Insights into Mechanical Dynamics of Nanoscale Interfaces in Epoxy Composites Using Nanorheology Atomic Force Microscopy

Abstract

Interfacial polymer layers with nanoscale size play critical roles in dissipating the strain energy around cracks and defects in structural nanocomposites, thereby enhancing the material's fracture toughness. However, understanding how the intrinsic mechanical dynamics of the interfacial layer determine the toughening and reinforcement mechanisms in various polymer nanocomposites remains a major challenge. Here, by means of a recently developed nanorheology atomic force microscopy method, also known as nanoscale dynamic mechanical analysis (nDMA), we report direct mapping of dynamic mechanical responses at the interface of a model epoxy nanocomposite under the transition from a glassy to a rubbery state. We demonstrate a significant deviation in the dynamic moduli of the interface from matrix behavior. Interestingly, the sign of the deviation is observed to be reversed when the polymer changes from a glassy to a rubbery state, which provides an excellent explanation for the difference in the modulus reinforcement between glassy and rubbery epoxy nanocomposites. More importantly, nDMA loss tangent images unambiguously show an enhanced viscoelastic response at the interface compared to the bulk matrix in the glassy state. This observation can therefore provide important insights into the nanoscale toughening mechanism that occurs in epoxy nanocomposites due to viscoelastic energy dissipation at the interface.

Atomistic Modeling of the Effect of Temperature on Interfacial Properties of 3D-Printed Continuous Carbon Fiber-Reinforced Polyamide 6 Composite: From Processing to Loading

“…Nanoscale properties are necessary for mesoscale and macroscale modeling. Unfortunately, advanced nanoscale experimental techniques, such as atomic force microscopy, − nanoindentation testing, − and nanoscale Fourier transform infrared spectroscopy, , are only able to measure interfacial properties at the nanoscale, not the dynamic evolution of interfaces. Thus, MD simulations are possibly the only effective tool at this point in time that can study the dynamic evolution of interfaces and the factors that affect this evolution.…”

Electronic Interaction of Epoxy Resin with Copper at the Adhered Interface

“…The adhesive technology used for assembling two dissimilar materials is widely adopted in various industries, including automotive, aerospace, construction, electronics, and healthcare. − One of the most common thermosetting adhesives is a class of epoxy resins, composed of an epoxy base and a hardener such as amine groups. − The resin solidifies on an adherend through curing reactions, forming an interface with the adherend. Mechanical properties of the resin are closely related to the resultant network structure formed by the curing reactions in the bulk − as well as at the interface. − As some interfacial events dominate the adhesion phenomena, it is crucial to better understand what kinds of interactions at the interface contribute to the adhesive strength from both theoretical and experimental perspectives.…”

“…Mechanical properties of the resin are closely related to the resultant network structure formed by the curing reactions in the bulk 7 − 11 as well as at the interface. 12 − 14 As some interfacial events dominate the adhesion phenomena, it is crucial to better understand what kinds of interactions at the interface contribute to the adhesive strength from both theoretical and experimental perspectives.…”

Effect of Condensed Water at an Alumina/Epoxy Resin Interface on Curing Reaction

“…Furthermore, it is known that the thickness of the water layer on the alumina surface varies with the relative humidity . On the other hand, epoxy resins , are typical thermosetting polymers characterized by a three-dimensional network structure formed through polymerization and cross-linking reactions involving an epoxy base and a curing agent, such as amine. , While epoxy resins exhibit high durability, , they undergo deterioration due to water absorption over a long period of time. − The degradation mechanism, such as the protonation of amino groups in the presence of water, has also been studied. , It is important to understand the behavior of condensed water molecules at the alumina/epoxy interface when considering adhesion and degradation. − …”

“… 17 , 18 It is important to understand the behavior of condensed water molecules at the alumina/epoxy interface when considering adhesion and degradation. 19 − 21 …”