Large pore size nanoporous materials from the self-assembly of asymmetric bottlebrush block copolymers

Asymmetric polystyrene-polylactide (PS-PLA) bottlebrush block copolymers have been shown to self-assemble into a cylindrical morphology with large domain spacings. PLA cylinders can be selectively etched out of the shear-aligned polymer monoliths to generate nanoporous materials with an average cylindrical pore diameter of 55 nm. The remaining bottlebrush backbone provides a functional, hydrophilic coating inside the nanopores. This methodology significantly expands the range of pore sizes attainable in block copolymer based nanoporous materials.     

Strength modeling of brittle materials with two- and three-dimensional pore structures

Strength under compression of highly porous aerated autoclaved concrete was modeled by means of Finite Element Analysis of the porous microstructure. The complex microstructure of aerated autoclaved concrete is characterized by three hierarchical levels of pores. Strength and failure behaviour is controlled by large artificial air pores (AAP) with a mean diameter of 0.5–3 mm. Stress distribution in the brittle matrix material under external load was calculated by FEA for different pore arrangements. Based on the stress distribution multiaxial Weibull Theory was used to predict failure probability with regard to the porous microstructure. Two- and three-dimensional ordered pore arrangements show an exponential decrease of strength with porosity in the range of 0–0.4, depending on the Weibull parameter m of the matrix material. Strength vs. porosity relation differs significantly for pore structures with simple cubic and body centered cubic pore arrangements. The compatibility of two-dimensional with three-dimensional models is examined.     

Characterisation methods for functionally graded materials

In this paper the characterisation of functionally graded materials is elucidated by several different methods. These methods described here are used for the quantitative analysis of materials with a local dependence of microstructure parameters. Using X-ray microscopy (computed tomography) for 3D-measurements and optical microscopy on polished sections for 1D and 2D measurements on the same sample, a ceramic filter consisting of sintered spherical particles, various mathematical evaluation methods are described and compared.     

Characterisation of bubble materials

The rapid development of magnetic bubble technology has required growth to exacting specifications of a large number of magnetic films of garnets and some amorphous binary and ternary alloys of rare-earth and transition metals. The characterisation of these films is an essential part in the search for newer materials which hold out promise for better device performance and cost viability. Many methods of films characterisation have been reported from time to time. By and large, these methods can be divided into two groups: one, bulk measurements made on the film and two, measurements made on the domains. We have attempted to collate and briefly introduce various techniques to characterise magnetic bubble materials in this review.     

纳米多孔薄膜孔结构的非破坏性表征

对纳米多孔低介电常数薄膜孔洞率、孔径、孔径分布和孔洞连通性等孔结构的表征有助于理解薄膜的结构和提高其性能。近年来开展了利用与特殊X射线反射联用的小角中子散射、小角X 射线散射、椭偏测孔仪、正电子湮没谱和表面声波谱等非破坏性方法表征多孔低介电常数薄膜孔结构的研究。介绍了这些方法的基本原理,综述了利用这些方法研究低介电常数介质薄膜及其集成工艺的进展,总结了这些方法表征多孔薄膜孔结构的特征。     

Controlled nanoporous structures of a marine diatom

We demonstrated chemical etching of a marine diatom shell with 1 N NaOH for controlling the pore size of nanoporous structures of the shell under various conditions. Scanning electron microscopy (SEM) images clearly revealed that the pore size of the diatom shells was regulated in the case of etching at 25 degrees C. In contrast, fluctuations in the etched structures was relatively high even during short periods degradation at 40, 60, and 90 degrees C; therefore, controlled nanoporous structures could not be fabricated. This is the first example of artificial modification of natural diatom shells at the nanoscale although diatom shells have been widely used in industry. In addition, a backbone-like structure was observed during the etching process. The structure was similar to the intermediate structure observed during the primitive stage of the diatom cell growth. Probably, this information is valuable for studying the mechanism of nanoporous structures of diatoms.     

