Advanced Technique for In Situ Raman Spectroscopy Monitoring of the Freezing-Induced Loading Process.

The freezing-induced loading (FIL) method is a promising technique for encapsulation of bioactive substances as well as for preparation of nanocomposite materials. A critically important aspect for this method is the remote control of the freezing process. The knowledge of the moment of freezing process ending can allow us to increase the quality of loading and reduce the process duration, thus making this approach more controllable. Herein, we present a photonic technique based on Raman spectroscopy as one of the optimal solutions for remote control of FIL. As a result of our study, the setup for obtaining Raman spectra during the process of liquid vehicle crystallization in suspensions has been developed, which allowed us to analyze the sorption of nanoparticles onto micro- and submicron particles by the FIL method in situ. The main focus of the present work is the in situ Raman spectroscopy monitoring of the crystallization process, including technologically important parameters such as the ice/water interface velocity in water colloids/suspensions and the moment of the final adsorption of the nanoparticles on the microparticles. In contrast to other approaches, Raman spectroscopy allows to directly observe the hydrogen bond formation during crystallization. Additionally, a schematic and a detailed description of the setup are presented here. Thus, the developed technique has a good perspective for scaling up the FIL approach and increasing the area of application of this technology.