Welding dynamics in an atomistic model of an amorphous polymer blend with polymer–polymer interface

Abstract

We consider an atomistic model of thermal welding at the polymer‐polymer interface of a polyetherimide/polycarbonate blend, motivated by applications to 3D manufacturing in space. We follow diffusion of semiflexible chains at the interface and analyze strengthening of the samples as a function of the welding time tw by simulating the strain–stress and shear viscosity curves. The time scales for initial wetting, and for fast and slow diffusion, are revealed. It is shown that each component of the polymer blend has its own characteristic time of slow diffusion at the interface. Analysis of strain–stress demonstrates saturation of the Young's modulus at tw = 240 ns, while the tensile strength continues to increase. The shear viscosity is found to have a very weak dependence on the welding time for tw > 60 ns. It is shown that both strain–stress and shear viscosity curves agree with experimental data.

Two-Step Heat Fusion Kinetics and Mechanical Performance of Thermoplastic Interfaces

“…As the TCs are enhanced with longer fusion time, the strength is largely improved, while the increased TCs have a minor effect on modulus. This contrast in the t-dependence of Young's modulus and tensile strength was also reported in previous studies 15,16 . The effects of viscosity are shown in the results with different chain lengths (Fig.…”

“…Molecular dynamics (MD) simulations identify two different stages of inter-diffusion, where the first stage is faster than the second one 15,16 . This finding can be explained by the existence of unequilibrated chain ends and vacancies on both sides of the interface in the initial stage where diffusive processes dominate 16 . The interfacial confinement on polymers increases as the diffusion proceeds, involving more significant entanglement effects 15 .…”

“…This proposal can also be supported by the recovery of mechanical properties at the interface. While polymer melting dynamics predicts that the polymer chains should diffuse by a distance on the order of their radius of gyration to fully erase the memory of structural information at the interfaces, experimental 17 and simulation 7,15,16 studies suggest that the bulk strength can be recovered at much earlier time, due to the established entanglement between polymer chains that controls the interfacial strength and plastic responses 9 .…”

Effect of flow-induced molecular alignment on welding and strength of polymer interfaces

“…Chemically detailed models are needed to make quantitative predictions of strength, but are difficult to use on the time scales needed for highly entangled polymers to interdiffuse. 46 Different mechanisms may be important for semicrystalline polymers or polymers with multiple monomers, such as acrylonitrile butadiene styrene (ABS). Rather than being constrained by entanglements, the relative motion of chains may be constrained by crystal order or segregation of monomer species.…”

Two-step heat fusion kinetics and mechanical performance of thermoplastic interfaces

“…Molecular dynamics (MD) simulations identify two different stages of inter-diffusion, where the first stage is faster than the second one 22 , 23 . This finding can be explained by the existence of unequilibrated chain ends and vacancies on both sides of the interface in the initial stage where diffusive processes dominate 23 . The interfacial confinement on polymers increases as the diffusion proceeds, involving more significant entanglement effects 22 .…”