Photoacoustic monitoring of freezing-induced loading and freeze-casting processes.

Both freezing-induced loading (FIL) and freeze-casting (FC) are used for nano- and microstructured materials fabrication, including core-shell structures, shells, porous materials, as well as ceramics. The crystallization front velocity is a critical parameter for these techniques because it defines the period of lamellar structure during FC and FIL. Here, we show that the photoacoustic method allows us not only to detect the phase transition but also to measure the instantaneous velocity of the crystallization front and track ice crystal position during the crystallization of the sample. Moreover, we demonstrate the possibility of detecting a first-order phase transition in pure water using photoacoustics. Thus, the obtained results give the opportunity for in situ monitoring of the freezing-induced loading as well as the freeze-casting to optimize the parameters of nano- and microstructured materials.