In situ ETEM study of water condensation / evaporation and the hygroscopic behavior of aerosols using a Peltier micro-device cooled holder tip
Résumé
The constant development of atmospheric closed cells since a few decades permits today a wide range of in situ studies of nanomaterials in liquids, or liquids themselves in a Transmission Electron Microscope (TEM). However, Liquid Cell TEM fails to properly study liquid-vapor reactions of utmost importance in many societal subjects especially concerning water interactions with nanosystems, such as in atmospheric chemistry (see e.g. [1]) or in pharmaceutical sciences [2]. Such domains can fortunately be tackled in a dedicated Environmental TEM (FEI Titan ETEM), where the absence of sealing membranes around the sample allows direct exchanges between the vapor (gas) introduced into the microscope and a solid. Several studies exist of the hygroscopic behaviour of model or atmospheric aerosols in such ETEMs, e.g.[3]. A cryo-holder is used to cool down the specimen (typically in the range 0 to 18 °C) in order to reach the vapor-liquid equilibrium in the pressure range eligible in an ETEM (below 20 mbar).
A new approach is reported, where the sample is cooled by means of a micro-Peltier stage mounted on the type of a commercial MEMS-based ‘heating holder’ from DENSsolutionsTM, see Fig. 1a). This montage [4] offers a bunch of advantages as compared to the above ETEM approach. One being its rapidity to reach a given relative humidity (linked to the temperature-pressure conditions), which allows to study accurately the first stages of deliquescence (dissolution) or efflorescence (recrystallisation) of soluble solids, such as NaCl nanocubes as illustrated in Fig. 1 b-d). Transient states just before the deliquescence (efflorescence) of the crystals will be described, such as shape oscillations attributed to local dissolution / reprecipitation events, see Fig. 2 [5].
References:
[1] 1] A.G. Tereshchenko. J. of Pharmaceutical Sciences, 104 (2015), 3639.
[2] Y-L. Pan et al., J. of Aerosol Science, 155 (2021), 105767.
[3] M.E. Wise et al., Aerosol Science and Technology, 42 (2008), 281.
[4] J.V. Vas et al., Microsc. Microanal. 28, S1 (2022), 818.
[5] Thanks are due to CLYM (www.clym.fr) for the access to the microscope. This study is supported by the French National Research Agency (ANR) under the ‘WATEM’ project n° ANR-20-CE42-0008.