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Capturing the Freeze-Drying Dynamics of NaCl Nanoparticles Using THz Spectroscopy
journal contribution
posted on 2018-10-11, 14:04 authored by Katsuhiro Ajito, Yuko Ueno, Jae-Young Kim, Takashi SumikamaSodium chloride (NaCl)
aqueous solution becomes NaCl hydrate, NaCl·2H2O,
at low temperature, which is different from potassium chloride
and is a typical complex model for studying the freeze-drying process
in foods and pharmaceuticals. Here, we detected unit-cell-sized NaCl
particles in ice as precursor substances of NaCl·2H2O during freezing of NaCl solution by using terahertz (THz) spectroscopy.
In the freezing process, Na+ and Cl– ions
form two types of metastable unit-cell-sized NaCl particles on the
pathway to the well-known NaCl·2H2O crystal production,
which are not listed in the phase diagram of freezing of NaCl solution
but have absorption peaks in THz spectra. This finding of single unit-cell-sized
particles signifies the importance of studying the freeze-drying process
in-depth and offers a new possibility for the development of freeze-drying
technology for the manufacture of nanometer-sized particles such as
ultrafine pharmaceutical powders, which more readily dissolve in water.