Phase Transitions 4

DSC00272The fourth phase of the Phase Transitions.

You may just look at this as a piece of abstract photography, and Svend Keller, when making these pictures, probably also looked at them from this perspective, with the attitude of a graphics artist and photographer.

On the other hand, as a material science teacher, he was also interested in the scientific side of it. If this aspect does not interest you, you might just stop reading here.

The crystallites of the low temperature phase are growing further, leaving only small rests of the previous configuration with the larger crystals striped by twinning (see previous posts). Some patterns of the previous dendritic growth pattern are still visible, perhaps as a result of different concentrations of the two components of this system, and the larger gaps are still visible. Apart from that, the crystals are “forgetting” their old structure. I don’t know if the gaps appearing black here were still filled with molten material or with another configuration (perhaps of only one of the two substances involved (Suberic acid and Phenyl salicylate (Salol))) that was not “optically active”, i.e. does not cause interferrence colours when interacting with polarized light.

Boat House

Boat_House

 

This small (12.7 cm x 9.1 cm) pencil drawing of a thatched, wooden shed, maybe a boat house, dated 31. January (?) 1947, is unsigned but was probably made by Svend Keller. I read the middle digit (denoting the month) as a 1, so it would have been made in January.

Since the scene does not look winterly, he probably made it after a photograph or other drawing or painting, as an exercise. The mirror image in the water does not seem to be very accurate if compared with the image of the house itself. This might be indicating that his artistic abilities where still developing.

However that might be, I like this little drawing for its atmosphere.

Phase Transitions 3

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The next phase transistion is taking place. In the previous one, whole cristals changed their configuration at once, in a process one may think of as a shearing of the whole molecular lattice. You may think of a group of soldiers turning on comand. The next phase transition, however, is a “civilian” transformation. Below a certain temperature, the old crystal lattice becomes instable. The transformation starts accidentally in some places, probably triggered by some faults in the crystal lattice. Then, one by one, molecules are shifting from the old to the new lattice, so the crystalites of the new conformation are growing bit by bit. For some time, the two phases coexist, but if the temperature goes down further, the new crystalites take over, obliterating most of the history of what was there before.

So from liquid to solid, from one solid phase to another solid phase and now to the third one, this is the fourth phase transition happening in this material.

Look at the previous phases of the Phase Transitions series to see more.

WAITING TO HAPPEN

nannus:

This is the second time I am reblogging a post of an artist I find remarkable on The Kellerdoscope. To me, the paintings of Ashley Sullivan are mesmerizing. Some are pure abstracts, some are landscapes, some are cityscapes or show industrial motives, with varying degrees of abstraction. Many of them are magic for me. I had a hard time deciding which of these paintings to choose. Just have a look yourself.

Originally posted on ASHLEY SULLIVAN:

36x36 AUGUST 2014

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AUGUST 2014

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Rolf Keller – In Memoriam

Rolf Keller

My grandfather Rolf Keller, the artist who created many of the drawings and paintings on this web site, as I remember him. He was fond of smoking, especially cigars. This picture was taken in a restaurant at river Elbe in Hamburg.

I think the film used was from East German (GDR-) production; all of these pictures have this violet tint. I decided not to try a color correction. This is how they are actually looking. They are contemporary documents and the properties of the film material are part of that.

The next one is also a slide, but on a black-and-white film. My father was a student back then and could not afford the expensive color slide films, so he used the cheaper black and white slide films instead or the color films from East German production that my grandfather brought along.

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This picture was probably taken in the port of Hamburg during a visit. Hamburg is in West Germany, Karl-Marx-Stadt, where Rolf Keller was living, was in the East. Young people were normally not allowed to visit the West, but for old people, this was possible. I cannot date these pictures at the moment, but might be able to do so later. In any case, they are from the 1960s.

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This picture is probably from the same visit to Hamburg as the first one.

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Rolf Keller’s grave in Chemnitz, photographed probably in 1984 (so the city’s name was still “Karl-Marx-Stadt”). It is displaying his 24-logo – he had started his business as a self-employed graphics artist in 1924. This grave probably does not exist any more.

All pictures: Svend Keller. The pictures are digitized slides or sections thereof.

Phase Transitions 2

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This is a view of the same material as in Phase Transitions 1. What has happened? Well, there was an intermediate stage. The lines visible in that one are maybe just cracks, but I don’t know. The material is cooling and that is putting it under some tension:
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But the third stage (the picture above) is different. What has happened there? The material has been cooling and then it underwent another phase transition, this time from one solid state into another solid state. The molecules in the crystals arranged themselves into another configuration. This is called a lattice transformation. Energy is released in this process. It is happening at a certain temperature during the cooling process.

