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):
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?