Phenomenology of bubble nucleation in the solid-state nitrogen-polystyrene microcellular foams

Experimental results on bubble nucleation in the solid-state polystyrene-nitrogen system are presented. It was found that the bubble nucleation occurs over a period of approximately 30 s, and is not instantaneous as previously suggested. Over the range of nitrogen pressures explored, 4-14 MPa, the cell nucleation density increased exponentially. However this increase was many orders of magnitude less than predicted by the homogeneous nucleation model, indicating that the classical theory may not be applicable to nucleation in thermoplastic polymers near the glass transition.