Predicting the structure of screw dislocations in nanoporous materials

Extended microscale crystal defects, including dislocations and stacking faults, can radically alter the properties of technologically important materials. Determining the atomic structure and the influence of defects on properties remains a major experimental and computational challenge. Using a newly developed simulation technique, the structure of the 1/2a <100> screw dislocation in nanoporous zeolite A has been modelled. The predicted channel structure has a spiral form that resembles a nanoscale corkscrew. Our findings suggest that the dislocation will enhance the transport of molecules from the surface to the interior of the crystal while retarding transport parallel to the surface. Crucially, the dislocation creates an activated, locally chiral environment that may have enantioselective applications. These predictions highlight the influence that microscale defects have on the properties of structurally complex materials, in addition to their pivotal role in crystal growth.     

Synthesis and characterization of Y2O3:Er3+ upconversion materials with nanoporous structures

Y2O3:Er3+ upconversion materials with nanoporous structures were prepared by a hydrothermal method following a post-thermal treatment. The structure and morphology of the materials were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results indicated that the as-obtained Y2O3:Er3+ powders were of cubic-phase structure, and the nanoporous structure was formed in the annealing process. The optical results indicated that high annealing temperature could improve the upconversion properties, but it could destroy the nanoporous structure. Under 980 nm excitation, red (4F(9/2) --> 4I(15/2) and green (2H(11/2), 4S(3/2) --> 4I(15/2)) upconversion luminescence was observed. The studies on the intensity dependence of upconversion emission indicated that two-photon processes were responsible for the green and red upconversion luminescence. This kind of multifunctional material has potential applications in nanocontainers for use as biomolecule and drugs carriers.     

Fluorinated and nanoporous graphene materials as sorbents for gas separations

The physisorption of gases on surfaces depends on the electrostatic and dispersion interactions with adsorbates. The former can be tuned by introducing charge variations in the material, and the latter can be tuned by chemical substitution. Using atomistic Monte Carlo calculations, the Henry's law constants, and isosteric heats of adsorption of CH(4), CO(2), N(2), O(2), H(2)S, SO(2), and H(2)O on graphene, two-dimensional polyphenylene (2D-PP), fluorographene, and fluoro(2D-PP) surfaces are used to demonstrate the tunability of these two types of interaction. With the exception of H(2)O, fluorination and nanoporosity-induced charge variations reduce the binding of the adsorbates. Gas separations relevant for CO(2) sequestration, biogas upgrading, SO(2) pollution control, and air dehumidification are considered, and in most cases, the nanoporosity and fluorination reduce the selectivity of adsorption. The exceptions are separations involving adsorption of H(2)O and the SO(2)/N(2) separation, where the large dipole moments of the adsorbed species leads to enhanced binding relative to the nonpolar species.     

Characterisation of heat spreader materials for pulsed IGBT operation

Insulated gate bipolar transistors (IGBTs) have a very high output power and generate correspondingly large amounts of heat. If not dissipated efficiently, this heat will destroy the IC (integrated circuit). Furthermore, since the input to the IGBT is often in the form of a pulsed wave, the rapid repeated heating and cooling of the chip and the surrounding packaging cause physical stresses, which in turn eventually lead to delamination and breakdown. Reducing the magnitude of thermal excursion in pulsed mode operations reduces the amount of stress caused by expansion and contraction, thereby reducing delamination and maintaining component efficiency for a longer period of time. It is therefore important to maintain a low rate of thermal expansion, or have a slow enough change in temperature for the physical stresses not to be damaging. This is normally done with heat sink assemblies, which form an integral part of IGBT design. This study investigates, via simulations using the transmission line matrix method, the thermal responses of some of the popular heat spreader materials. Material combinations within the layered structure of the heat sink assembly will give different thermal responses, and thus an analysis of operational behaviour of these components, with attention given to the input frequency as well as duty cycle, would provide a better guide to designing more suitable and efficient packaging assemblies and heat sinks     

