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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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Interfacial cavitation
Abstract Cavitation has long been recognized as a crucial predictor, or precursor, to the ultimate failure of various materials, ranging from ductile metals to soft and biological materials. Traditionally, cavitation in solids is defined as an unstable expansion of a void or a defect within a material. The critical applied load needed to trigger this instability -- the critical pressure -- is a lengthscale independent material property and has been predicted by numerous theoretical studies for a breadth of constitutive models. While these studies usually assume that cavitation initiates from defects in the bulk of an otherwise homogeneous medium, an alternative and potentially more ubiquitous scenario can occur if the defects are found at interfaces between two distinct media within the body. Such interfaces are becoming increasingly common in modern materials with the use of multimaterial composites and layer-by-layer additive manufacturing methods. However, a criterion to determine the threshold for interfacial failure, in analogy to the bulk cavitation limit, has yet to be reported. In this work, we fill this gap. Our theoretical model captures a lengthscale independent limit for interfacial cavitation, and is shown to agree with our observations at two distinct lengthscales, via two different experimental systems. To further understand the competition between the two cavitation modes (bulk versus interface), we expand our investigation beyond the elastic response to understand the ensuing unstable propagation of delamination at the interface. A phase diagram summarizes these results, showing regimes in which interfacial failure becomes the dominant mechanism.
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- Award ID(s):
- 1942016
- PAR ID:
- 10377654
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- PNAS Nexus
- Volume:
- 1
- Issue:
- 4
- ISSN:
- 2752-6542
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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