Crystallization question

Linden.g · Post by **Linden.g** » Sun Apr 21, 2013 5:48 am

I did a food colouring timelapse video please see here http://www.flickr.com/photos/13084997@N ... hotostream
This shows some interesting behavour which I don't understand. If you look carefully you can see that some of the crystals which form as seperate crystals ahead of the main growth front appear to "slide" out of the top of the frame. They seem to dissolve at their back edge closest to the main growth front whilst reforming at their front edge, giving the appearance of movement. Does anyone have any thoughts on why this may occur?

rjlittlefield · Post by **rjlittlefield** » Sun Apr 21, 2013 11:09 am

Fascinating! The same effect, just more subtle, can also be seen about 1/4 of the way through, around pixel coordinates (330,240) on the trailing edge and invaginations of one of the big "fan" crystals.

I can only imagine that the initial crystal formation creates a structure that is slightly less stable then the one formed at the growing edge of a big well established crystal. In that scenario, concentration of dissolved material just ahead of the growing edge of a big crystal could get low enough to re-dissolve the less stable structures on the initial edges of other crystals.

But this is just what comes to mind. I don't recall reading anything about this.

--Rik

Jacek · Post by **Jacek** » Sun Apr 21, 2013 12:41 pm

great effect

curt0909 · Post by **curt0909** » Mon Apr 22, 2013 12:22 pm

I've never seen this before. Great video.

RogelioMoreno · Post by **RogelioMoreno** » Tue Apr 23, 2013 7:51 am

Very nice!

Rogelio

ChrisR · Post by **ChrisR** » Tue Apr 23, 2013 8:11 am

Could it be that energy released by the crystallization is raising the temperature enough locally to redissolve the crystal?

rjlittlefield · Post by **rjlittlefield** » Tue Apr 23, 2013 10:52 am

I like the temperature idea. It provides more opportunity for "action at a distance".

--Rik

ChrisR · Post by **ChrisR** » Tue Apr 23, 2013 12:26 pm

I was thinking it's bit fast for that, but of course we don't know!
What's the timescale, Linden?

I'm wondering if the solidification pushes or pulls on the coverslip, and whether that could have a "bearing". Don't think so.

Linden.g · Post by **Linden.g** » Tue Apr 23, 2013 3:36 pm

Some interesting ideas here. The whole event you see took about 1hr, approx 320 frame. I'm leaning towards Riks suggestion on different crystal forms. There a few things to note. This is a mixture of 4 food colouring. I also think that there is a bulk liquid movement towards the edge of the slide, which is at the bottom of the image (out of view), as the dry colouring at the edges of the coverslip wicks liquid out from the center. The middle of the coverslip always ends up the thinnest part of the slide after crystalisation has finished.

ChrisR · Post by **ChrisR** » Tue Apr 23, 2013 4:34 pm

Could be different phases (structures) of the solid. Would they polarize light differently?
Likely?
The circled area looks the same in polar light before and after the replacement though.
If the solid is a contraction (as expected, expansion of water is an odd one) then there would be a movement of stuff outwards.

Dunno!
Sorry if the pic repost offends, happy that it's removed if so. I don't know how Rik got coordinates!

Linden.g · Post by **Linden.g** » Tue Apr 23, 2013 5:03 pm

No problem with the repost Chris.

Ok so we would expect the front edges to grow because they have a flow of new solute and we would expect the more mature crystals lower down to slow down or stop as the liquid is depleted, its the loss of the back edge of the isolated crystals that has me lost. Perhaps the front edges of the bigger mature crystals are more favoured sites for growth and their top flat face is protected by glass due to their thickness. Perhaps the top face of the isolated front crystals are exposed because they don't touch the coverslip. This could then cause the bigger mature crystals to deplete the trailing edges and top face of the isolated front crystals causing them to both grow and dissolve in a concentration dependent rate. This then results in the movement along the slide. Very much in line with Riks idea.

ChrisR · Post by **ChrisR** » Wed Apr 24, 2013 12:47 am

--loss of the back edge of the isolated crystals --
Suggestion: as crystals "precipitate" from the solution, they take chemicals from the solution according to the structure being formed at the time, with its particular compositional requirements. Entropy Rules, lowest energy state is the target.
That will alter the concentrations in the remaining solute, which may mean conditions are less favourable for the solid form of other phases, causing them to redissolve. The edges which formed first (lower as we look at it) would be the ones furthest in composition from that of the solute, as time passes, and its concentrations change, so they'd redissolve first.

I don't know how the colours relate to the structures here. It's tempting to infer a link, which may not be there. Top left there's a brownish blob which scurries off the top of the frame. The growth in the area I marked, though, appears to be more continuous in appearance, to the growth below it.

Linden.g · Post by **Linden.g** » Tue Sep 02, 2014 4:33 pm

I think I've figure out what's going on in this video. The dye is probably in a liquid crystal state.

Linden