Key words: polylactide, foaming, supercritical carbon dioxide, laser radiation, dynamic scattering, mobility of interphase boundaries
Multiple scattering of laser radiation on the structure of forming porous matrices results in spatiotemporal fluctuations of intensity in the scattered radiation field (dynamic speckle modulation). Using the effect of dynamic scattering of laser radiation in the volume of evolving foams, the process of formation of highly porous polylactide matrices during their synthesis by the supercritical (SC) fluid foaming method in a carbon dioxide medium is analyzed. The average lifetime of dynamic speckles, τlt, which are recorded using a high-speed CMOS camera, is considered as a parameter carrying information on the ensemble-averaged mobility of scattering centers (boundaries of developing pores). A phenomenological model has been developed that establishes the relationship between the current values of τlt, macroscopic parameters of the foam (volume and rate of its change) and the ensemble-averaged microscopic mobility of interphase boundaries (the first derivative of the average pore size over time). The experimental data interpretation using the developed model on the dynamics of polylactide foam expansion during rapid (0.03 MPa/s) and slow (0.006 MPa/s) pressure release of SC-CO2 in the reactor are presented. It is established that in the case of rapid pressure release, structural
rearrangements in the foam volume continue even after it reaches the maximum value of
the expansion factor. A qualitative interpretation of this feature is given based on the
concepts of thermodynamic nonequilibrium of porous matrices during their formation.
doi:10.34984/SCFTP.2024.19.3.004