Distinguishing the glass, crystal, and quasi-liquid layer in 1-methylnaphthalene by using fluorescence signatures

Jan Zezula and David Mužík, led by Dominik Heger, collaborated with the Austrian group of Thomas Loerting to study the fluorescence behavior of 1-methylnaphthalene in the temperature range of 77-295 K. They discovered that the crystalline, glassy, and liquid states of 1-methylnaphthalene could be distinguished using fluorescence spectroscopy.

The authors found that the main distinguishing feature is the presence of excimer emission in the fluorescence spectra. Crystals do not show excimer fluorescence at temperatures below 190 K, unlike glass. The study also proposed the existence of a quasi-liquid layer on the surface of 1-methylnaphthalene crystals, characterized by excimer emission. This existence became apparent 40 K below the melting point.

Investigating freezing-induced acidity changes in citrate buffers

Susrisweta Behera, Radim Štůsek, and Lukáš Veselý, led by Dominik Heger, collaborated with the Austrian group of Thomas Loerting to conduct a comprehensive study of the behaviour of citrate buffer during freezing. The study revealed that one of the most commonly used citrate buffers becomes more acidic when frozen. Interestingly, the acidification is more pronounced at lower concentrations, while it is negligible at higher concentrations.

The authors conducted a calorimetric study and optical microscopy, correlating the results with the acidities obtained by spectroscopy. The study revealed that citrate buffer can crystallize, which challenges a long-standing paradigm in the pharmaceutical field. Additionally, the measured acidities demonstrate that citrate buffer significantly acidifies, which was previously unexpected.

Impact of secondary ice in a frozen NaCl freeze-concentrated solution on the extent of methylene blue aggregation

Lukáš Veselý and Radim Štůsek performed this study in cooperation with the A-ESEM microscopy group of the Czech Academy of Sciences. They were able to successfully connect microscopic images with spectroscopic data, which led to the first ever demonstration that the inner structure of the freeze-concentrated solution (as shown on the right) has a major influence on aggregation during freezing.

In this work the authors challaged a long standing theory, which assumed that the size of the ice crystals is the most important factor influencing the aggregation after freezing! This would not be possilble without close long-term collaboration of our research group with the ESEM group lead by Vilém Neděla.

Temperature and Concentration Affect Particle Size Upon Sublimation of Saline Ice: Implications for Sea Salt Aerosol Production in Polar Regions

The study was led by Dominik Heger in collaboration with the A-ESEM microscopy group of the Czech Academy of Sciences. The work focuses on the small (micrometre-sized) salt particles produced during ice sublimation. These particles are thought to facilitate photochemical reactions in polar regions.

In this paper, the authors show the surprising result that high-salinity ice requires temperatures of -30°C to produce particles small enough to form reactive aerosols. In contrast, in low-salinity ice, particles are produced at all sub-zero temperatures. This unique paper is the first to quantify the particle sizes produced by ice sublimation.

The importance of the article is immediately apparent as it has been chosen as the cover of the 8th issue of the 49th volume of Geophysical Research Letters.