Diffusion Of Small Molecules In Pla/pet Blends And Multiscale Modelling Of PLA/PA11Blends

As the most important tools in developing and designing materials, computer simulationshave been used widely in materials science, and promote the further development of materialsscience in a great extent. In this paper, molecular dynamics （MD） simulation method is usedto study the diffusion behavior of O₂and CO₂in polylactide （PLA）/polyethyleneterephthalate （PET） blends. Considering the multiscale properties of polymer blends, themultiscale simulation techniques from molecular dynamics （MD） to dissipative particledynamics （DPD）, then to the finite element methods （FEM） are presented to investigate therelationship between structures and properties of polylactide （PLA）/polyamide11（PA11）blends. In addition, DPD simulation method is used to study the effects of shear rates onmesoscale morphologies of PLA/PA11blends and the effects of amphiphilic blockcopolymers （A ’m-b-B’n） on the interfacial properties of PLA/PA11blends. There are mainlyfour aspects discussed in the paper:（1） The diffusion behavior of small molecules in PLA/PET blends estimated by MDsimulation. MD simulation technique is adopted to study the diffusion of O₂and CO₂in PLA/PET blends （with weight ratio at10/90,30/70,50/50,70/30and90/10）. The fractional freevolume （FFV） and morphologies of free volumes in PLA/PET blends are analyzed byConnolly surface method with the kinetic radius of O₂and CO₂as the Connolly radius. Thenthe Einstein’s relationship is used to calculate the diffusion coefficients of O₂and CO₂inPLA/PET blends. The results indicate that the simulated diffusion coefficients of O₂and CO₂in PLA/PET blends increase by the order of10/90>70/30>90/10>50/50>30/70, showing theidentical tendency as the FFV. Moreover, the diffusion coefficients of O₂are larger than CO₂in the same blends. （2） Compatibility of PLA/PA11blends estimated by MD simulation. PLA/PA11blends（with weight ratio at10/90,30/70,50/50,70/30and90/10） are investigated by atomistic MDsimulation. The Gibbs free energy, Flory-Huggins interaction parameters, radial distributionfunctions, X-ray diffraction spectrogram and hydrogen bonds suggest that PLA/PA11blendsare immiscible. This is consistent with the experimental results in literature.（3） Mesoscopic simulation of the binary PLA/PA11blends and ternaryPLA/PA11/A ’m-b-B’nblends. DPD simulation method is used to study the mesophaseformation of PLA/PA11blends and the effects of shear rates on the mesoscale morphologiesof the blends. The results indicate that the morphologies of PLA/PA11blends are closelyrelated to the blend ratios and interaction parameters between the blend components.Moreover, shear rates determine the phase transformation induced by shear. For the ternaryblends, the effects of concentration, length and structure ofA ’m-b-B’non interfaceproperties of PLA/PA11blends are investigated by DPD simulation.（4） Macroscopic mechanical properties of binary PLA/PA11blends and ternaryPLA/PA11/A ’5-b-B’5blends. FEM is used to study the mechanical properties of PLA/PA11blends, the elastic modulus in xx, yy and zz directions show that10/90and90/10PLA/PA11blends are isotropic materials, while30/70,50/50and70/30PLA/PA11blends are anisotropicmaterials. Moreover, adding the amphiphilic block copolymer increase the interfacial stress ofPLA/PA11blends. At the same time, the interfacial stress increase with increasing theconcentration of block copolymer.