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We employ molecular dynamics (MD) simulations to investigate the mechanical behaviors of immiscible polymer interfaces enhanced by block copolymer compatibilizers. We show that the entanglement density at the interface, governed by the Flory–Huggins parameter χ, is critical for mechanical performance. Increasing immiscibility leads to sharper interfaces with reduced interfacial entanglements, resulting in easy chain pullout during tensile deformation and weaker interfacial strength. Adding block copolymer compatibilizers to the blends can switch the failure mechanism from interfacial chain pullout to bulk-phase crazing, substantially enhancing mechanical performance. Although long diblock and tetrablock copolymers only mildly increase the interfacial entanglement density, they can act as stress transmitters across the interface by entangling with chains in the bulk domains. Tetrablock copolymers are particularly effective for strengthening polymer blends by forming loops at the interface, making chain pullout topologically more difficult and promoting energy dissipation through crazing in the bulk regions. Our findings reveal the roles of both entanglement at interfaces and block copolymer architecture in the mechanical properties of immiscible polymer interfaces, which may guide the design of better compatibilizers for enhancing inhomogeneous polymer samples.
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Polystyrene and poly(methyl methacrylate) interfaces reinforced with diblock carbon nanotubes
Abstract An asymmetric double cantilever beam test was used to determine the ability of carbon nanotubes with varying chemistry along their lengths, that is, diblock nanotubes, to compatibilize the polystyrene/poly(methyl methacrylate) (PS/PMMA) interface. PS molecules were grafted primarily to one of the blocks to cause that block to migrate to the PS phase since otherwise both blocks would prefer to reside in PMMA. Fracture toughnesses increased monotonically with increasing diblock carbon nanotube concentration and maximum values were like those for block copolymer‐reinforced interfaces while single‐chemistry nanotubes showed no reinforcing effect. However, the abrupt increase in fracture toughness with added compatibilizer indicative of a transition to crazing was not found consistent with nanotubes suppressing crazing in homopolymers. Scanning electron microscopy images of the fractured surfaces show agglomerates of carbon nanotubes present which are likely limiting the efficacy of carbon nanotubes at toughening the interface.
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- PAR ID:
- 10386056
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Polymer Engineering & Science
- Volume:
- 61
- Issue:
- 4
- ISSN:
- 0032-3888
- Format(s):
- Medium: X Size: p. 1186-1194
- Size(s):
- p. 1186-1194
- Sponsoring Org:
- National Science Foundation
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