophobic.

chemisttree

You are limiting yourself by basing your switch on designs that use conductive liquids. Those devices are easily manufactured but at the cost of health and safety.

How about an enclosed ball bearing that bridges contacts at the end of a linear race?

RocketSci5KN

You could also consider a mildly conductive liquid, such as salt water, perhaps with additives to make it look metallic if necessary. This would activate a separate low Ron switch for the main power conduction.

P_S_K

This is a good idea - and might work even with carbon nanoparticles to keep cost down. In the original design, the conductive ink was submerged in oil (baby oil!) to help it flow smoothly. Some form of resin might work with the oil?

P_S_K

Yeh just need to get my hands on some to experiment. I found that the last conductive ink I used required the glass to be coated with a hydrophobic solution too - but his was just an off the shelf solution. Not sure if it would work with galinstan, but only one way to find out I suppose.

P_S_K

Although it may be slightly limiting, using the conductive liquids is a key characteristic of the project, so I'd like to persevere as much as I can. The health risks of the likes of mercury are considerations, and I'm trying to avoid using it at all costs. The liquid will be fully and securely contained inside, but there is always the risk.

P_S_K

This is something I had thought about too, but would require a bit of a redesign of the product to fit in the extra components. Its not out of the question, but I'd like to exhaust the options of solely using the conductive liquid first.

P_S_K

thanks for all the input guys! Is very helpful - hopefully edging closer to a solution.

Borek

If memory serves me well, glass is not wetted by gallium when it is coated with a transparent layer of gallium oxide.

P_S_K

Hmm thanks Borek, gallium oxide sounds promising. I'll do a bit of research into this.

Velikovsky

Have you considered a solution of sulphuric acid? It's very stable and an excellent conductor.

Borek

Highly corrosive. Besides, water from the solution gets electrolyzed, which generates another problems.

Velikovsky

True it is very corrosive, but a liquid solution only requires 1% sulphuric acid to become conductive! at that concentration it's less corrosive than vinegar. A switch such as mentioned in the original comment should only be drawing milliamps for a fraction of a second to activate the main current for the lamp. I was only considering possibilities anyway. But I do know that a mercury or sulphuric switch would never pass health and safety regulations for domestic use in any case. A reed switch from Radio Shack would perhaps be more sensible.wink:)