Thermochromic paint (another idle musing)

[EBK]

Was thinking about the heat that electronic stuff gives off, and it led me to wonder if thermochromic paint (paint that changes color with temperature) could make an interesting enclosure finish, particularly for some noticeably warm circuits, e.g., amps and such, but perhaps other circuits as well.

Any thoughts?  I'd love to see someone with more free time than I have give it a try.

Imagine something where the control labels are the same color as the paint's cold color. 

[PRR]

Two words: Mood Ring.

[EBK]

Two words: Mood Ring.

Yes, that's basically it.  Is the idea tacky or pointless?

[PRR]

> tacky or pointless?

No; just a brain-spurt.

Everything has cycles. Mood rings were groovy once. That passed; is now long-past. The wheel goes round. I'll be interested to see what you come up with.

(I'm also realizing that there are huge fans of the new mood-ring pigments for cars and other stuff we don't see around here.)

[EBK]

Ok, I've decided to order some black thermochromic pigment in the name of science.

Most of the thermochromic pigments that are readily available change color at around 88°F (31°C).  It remains to be seen whether this will be useful or not, but it will be fun to find out. 

I'll probably experiment with paint on paper first, mixing the pigment with some Polycrylic, and perhaps applying a printed waterslide decal on top.

[EBK]

Thermochromic pigment arrived today, so the science has begun. 

Black thermochromic pigment was mixed with water-based Polycrylic (I didn't measure the ratio) and thinly spread on glossy paper.  My thumb and fingers contact the paper at the same time in this video.  It does turn impressively white when warmed to body temperature.

Here is the same thing but with aluminum flashing instead of paper.  The aluminum spreads out the heat, resulting in a slower change with a less distinct outline.

[EBK]

I'm encouraged by these results.  Aluminum enclosures are considerably thicker than aluminum flashing, of course, but I want to see if a small incandescent fuse light thermally coupled to the inside of a 1590A can effect a color change on the outside surface.  So, that's where I'm thinking experiment 3 may go. 

[karbomusic]

Two words: Mood Ring.

Holy crap, haven't heard of those since they were originally all the rage - what was that, 1975 ish?

[EBK]

Experiment 3.

I primed and painted a 1590A white, then covered that with a coat of the thermochromic paint (pigment mixed with Polycrylic again -- and, again, I didn't bother recording the ratio of pigment to medium). 

Here, I went with sufficient pigment density and paint thickness to essentially result in a solid black appearance.  It's rather sloppy, but good enough for this experimental phase.



And, here is the same enclosure after I placed it under my arm for a few minutes to uniformly warm it up.


It would probably take something very hot to warm this enclosure up to this temp from inside in a reasonably short time (the aluminum enclosure is an effective thermal conductor, naturally, and would act as a big heatsink).  However, I'm not terribly concerned about practical application yet.  I'm just having some fun with this stuff. 

[mth5044]

That's really cool!

[Mark Hammer]

Well yeah...when it's black.

Wouldn't you love to see a fingerboard painted with that stuff?  The fingerboard would keep changing tone as you moved your fingers around, or moved your hand up and down the neck.

[guidoilieff]

There is pigment for serigraphic paint that changes color with lower temperature and I think there is scientific tools that have even lower temperature reaction.

The best bet I guess is to heat on purpose the aluminium chassis with a resistor and some thermoconductive?  paste.

[EBK]

There is pigment for serigraphic paint that changes color with lower temperature and I think there is scientific tools that have even lower temperature reaction.

The best bet I guess is to heat on purpose the aluminium chassis with a resistor and some thermoconductive?  paste.

Yes, there are some pigments that change at lower temps.  I may eventually switch to one of those.

As far as heating, my latest idea, which came to me just this morning, is to buy a thermoelectric module and attach it to the inside of the enclosure:

I've always wanted to experiment with one of those anyway.   

[EBK]

Wouldn't you love to see a fingerboard painted with that stuff?  The fingerboard would keep changing tone as you moved your fingers around, or moved your hand up and down the neck.

I think a thermochromic neck would be interesting, but I'd have to get much better at playing so I wouldn't simply warm up a small portion of the fretboard.  My lack of skill would become too visible otherwise.   

Check out www.lingerprints.com

Thermochromic guitar bodies have been done too.

[karbomusic]

As far as heating, my latest idea, which came to me just this morning, is to buy a thermoelectric module and attach it to the inside of the enclosure

I have one... draws a boatload of current like an amp or few - Looked like more fun that it actually was.

[EBK]

As far as heating, my latest idea, which came to me just this morning, is to buy a thermoelectric module and attach it to the inside of the enclosure

I have one... draws a boatload of current like an amp or few - Looked like more fun that it actually was.

I'm currently eyeing up one that is spec'd 5V and 1A, but will apparently draw closer to 1.5A if you can supply it. Still not terribly practical, but could be usable for Experiment 4.   

I've also briefly considered using a 78xx voltage regulator's heatsink tab as a simple heat source and driving it right to the edge of thermal shutdown (just an exaggeration).  It would essentially be the same as the resistor idea, but with a nice thermal contact surface conveniently built in.  Has the additional bonus of being much much cheaper.

[Mark Hammer]

Wouldn't you love to see a fingerboard painted with that stuff?  The fingerboard would keep changing tone as you moved your fingers around, or moved your hand up and down the neck.

I think a thermochromic neck would be interesting, but I'd have to get much better at playing so I wouldn't simply warm up a small portion of the fretboard.  My lack of skill would become too visible otherwise.   

Check out www.lingerprints.com

Thermochromic guitar bodies have been done too.

As usual, I'm superb at predicting the past. 

[EBK]

You know, this thermoelectric module thing actually seems less impractical when I consider the fact that I have what is essentially a 90W wall wart just laying around unused  (19.5V, 4.62A):

[EBK]

Another quick vid, made while cooking some pasta for my kids:

The text says: "Translucency Test"

[EBK]

I now have a 5V, 1A thermoelectric module and a 5V, 3A UBEC (apparently, that is the term that the RC hobbyists use for a buck converter).  Hopefully, tonight will be science night again.

Update:
This is a bit less exciting, but still interesting.  Here is what 5W of heat does to the 1590A enclosure I showed previously.  It takes just shy of 2 minutes to completely change the color.

I'm now timing how long it takes the enclosure to return to black after disconnecting the power.  It will no doubt take much much longer than it took to heat up.

Update 2:
It took about 7 minutes for the enclosure to return to black.