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• Twisting causes tensile strength loss in CNT bundles while mitigating the inter-tube slipping performances. • Pull-out forces of inter-tubes increase with the elevation of the twisting level. • Outer-layer CNTs are more sensitive to twisting than inner-layer CNTs. • Decreased inter-tube distances due to twisting result in increasing vdW repulsion and adverse effects on the CNT bundle. The exceptional mechanical properties of carbon nanotubes (CNTs) have encouraged the development of high-performance synthetic fibers in composite materials. To understand the effect of twisting on the mechanical and slipping performances of CNT bundles, molecular dynamics simulation is applied to investigate the tensile performances, failure modes, and pull-out responses of twisted CNT bundles. A molecular model comprising nineteen parallel aligned single-walled carbon nanotubes (SWCNTs) is twisted into bundles at angles of 0°, 10°, and 20°, and further tensile and pull-out simulations are performed. The tensile simulation indicates that compared with the non-twisted CNT bundle showing a tensile strength of about 82 GPa with obvious inter-tube slipping, the 10°-twisted bundle exhibits a tensile strength of approximately 70 GPa with SWCNTs fracture as the main failure mode, which indicates that twisting improves the inter-tube slipping performance without causing excessive strength reduction. Comparatively, when the twisting angle is 20°, no inter-tube slipping is observed and the tensile strength of the CNT bundle is measured to be 55 GPa, which decreases by approximately 32.9 %. The pull-out simulations further reveal that the pull-out forces increase as the twisting angle increases and the weakened bundle strength of twisted bundle is attributed to the repulsive van der Waals forces caused by the reduced distances between inter-tubes. Essentially, twisting is unfavorable for the overall mechanical strength while torsional densification mitigates the inter-tube slipping, which indicates that a trade-off need to be achieved. This paper provides insights into the tensile and slipping performances of twisted CNT bundles and forms a basis for enhancing the assembled CNTs bundle as the next-generation reinforcing phase in composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular modeling and simulation of fiber/matrix interface are introduced. • Mechanical and adhesion properties of molecular interfaces are presented. • Interfacial degradations under environmental and loading conditions are discussed. • Underlying mechanisms of interfacial degradations are revealed. • Challenges and recommendations for future interfacial investigations are proposed. Fiber-reinforced polymer composites have been increasingly applied as reinforcing and load-bearing components in building constructions and civil infrastructures. Long-term exposure to changing environmental and loading conditions leads to composite degradation, which is highly related to degraded structure and properties of fiber/matrix interface and consequent interfacial debonding between fiber and matrix at nanoscale. By simulating interfacial structure and interactions with atomistic precision, molecular simulation allows for a high fidelity to interfacial variations as affected by environmental and loading conditions. In this paper, molecular investigations of interfacial degradation between fiber and matrix under various environmental and loading conditions are reviewed. Model construction of interfaces formed by different fibers and matrixes and simulation of various environmental and loading conditions are firstly introduced. Afterwards, mechanical and adhesion properties of molecular interfaces obtained from deformation simulations are presented. Meanwhile, interfacial degradations under various environmental and loading conditions are discussed and underlying mechanisms are revealed. Further discussions on modeling and simulation of molecular interface are proposed for future investigations. Overall, this work reviews previous molecular investigations of interfacial degradation of composites under different environmental and loading conditions, which contributes to evaluation of interfacial behaviors of composite materials during long-term service life. [ABSTRACT FROM AUTHOR]

Vinylester resin is widely used as matrix for fabricating glass fiber reinforced polymer in marine applications. Even though vinylester based material is understood to be durable in general, the interface between vinylester and the bonded additive can be degraded when subjected to various environmental conditions. Here, the degradation at vinylester/glass interface in chloride environment under elevated temperature is studied through molecular dynamics simulations. The atomistic model consists of a cross-linked vinylester matrix and an amorphous silica substrate. The results show that environmental condition of chloride and elevated temperature leads to the largest loss of interfacial adhesion, which correlates with structural and mechanical degradation of bonded interface. The degradation mechanism is indicated by reduced interfacial stress, decreased vinylester density close to interface, and formation of H-bond. Softened polymer matrix and deteriorated interface inhibit the stress transfer between fiber and matrix, eventually leading to deteriorated macroscopic properties. The performance of degraded vinylester is also compared with other polymer matrixes to provide guidance for designing more durable polymeric composites. This study provides fundamental information on interfacial deterioration in vinylester based composites, which forms the basis for predicting degradation of macroscopic performance. [Display omitted] • An atomistic simulation framework to study the deterioration of vinyl ester based composites is proposed. • Hygrothermal and chloride environment inhibits the stress transfer between fiber and matrix. • Local interfacial deterioration causes the deteriorated fiber/matrix bond under chloride and elevated temperature. • The hydrophilicity of hydroxylated silica surface aggravates the interfacial degradation. • Water-swellable layer of vinyl ester near the fiber surface in chloride environment promotes the interfacial mismatches. [ABSTRACT FROM AUTHOR]

