In-situ understanding of pore nucleation and growth in polyurethane foams by using real-time synchrotron X-ray tomography

The nucleation and growth of pores in PU foams have been visualized and quantified for the first time in 4D using in-situ tomographic microscopy. Acquiring sequences of 3D images in 156 ms each, we describe homogeneous and heterogeneous nucleation and subsequent bubble growth dynamics for materials with and without nucleating nanoparticles. Exploiting the time resolved tomographic sequences we obtained the bubble nucleation rate, bubble density and size evolution, based on which the diffusion coefficient of gas molecules in polymer can be calculated, evidencing the reduction of diffusivity provoked by the inclusion of nanoparticles. We found that nucleation and growth are in a large extend decoupled in time