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A water-filtering architecture based on nanoporous membranes is proposed for water desalination. In this paper, we show via molecular dynamics simulations, a polymerized fullerite membrane enables an outstanding water permeability with perfect salt ion rejection. Compared to the conventional reverse osmosis and nanoporous graphene, the water permeability is found to be much higher. A collective motion of hoping single-file water through a nanopore, which is tuned through desalination velocity and temperature, is identified and proved to be of great significance in enhancing water permeability. Single-file water with concerted dipole orientation exhibits faster water permeation through nanopores of polymerized fullerite membrane. It is revealed that larger desalination velocity will bring defects to the dipole orientation of single-file water, resulting in water reorientation through nanopores and lower water permeability. The polymerized fullerite membrane is found to suffer from bending deformation at high hydraulic pressure, leading to pore enlargement and degradation of salt rejection. An optimization scheme is provided to ensure a sustainable desalination performance. These insights shed light on polymerized fullerite as a prospective membrane for water purification and provide theoretical guidelines for achieving fast water permeation through collection motion of single-file water.

One-dimensional diamond nanothread (DNT) has drawn intensive research interests and become a promising candidate for nanocomposites reinforcement. This paper explores the mechanical properties of DNT reinforced poly (methyl methacrylate) (PMMA) composite under tensile deformation via molecular dynamics simulation. The study shows that the Young's modulus and yielding stress of PMMA composite are enhanced by 85% and 15% with the incorporation of DNT. Remarkably, DNT which is a hydrogenated carbon nanotube (CNT) is proved to strengthen PMMA composite more effectively than CNT for a similar structure. The outstanding strengthening of DNT is attributed to interfacial interaction and mechanical interlocking between DNT and PMMA matrix. A pull-out simulation is conducted to examine the interfacial shear strength of DNT-PMMA interface and comparison studies are made with that of CNT-PMMA interface. The results reveal that DNT has higher load transference within PMMA composite than CNT, by presenting 34% above CNT in interfacial shear strength. It is also demonstrated that DNT morphology can significantly affect the interfacial interaction and mechanical interlocking with PMMA matrix, leading to distinguished reinforcement efficiency for PMMA composite. These findings will shed light to DNT application in nanocomposites and provide an important insight into reinforcing mechanism.

This paper investigates the microstructure evolution of CSA cement pastes with different water to cement ratios in various hydration stages. Microstructure information, such as porosity, cumulative and incremental pore volume of cement pastes, is revealed by the innovative non-contact electrical impedance measurement (NCEIM), low temperature differential scanning calorimetry (LT-DSC), nitrogen adsorption test and mercury intrusion porosimetry (MIP). The hydration features associated with microstructure evolution are identified by NCEIM, Micro-Raman spectra and heat evolution test. Through the overall analysis of experimental results, initial formation and evolution of microstructure of CSA cement pastes are identified.

Electrochemical impedance spectroscopy (EIS) is adopted as a nondestructive testing method for exploring the fracture feature of the carbon nanotube/cement composite materials. A novel equivalent circuit model is used to explain the change regularity of fracture toughness. Based on the charge transfer on the surface of carbon nanotubes (CNTs), the electrical resistance can be applied to evaluate the conducting efficiency in a certain orientation. The EIS results indicate that more CNTs fibers are perpendicular to the crack opening with increasing content of CNTs, which is corresponding with a higher fracture toughness of CNTs/cement composites. The experimental results also demonstrate the fracture toughness of CNTs/cement composites with different contents (0 wt%, 0.033 wt%, 0.066 wt% and 0.1 wt%) of CNTs could be accurately responded with linear relationship with the EIS results. Furthermore, an advanced equivalent circuit model is proposed to describe the impedance response of CNTs/cement composites. The EIS method therefore can be used as a reliable, convenient and non-destructive method to assess the fracture toughness of CNTs/cement composites.

Polymer matrixed nanocomposites commonly suffer from mechanical degradation when employed in a watery environment, but the destructive moisture effect and the impact of nano fillers lacks an integrated understanding. In this work, we investigate the water-induced defects of carbon nanotube (CNT) filled poly (methyl methacrylate) (PMMA) composite at the microscopic level. Three damage modes are detected and the corresponding damage mechanisms are verified to be involved in the microstructural evolution: i) hydrogen bonds tend to form efficiently between H2O and polymer atoms at the beginning of moisture absorption; ii) H2O aggregation in micro-pores induces polymer chain stretching and bulk volume expansion; iii) inconsistent response of CNT and polymer chains on water absorption dominates interfacial degradation. We find that CNTs plays a waterproofing role by reducing free volume and providing zigzagging diffusion paths for water molecules. This study discloses the mechanism of water-induced deterioration in nanocomposites, facilitating improvement of their underwater mechanical properties.

Diamond nanothread (DNT), a novel carbon-based nanomaterial exhibiting ultra-light density and outstanding mechanical properties, has attracted intensive attentions in polymer composites. This study investigates the influences of DNT on the glass transition temperature (Tg) of poly (methyl methacrylate) (PMMA) composites and reveals the glass-rubber transition mechanism through molecular dynamics simulation. We demonstrates that DNT exhibits better improvement than other carbon-based nanomaterials in enhancing the Tg of PMMA composite, suggesting that DNT is a promising reinforcement for polymer nanocomposite with higher service temperature and better mechanical performances. Significantly, we find that interfacial interactions including van der Waals interaction and mechanical interlocking play an important part in glass transition of PMMA composite. The transition from glassy state to rubbery is induced through the interfacial debonding brought by the enlargement of free volume at the interface. According to the interfacial degrading mechanism, cross links between DNT reinforcement and PMMA chains are introduced to provide bidirectional hindrance for free motions of polymer chains, resulting in a 70 K enhancement of Tg of PMMA composites. These findings not only shed light to the prospective application of DNT in advanced nanocomposite, but also provide important guidance to improve the reinforcing efficiency of nanomaterials in engineering application, such as building and aerospace industry.