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Multiple scattering of laser radiation by the structure of forming porous matrices gives rise to spatiotemporal intensity fluctuations in the field of scattered radiation (dynamic speckle modulation). Dynamic scattering of laser radiation in the volume of evolving foams was used to study the process of formation of highly porous polylactide matrices during their synthesis by the method of supercritical fluid foaming in a carbon dioxide medium. The average lifetime τ lt of dynamic speckles, which were recorded by a high-speed CMOS camera, was taken as a parameter carrying information on the ensemble-averaged mobility of scattering centers (boundaries of developing pores). A phenomenological model was developed, which established the relationship between the current values of τ lt , macroscopic parameters of the foam (volume and the rate of its change), and the ensemble-averaged microscopic mobility of interfaces (the first derivative of the average pore size with respect to time). The developed model was used to interpret experimental data on the dynamics of polylactide foam expansion during fast (0.03 MPa/s) and slow (0.006 MPa/s) depressurization of supercritical CO 2 in the reactor. It was determined that in the case of fast depressurization, structural rearrangements in the foam volume continue even after the foam reaches the maximum value of the expansion factor. This feature was qualitatively interpreted based on the concepts of thermodynamic nonequilibrium of porous matrices during their formation.

Various approaches to the optical diagnostics of evolving polymer foams formed as a result of a decrease in the external pressure according to a given scenario in the “polymer-supercritical fluid” systems are considered. Formed polymer foams are considered as a material platform for the creation of scaffolds for biomedical applications. Diagnostics of the current state of the foam was carried out by statistical analysis of the spatiotemporal fluctuations of the probe laser radiation, multiple scattered in the volume of the evolving foam, or by analyzing the fluorescent response during foaming of the “polymer-fluorophore” mixture, pumped by laser radiation in the absorption band of the fluorophore. A relationship has been established between the average lifetime of dynamic speckles in scattered laser light and a generalized parameter characterizing the foam expansion dynamics. It was also found that the waveguide effect in the walls of the formed pores has a significant influence on the fluorescent response of the evolving foam, leading to an increase in the characteristic dwell time of fluorescence radiation in the walls and, accordingly, to an increase in the contribution of the induced component to the fluorescent response.