Two-dimensional crystals
The two-dimensional crystals described here were investigated by the Chilean-German physicist Mario Markus [1] [2] [3]. They can be a complement in physics or chemistry classes held in schools. They grow under a microscope on a glass slide, usually within a few minutes by a mechanism analogous to "ice flowers" or frost on windows. Thus, they differ from crystals that grow in three dimensions in a saturated solution. The shapes of the two-dimensional crystals vary depending on the solvent (for example, water or ethanol), temperature, humidity, thickness of the solution, and concentration of the solute.
Comparison with crystals in three dimensions
Three-dimensional crystals have symmetrical shapes, for example cubes or octahedrons, which are often seen in jewelry. They are formed by sequential binding of molecules, which remain in the most stable positions. Adhered molecules with little stability must have time to detach from the crystal. This requires that the formation of the crystal may require long times: hours, days or more. In contrast, the two-dimensional crystallizations described here take place in extremely short times, because the layer of solution applied on the glass slide dries quickly.
Unlike crystals in three dimensions, no two-dimensional crystal is the same as another. This is because the motion of the molecules in the solution is chaotic and there is not enough time to detach unstable and random adhesions of molecules. Of course, in some cases the time is sufficient for orderly adhesions, which altogether leads to a mixture of order and chaos.
Procedure
- Weigh the required quantity of the substance (or substances if it is a mixture).
- Dissolve the substance(s) in water or other solvent, stirring. Heat if necessary.
- Place a drop of the solution with a pipette in the center of the slide. The next point 4 can be skipped if the drop of solution (e.g. 50 ml) smears easily on the slide. If this is not the case, proceed as follows: Spray the slide with a hydrophilic substance, for example with windscreen anti-mist spray. Then put a tissue on top and press lightly to make the foam disappear. Let dry.
- If the drop does not spread, use a glass rod to distribute it over the entire slide.
- Wait until the solution layer dries. If it takes too long, it is useful to place and press a few crystals of the solute on the shore.
- Move the slide under the microscope until an interesting framing is discovered (usually about one millimeter by one millimeter) using transmission and not reflection of light. In general, figures with gray values are obtained.
- Photograph the observation by the microscope. With a suitable algorithm, such as GIMP, gray values can be changed into colors.
Examples
Two-dimensional crystals obtained with different substances are shown below.
References
- ↑ Mario Markus (2019), Scientia et Ars, UC Editions, ISBN 978-956-14-2469-2 (Spanish)
- ↑ Markus: Bildkraft der Substanzen: 2D-Kristalle zum Selbermachen, Arnshaugk Verlag, Neustadt 2017, ISBN 978-3-944064-77-2 (German)
- ↑ Mario Markus: Zweidimensionale Kristalle, MNU (Mathematischer und Naturwissenschaftlicher Unterricht) 3 (2018) pp. 195-205 (German)
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