Tracing coffee tabletop traces
Jork Leiterer1, Franziska Emmerling, Ulrich Panne
1BAM Federal Institute for Materials Research and Testing, Richard-Willstatter-Strasse 11, 12489 Berlin, Germany.
Langmuir : the ACS Journal of Surfaces and Colloids
|June 28, 2008
Summary
Caffeine crystallization on surfaces forms coffee rings with mixed alpha- and beta-caffeine crystals. Acoustic levitation yields only alpha-caffeine, suggesting surface effects influence crystal polymorphs.
Area of Science:
- Materials Science
- Chemistry
- Crystallography
Background:
- Crystallization is fundamental to chemistry, pharmacy, and medicine.
- Understanding micro- and nanocrystal formation is crucial for various applications.
- Caffeine-water solutions serve as a model system for studying crystallization.
Purpose of the Study:
- To investigate caffeine crystallization from aqueous solutions under ambient conditions.
- To analyze the influence of surfaces versus acoustic levitation on caffeine crystal polymorphs.
- To explore controlled formation of cocrystals and novel polymorphs.
Main Methods:
- Evaporation of aqueous caffeine droplets on surfaces (glass, polystyrene, polyester).
- Analysis of resulting "coffee tabletop" rings using micro focus X-ray beam.
- In situ synchrotron X-ray diffraction of ultrasonically levitated caffeine droplets.
- Atomic Force Microscopy (AFM) for nanoscale particle analysis.
Main Results:
- Stable "coffee tabletop" rings of caffeine crystals formed upon droplet evaporation on surfaces.
- Both alpha- and beta-caffeine crystal modifications were found, locally separated within the rings.
- Acoustic levitation resulted in pure alpha-caffeine, without the beta-caffeine polymorph.
- AFM revealed nanoscale particles in addition to microcrystals.
Conclusions:
- Surface interactions significantly influence caffeine crystallization, leading to the presence of both alpha- and beta-polymorphs.
- Acoustic levitation, free from surface effects, yields only the alpha-polymorph.
- These findings offer new possibilities for controlling the formation of micro- and nanocrystalline materials, including cocrystals and novel polymorphs.
- The study has implications for pharmaceutical and medical applications requiring precise control over crystal forms.
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