Molecular Dynamics Simulation of the Structure and Hydroxylation of Silica Glass Surfaces

The surface structure of silica glasses has been simulated using molecular dynamics. The surface hydroxyl concentration was estimated to be 4.5/nm², based on surface defect statistics. Hydroxyl-silica potentials were developed and used to study the hydroxylation of silica surface. It is found that the energy of chemisorption of water declines in the sequence: three coordinated silicon (Si³) and non-bridging oxygen (NBO) on separate sites, Si³ and NBO on combined sites, two- and three-membered rings. Partial hydroxylation of the most reactive sites, which leads to an OH coverage of 2.5/nm², was studied. Structural relaxation after hydroxylation was observed.     

Epitaxy growth and directed crystallization of high-density polyethylene in the oriented blends with isotactic polypropylene

Various lamellar orientations of high-density polyethylene (HDPE), due to competition between bulk nucleation and interfacial nucleation, have been realized in its melt drawn blends with isotactic polypropylene (iPP) upon cooling after subjected to 160 °C for 30 min. Directed crystallization, with heterogeneous nucleation in the bulk (within domains), is defined as lamellar growth along boundary of anisotropic domains and is favored in larger domains at higher temperature (slow cooling), since overgrowth of lamellae can feel the interface rather than impingement with neighbor ones as a result of scare nuclei at higher temperature. Moreover, lamellar growth caused by directed crystallization is dependent of dimension of confinement. Due to 2D confinement of cylindrical domains, lamellae can only grow along the axis of cylinder and thus b-axis orientation is formed. While in the layered domains with 1D confinement, however, lamellae grow with the normal of (110) plane along the melt drawn direction. On the other hand, epitaxial growth of HDPE chains onto iPP lamellae is related to the surface-induced crystallization and dominated by the interfacial nucleation. Only interfacial nucleation is preferred can epitaxial growth occur. Therefore, retarded crystallization, realized by either strong confinement in finer domains or rapid cooling or both, is favorable for it.     

管材专用PPR的等温结晶动力学

研究了管材专用无规共聚聚丙烯(PPR)的结晶温度和等温结晶行为,利用Avrami方程对等温结晶过程和动力学进行了分析。结果表明:北欧化工公司的PPR1具有更高的结晶温度、结晶度以及更快的结晶速率。同一结晶温度条件下,国产PPR3的结晶度达到一半的时间略高于其他PPR。利用Hoffman-Lauritzen结晶动力学理论计算得到了PPR的成核常数和结晶生长时大分子在垂直于分子链方向的折叠表面自由能(σ_e),与其他试样相比,PPR1的σ_e最低,PPR3的σ_e最高,结晶速率最慢。通过偏光显微镜照片可以发现,PPR1的球晶尺寸最小,PPR3和PPR4的球晶较大,球晶尺寸比较接近。     

硅片基底表面修饰及浸润性变化

固体表面的浸润性是自然界普遍存在的一种性质,在人们的日常生活、工业和农业中具有重要的作用.液体对在固体界面的浸润行为源于固体的表面能和微纳米结构.基于自然界生物的浸润行为,人们对特殊浸润性的功能表面产生了极大地兴趣.近几年来,有关特殊浸润性表面的研究取得了不错的进展.在此,我们讨论了硅片基底表面修饰及其浸润性的变化.通...     

Vinyl-functionalized polyborosiloxane for improving mechanical and flame-retardancy performances of silicone rubber foam composites

In this work, we first synthesized vinyl-terminated polyborosiloxane (pBS) filler, and then incorporated it into silicone rubber foam (SRF) matrix to prepare composite materials through a simple chemical dehydrogenative foaming method under ambient conditions. The pBS filler with reactive groups could form physical and chemical crosslinking networks in SRF, leading to an excellent dispersion level of pBS in the SRF matrix. Moreover, the inserted pBS could remarkably improve the mechanical and flame-retardancy properties of SRF-pBS composites. Intriguingly, the SRF-pBS6 foam containing 6 wt% of pBS possessed a uniform porous structure and balanced mechanical properties (σ_b = 65.4 kPa, ε_b = 56.7%, compression stress 97.1 kPa), thermal conductivity (0.102 W (m K)^?1), limiting oxygen index (29.8%) and UL-94 rating (V-0) among the prepared foams. In addition, the incorporated pBS (6 wt%) could synergistically catalyze the formation of a silicon–boron strengthened ceramic-like protective layer under fire and was capable of suppressing heat and smoke production in the SRF-pBS6 foam. The present work provides a promising way for developing high mechanical and flame-retardant polymeric foam materials with good thermal insulation. © 2021 Society of Industrial Chemistry.     