The degradation at the glass fiber/matrix interface through molecular dynamics simulations in hygrothermal environment is investigated. The glass fiber reinforced polymer composite has been modeled using a cross-linked epoxy matrix and amorphous silica substrate. The degradation mechanism in hygrothermal environment is indicated through the reduction of decreased adhesion energy and the weakened intermolecular interactions with the consideration of hydration bond. Furthermore, softened epoxy molecules in hygrothermal conditioning possess a lower density near the fiber surface, which inhabits the stress transfer between fiber and matrix, eventually leading to the deteriorated interfacial adhesion. Our simulation results echo with the experimental measurements, which can be further calibrated and utilized as inputs in micromechanical models to bridge the gap between the macroscopic and microscopic behavior of civil infrastructures. Image 1 • An atomistic simulation framework to study the hygrothermal deterioration of polymer-matrix composites is proposed. • Local interfacial deterioration causes the deteriorated fiber/matrix bond in hygrothermal environment. • Hygrothermal environment reduces the adhesion energy at fiber/matrix interface. • The hydrophilicity of hydroxylated silica surface aggravates the interfacial degradation. • The water-swellable polymer inhibits the stress transfer and promotes the interfacial mismatches. [ABSTRACT FROM AUTHOR]

Due to the serious consequences of the accumulation of heavy metals in organisms throughout the aqueous phase, the treatment of heavy metal pollution has received extensive attention. Porous geopolymer adsorbent (PGA) has been proposed as a promising remover of heavy metal ions due to its production convenience, low cost, and large surface area. However, it is easy to be broken under water impact. Besides, compared to some other adsorbents, the heavy metal ions capacity of PGA needs to be enhanced. In this paper, PGA with 1000 kg/m3 density was directly prepared based on solid waste including fly ash and slag at room temperature. Nano-silica (NS) was added to improve material strength. The compressive strength of PGA with 2 % NS addition increases up to 63.5 % compared with the material without NS addition, and the removal rate of Cu2+ goes to 78.4 % under this condition. Although the filling effect caused by NS addition is not beneficial for the adsorption ability improvement, the molecular dynamics simulation results confirm that the physical adsorption ability upward is mainly caused by the more Natrium-Aluminate-Silicate-Hydrate formation due to the decreasing Ca/Si ratio. Compared with Calcium-Aluminate-Silicate-Hydrate, Natrium-Aluminate-Silicate-Hydrate has a higher physical adsorption ability due to the evenly distributed electropositive region known from the density functional theory analysis, which contributes to PGA adsorption capacity from the outside environment. [Display omitted] • Porous geopolymer adsorbent is a promising remover of heavy metal ions. • NS addition improves adsorbent strength by 63.5% avoiding the adsorbent from being broken. • NS addition leads to more NASH formation contributing to adsorption ability improvement. • The rate of Cu2+ removed by porous geopolymer adsorbent in this study reaches 78.4%. • The evenly distributed electropositive region of NASH contributes to a stronger adsorption ability. [ABSTRACT FROM AUTHOR]

An effective method to obtain white-light emitters by encapsulating a single lanthanide metal ion into an alkaline earth metal-organic coordination polymers is presented. Two novel complexes SrL(H 2 O) and BaL(DMF) (L = 1,1′,1′′-(benzene-1,3,5-triyl)tripiperidine-4-carboxylic acid) were synthesized, and lanthanide metal ions were encapsulated by coordination with their active sites. The CIE coordinates of the modified complexes are tuned along two separate trajectories by regulating the content of either Eu 3+ or Tb 3+ . The trajectories of the complexes containing Eu 3+ pass through the white region in the CIE diagram. Different from the traditional idea of overlaying three emission colors, white-light emission of the modified complexes is explored by encapsulating only Eu 3+ into the blue-light emission coordination polymers to decrease the number of unmanageable variables. Luminescence measurements show that the complexes can specifically identify Fe 3+ with almost complete emission quenching, which is not observed in the presence of other metal ions. [ABSTRACT FROM AUTHOR]