The problem is that the angles of the crystals are changing during this transformation. As a result, the crystals don’t fit again into their places between the other crystals. They are put under tension. This is causing them to “zig-zag” in a process called “twinning”. You can see this at the border of the crystal. The lattice of molecules goes in one direction, then flips into its mirror image in the next section. The resulting stripes appear very quickly (with something like the spee of sound in the material). They appear not all at once but several of them might appear at the same time (as far as you can see). This changes the pattern of tension, so another set of stripes appears a moment later, and so on, until a relatively stable configuration is reached.

The result is a complex pattern of stunning beauty, with a mix of order and disorder.

The yellow section down in the center is a harbinger of things to come, but you will have to wait until next time before I am going to post that. And I am probably going to post some other stuff in between. So that is the cliff hanger here :-) .

The following pictures might illustrate what is happening in a crystal during twinning. This is, of course, a very simplified model (these models where built by Svend Keller for his material science lessons). The molecules in the organic crystals are not simple spheres, they have more complex shapes. But what you can see here are two octaedral crystals consisting of spherical “atoms” (plastic spheres), The third “crystal” in the middle shows an intermediate stage. The models consists of stacked layers of shperes. The spheres in each layer are glued together. If you push the blue sphere to the left, the middle “crystal” will “flip” from one configuration to the other. If you flip between the second and third image, you may get an idea what happens during twinning. This is also called lattice shearing.

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This is also called lattice shearing.

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All pictures: Svend Keller

Phase Transitions 1

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This is the first of a new series of posts that will show abstract photographs made by Svend Keller during the 1970s or 1980s (I don’t know exactly). I hope you will enjoy them. Actually, these are microphotographs. Details can be found in my previous article Organic Martensite.

A phase transition is a change from one phase to another. Phases are different states of matter, e.g. liquids and solids. On this image, you can see some crystals (colored areas, solid phase) and some rests of liquid, molten material between them (colorless areas, liquid phase). The colors are the result of an optical effect involving polarized light. In the crystalized areas, the molecules are ordered into a regular configuration, a crystal lattice. This ordered configuration has different optical properties in different directions, resulting in this optical effect. In the molten material, the molecules appear in all possible directions, so it has the same optical properties in all directions and does not influence polarized light in any specific way. The needle-like strokes are the first signs of another phase transition, from one solid phase to another one that has a different crystal configuration. More of that in later posts.

When the crystals start growing, they look like this (this is another sample and I don’t know if the same mix of substances was used):

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In this image, the molten liquid appears black, the crystals white or grey. You can see here that these crystals are branching (this is called dendritic growth). In the first picture, some crystals are parallel because the branched off from a common “parrent”. In fact, they are part of the same crystal.

One reason for the dendritic growth, i.e. the feather-like branching, is probably that the growing crystals increase the temperature in their surrounding (the phase transition results in the release of heat). Only a little distance away from one of the growing needles, the temperature is right again for the crystal to grow further, resulting in branching. This can happen in a fractal fasion.

There might be another reason contributing to the dendritic growth. The molten material is a mix of two different organic substances. In the crystals, these appear in some fixed ratio, depending on the structure of the crystal lattice. Of one component, there is more than what is “needed” in the crystals, the other one is a “minority component”. As a result of crystal growth, the remaining liquid is depleted of the minority component. Since the remaining substance for itself has a different (and in this case: lower) melting point, it remains liquid and the needles cannot grow thicker. Where a branch meets another one, it depleets the surrounding liquid, so the other crystal has some little indentation there because there was not enough material left (but this might also be a result of remelting because the newly growing branch releases heat). This is probably one of the reasons why the crystals branch: each branch reduces the minority component in the liquid around it, so directly besides the branch, the parent crystal cannot grow thicker. Only a little distance away there is anough of the other material again and another branch starts growing, resulting in a feather-like structure. These are just hypotheses, however. Some scientific research would be required to find out the exact mechanisms at work here.

However, you may leave this to the scientists and just enjoy the pictures for their beauty.

The blurring on the lower side is caused by the fast growth. If you watch this under a microscope, you can see the needles grow. The speed depends on the temperature. Unfortunately, I don’t have any film of this. It is fun to watch.

The motto of this blog is “Natural and Artificial”. Is this natural? Is it artificial? Or both? Maybe natureficial?