No abstract

Coal‐based environment‐friendly PVC/ASA flame‐retardant and antistatic composites were made by melt blending poly(vinyl chloride)/acrylonitrile–styrene‐acrylate (PVC/ASA) with self‐made alkaline calcium‐based coal gangue thermal stabilizer (Y‐CG) and dimethyl sulfoxide (DMSO) intercalation modified Coal (A‐Coal). The flame‐retardant mechanism of PVC/ASA/A‐Coal/Y‐CG composites was due to incombustible gas, maze effect, carbon residue layer and blowing‐out effect through limiting oxygen index (LOI), vertical combustion (UL‐94) and scanning electron microscope (SEM) test. The results indicated that PVC/ASA/12A‐Coal/10Y‐CG composites had the best flame‐retardant properties with LOI value of 31.8% and can pass the V‐0 rating in the UL‐94 test. After combustion, PVC/ASA/12A‐Coal/10Y‐CG composites formed a dense carbon layer that inhibits gas released and heat transferred. The surface resistivity (ρs) and volume resistivity (ρv) of PVC/ASA/A‐Coal/Y‐CG composites first decreased and then increased with the increase of A‐Coal content. The ρs and ρv values of PVC/ASA/12A‐Coal/10Y‐CG composites decreased to the minimum values of 5.14 × 106 Ω and 9.05 × 105 Ω·cm. The tensile strength and impact strength of PVC/ASA/A‐Coal/Y‐CG composites first increased and then decreased with A‐Coal content. The tensile strength and impact strength of PVC/ASA/12A‐Coal/10Y‐CG composites reached the maximum of 65.03 MPa and 17.52 kJ/m2, respectively. To sum up, the incorporation of A‐Coal and Y‐CG can reinforce and toughen PVC/ASA composites, but it can also enhance their flame‐retardant, antistatic properties.

The segmental joints are the weak parts of the immersed tunnel structure, and their deformation characteristics are closely correlated with the waterproof behavior and structural safety of the whole tunnel. In order to study the deformation characteristics of the segmental joints of immersed structure, in this paper, the E13 pipe section in the natural foundation section of an immersed tunnel in the Hong Kong-Zhuhai-Macao Bridge is taken as the research object, and the model test of the immersed tunnel is carried out. The similarity ratio of the model to the prototype is determined according to the actual engineering scale and the capability of the model test system, and the plexiglass is selected as the model material of the immersed tunnel according to the similarity of elastic modulus and density. In the test, various working conditions, including back-silting load and different prestress control values, are analyzed, and the influence of settlement and opening of the immersed tunnel is obtained, along with the stress-strain characteristics of the segment joints. Results show that the increase of the back-silting load will increase the element settlement and the expansion of the segment joints, but the application of prestress increases the overall stiffness of the element, which can effectively restrain the settlement of element and the expansion of joints. Furthermore, based on the model test conditions, a finite element model is established to simulate the mechanical behavior of the immersed tunnel. The settlement curve and stress-strain curve of the numerical analysis are found to be similar to those obtained from the model test, which verifies the reliability of the model test.

The coalescence of nanodroplets is an important interfacial phenomenon and is the key to many real-world applications. However, the microscopic mechanism for this process remains unclear. In this work, we propose a time-dependent density functional theory (TDDFT) to understand and predict this process. The formation of a "peanut" nanodroplet seems key to the coalescence process, before and after which the system is dominated by a nucleation mechanism and an ordinary diffusion mechanism, respectively. It appears that molecular attraction is not only the driving force but also the resistance of droplet coalescence. The velocity distribution indicates that there is a significant mass transfer on the vapor-liquid interphase. During coalescence, there is a clear linear correlation between the free energy and the surface area of the vapor-liquid interface, which means surface tension is the dominant contribution to the free energy.

No abstract