Establishment of a color tolerance for yarn-dyed fabrics from different color-depth yarns

Yarn-dyed fabric is often woven from warp and weft yarns in the same color depth to ensure a uniform color appearance. The difference in color depth between warp and weft tends to result in the uneven color of the yarn-dyed fabric. This article aims to establish a color tolerance for yarn-dyed fabric that can be woven with a qualified color appearance but from the warp and weft yarns in different color depths. A total of 27 yarn-dyed fabric samples in three color series (red, yellow, and blue) were evaluated by using the yarn-dyed fabric from warp and weft yarns in the same color depth of 2% (on weight of fabric, owf) as the standard. Visual assessment and instrumental measurement of color were carried out to establish the color tolerance ellipse that was defined as CMC (Color Measurement Committee) color differences (2:1) of no more than 1.00. It was found that the color strengths (K/S) and color differences (ΔE_CMC(2:1)) of these fabric samples for each color series had linear relationships with the color depths of warp and weft yarns. The color tolerance ellipses indicated that, even though the warp and weft yarns had an apparent color difference, they could be woven in fabrics with relatively uniform color appearance and meet the requirements for yarn-dyed fabric. This work provided valuable insight into the production of qualified yarn-dyed fabrics from unqualified dyed yarns.     

Determination of interfacial tension and viscosity under dripping flow in a step T-junction microdevice

Microfluidic approaches for the determination of interfacial tension and viscosity of liquid-liquid systems still face some challenges. One of them is liquid-liquid systems with low interfacial and high viscosity, because dripping flow in normal microdevices can't be easily realized for the systems. In this work, we designed a capillary embedded step T-junction microdevice to develop a modified microfluidic approach to determine the interfacial tension of several systems, specially, for the systems with low interfacial tension and high viscosity. This method combines a classical T-junction geometry with a step to strengthen the shear force further to form monodispersed water/oil (w/o) or aqueous two-phase (ATP) droplet under dripping flow. For systems with low interfacial tension and high viscosity, the operating range for dripping flow is relative narrow whereas a wider dripping flow operating range can be realized in this step T-junction microdevice when the capillary number of the continuous phase is in the range of 0.01 to 0.7. Additionally, the viscosity of the continuous phase was also measured in the same microdevice. Several different systems with an interfacial tension from 1.0 to 8.0 mN·m^-1 and a viscosity from 0.9 to 10 mPa·s were measured accurately. The experimental results are in good agreement with the data obtained from a commercial interfacial tensiometer and a spinning digital viscometer. This work could extend the application of microfluidic flows.     

Insights into the confinement effect on isobutane alkylation with C4 olefin catalyzed by zeolite catalyst: A combined theoretical and experimental study

Elucidating the confinement effect harbours tremendous significance for isobutane alkylation with C₄ olefin. Herein, the confinement effect over zeolite catalysts was elucidated by combining DFT calculations, experiments(using the novel Beta zeolite exposing only external surfaces(Beta-E) and conventional Beta-I zeolite with both external and internal surfaces) and multi-techniques(e.g., TGA-DTG,HRTEM, SEM and XRD). It is found that the main active sites for C₄ alkylation r...     

骨料线机制砂库装车系统干法除尘设计

本文通过对现有骨料线机制砂库装车除尘系统的介绍,探讨了干法除尘设计的基本思路和具体的工艺过程。结果表明,通过设计带气力输送系统的除尘工艺。能够很好的解决现有工艺的不足,能够提高骨料企业的环境治理水平、具有很好的参考价值。     

Aqueous-based,high-density nanoporous carbon xerogels with high specific surface area for supercapacitors

Journal of Porous Materials - Electrode materials with high density for assembling supercapacitors with high volumetric capacitance are urgently needed. Herein, nanoporous carbon xerogels (NPCXs)...