ABSTRACT
Bubble nucleation can be described as an event where a second phase is generated from within a metastable single phase. In Y. Kagan’s analysis, the rate of nucleation is governed by the rate of vaporization of molecules from the liquid-gas interface into the bubble. Ruengphrathuengsuka observed that the number of bubbles nucleated increased with increasing temperature, owing ostensibly to the drop in surface tension and melt viscosity as temperature increased. Heterogeneous nucleation results in the formation of a smaller number of bubbles than homogeneous nucleation, because the number of bubbles in a heterogeneous system is limited by the number of the dispersed particles of the second phase. The resulting reduction of concentration of gas in the polymer affects the rate of homogeneous bubble nucleation, and therefore a time dependent concentration expression needs to be used in the place of a constant concentration.
