Bubble Growth In Poly (Methyl Methacrylate) And Carbon Dioxide Mixture

As an environmentally benign blowing agent,carbon dioxide(CO2)has a widespread application in polymer foaming process.In this paper,the nucleation and growth of bubbles in poly(methyl methacrylate)(PMMA)and CO2 mixtures were studied by molecular dynamics simulation.Firstly,we set up a coarse-grained carbon dioxide model and determined the intermolecular potential is Lennard-Jones(LJ).Comparing the simulation results with the experimental data,the model well predict the phase behavior of CO2.Secondly,we will incorporate carbon dioxide into PMMA chain polymer to foam a mixed phase and nucleate the system by changing the pressure.In this paper,we found that free volume-rich polymer segments could adsorb many small-size bubbles in the region close to the polymer chain.The existence of these small bubbles limits the number of free CO2 molecules,which is helpful for bubble stabilization.Moreover,the free volume of polymer segments decreases with an increase of startup pressure.As a result,the size of large bubbles becomes more uniform with a higher startup pressure.These results are useful for understand the curing process,and it can be used to guide the relevant process in foamed material industry.