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The moisture- and salt water-induced degradation of asphalt concrete molecular systems was investigated via molecular dynamics simulations. To establish the microstructure-to-property relationship of asphalt concrete mixture under hygroscopic aging, water molecules and sodium chloride (NaCl) ionic solutes were uniformly distributed in the binder or concentrated at the interface. The mechanical properties of the binder were slightly degraded by moisture and NaCl solutes. The viscosity of the binder decreased with distributed water, whereas it increased as the content of NaCl solute in the salt water increased. Moreover, the NaCl solutes promoted the hygroscopic eigenstrain of the asphalt binder. The interfacial properties between the binder and aggregate were not noticeably affected when moisture and NaCl solutes were uniformly distributed in the binder. While the moisture penetration into the interface was thermodynamically spontaneous when the amount of water was sufficient, the NaCl solutes in the water hindered the diffusion of moisture into the interface. Nonetheless, salt water penetrated into the interface seriously reduced the interfacial adhesion and the cohesive law in mode I and mode II decohesion than pure water. The condensation of penetrated salt water and the associated peeling mechanism of the interface were discussed to clarify the hygroelastic damage mechanism of the asphalt concrete mixture. • Degradation of hygroscopically aged asphalt concrete mixture was studied. • Moisture and Salt water resulted in hygroscopic swelling and remarkable change in viscosity of AAA-1 binder. • Penetration of water molecules in asphalt mixture was thermodynamically spontaneous and degraded the interface. • Dissolved NaCl mitigated the penetration of salt water while seriously deteriorated the interface in asphalt mixture. • Hygroelastic properties of binder and interface essential to constitutive modelling of asphalt mixture were determined. [ABSTRACT FROM AUTHOR]

• Hyperthermal erosion of nanocomposites by atomic oxygen and nitrogen molecule was compared for the first time. • Optimum reactive simulation condition to mimic disintegration under low earth orbital environment was provided. • Atomic oxygen bombardment showed reaction-assisted disintegration and desorption of nanocomposites. • Attack of nitrogen molecules showed comparable surface erosion to the atomic oxygen bombardment without active reaction. • Erosion yield of nanocomposites comparable to the in-flight experiment could be obtained. Against the hyperthermal atomic oxygen (AO) bombardment, mitigation of the surface recession has been the main issue in designing surface shielding materials in low earth orbital (LEO) environment. Meanwhile, the role of nitrogen molecules (N 2) in LEO and sub-LEO on disintegration of the shielding materials has rarely been studied despite their abundance and non-negligible colliding energy. This study for the first time compared the surface chemistry and disintegration of Kapton polyimide-based nanocomposites under AO and N 2 bombardment conditions using a reactive molecular dynamics (MD) simulation. The heat transfer from the surface to the behind layer and the associated boundary condition for the bombardment simulation were primarily discussed to provide the optimum bombardment simulation setup. Polyhedral oligomeric silsesquioxane (POSS), carbon nanotube (CNT) and graphene were respectively blended with Kapton to evaluate the damage mitigation efficacy. The addition of all types of additives to Kapton induced a notable thermo-protection effect. AO bombardment resulted in a sequential disintegration of oxidation and desorption, whereas the surface recession of nanocomposites by exposure to N 2 collision was mainly caused by physical desorption. It was also noteworthy that the surface recession caused by N 2 bombardment was comparable to that by AO attack at the same fluence. [Display omitted]. [ABSTRACT FROM AUTHOR]

Low-dimensional nanocarbon reinforcements in multifunctional composites have neither defect-free conjugate structures nor efficient interfacial properties in general. Moreover, synthesizing polymer nanocomposites involves intrinsic and extrinsic structural defects, which undoubtedly degrade the properties of the nanocarbons. However, several advantages and even useful applications of such structural defects have pioneered the defect engineering of nanocarbon structures. Here, we assessed the reciprocity of the degradation of single-layer graphene and the tailoring of the interfacial load transfer by structural defects. For this purpose, we used a molecular dynamics simulation and its hierarchical bridging to a mean-field micro-mechanics model for linear elastic behavior. Crystallographic defects and oxygen functionalization were considered the representative intrinsic and extrinsic defects, respectively. Despite the notably degraded elasticity of the nanocomposites involving direct load bearing by the defected graphene, those readily governed by the interfacial load transfer were significantly improved. The contributions of both types of defects to the interface were verified using the local stress concentration on the embedded graphene during the mechanical loading of nanocomposites and an additional mode I and II decohesion test. Lastly, the critical aspect ratio of graphene that maximizes the effects of the defects on the interface stiffness of the nanocomposites was derived for defect engineering. [Display omitted] • Oxygen functional group and TSW defect degrade mechanical properties of graphenes. • Interfacial load transfer and associated elastic modulus of nanocomposites were promoted by structural defect. • Cohesive law between defected graphene and PET matrix was correlated to the surface roughness of graphenes. • Reciprocity of interface and elasticity of defected graphene was studied by micromechanics model. • Critical aspect ratio of graphene to take advantage of defect was defined for defect engineering. [ABSTRACT FROM AUTHOR]