Characterisation of impact damage in skin-stringer composite structures

In studies aimed at understanding the impact performance of structures made from carbon-fibre composites, effects of structural geometry, material type and impact location have been investigated in skin-stringer panels representative of aircraft structure. Effects were investigated for low-velocity impacts to the skin in the bay between stringers, over a stringer foot, and over a stringer centreline. Detailed studies of the impact damage at these locations were investigated using ultrasonic techniques, and optical and electron microscopy. The damage characteristics were explained in terms of the proportion of energy absorbed through damage, such as delamination, and elastic effects, such as structural response of the panel.     

Characterisation of bimodal grain structures in HSLA steels

High strength low alloy (HSLA) steels can show varying degrees of bimodality in their grain size distributions following rolling and also in the reheated condition, which can have significant effects on their toughness. Current methods of measuring bimodality work well for distinguishing between structures with significantly different levels and/or types of bimodality. However, these are not as good at consistently quantifying small differences between microstructures of, for example, steels processed under different conditions. This paper suggests a new method to construct the grain size distributions (in area-percent versus linear scale of equivalent circle diameter grain size) and to quantify bimodality in HSLA steels based on two parameters (peak height ratio, PHR, and peak grain size range, PGSR) measured from such distributions. The parameters were found to be simple, easy to measure, less subjective and more consistent for these steels compared to the standard and non-standard parameters used in the literature.     

CO2捕集用具有多级孔结构纳米孔炭的制备（英文）

以模板法结合化学活化法制备了具有分级结构的纳米孔炭。分别利用氮气吸附法和热重分析法考查KOH活化程度对模板法制备中孔炭的孔结构的影响和不同孔结构的多孔炭对CO2的吸附性能。结果表明,KOH活化不仅增加了大量的微孔,而且使得模板脱除得到的中孔数量降低。中孔吸附CO2对孔表面的利用率最高,而中孔和微孔的合适配比更有利用综合提高CO2的吸附量。制备的纳米孔炭具有较高的CO2吸附量和较好的循环性能和稳定性。     

Characterisation of pore structure by combining mercury porosimetry and micrography

Savonnières, a French layered oolithic limestone, shows important ink-bottle effects. As a consequence, a great discrepancy is observed between the results of different techniques to determine the pore volume distribution. It is shown that mercury intrusion porosimetry results can be considered as the main drainage curve and are, for this kind of materials, not convenient to determine the apparent pore volume distribution due to hysteresis phenomena. The main wetting curve is obtained using image analysing techniques on SEM-micrographs, combined with pressure membrane apparatus results on capillary saturated samples. A simple structural hysteresis model is developed to predict the mercury intrusion porosimetry results, starting from the main wetting curve. The good agreement between theory and experiment verifies that the large difference between main wetting and main drainage curve can indeed be attributed to structural hysteresis. In this way, the presented technique gives, in addition to a better knowledge of the pore volume distribution, insight in the pore geometry and connectivity, which can serve as input for microstructure-based transport models.     

Calculation of mean pore size in porous materials

A method is proposed for calculating the narrowest cross sections of pore channels averaged over the filtration surface. The calculated results are confirmed by experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 4, pp. 607–611, October, 1987.     

Surface effects on the mechanical properties of nanoporous materials

Using the theory of surface elasticity, we investigate the mechanical properties of nanoporous materials. The classical theory of porous materials is modified to account for surface effects, which become increasingly important as the characteristic sizes of microstructures shrink to nanometers. First, a refined Timoshenko beam model is presented to predict the effective elastic modulus of nanoporous materials. Then the surface effects on the elastic microstructural buckling behavior of nanoporous materials are examined. In particular, nanoporous gold is taken as an example to illustrate the application of the proposed model. The results reveal that both the elastic modulus and the critical buckling behavior of nanoporous materials exhibit a distinct dependence on the characteristic sizes of microstructures, e.g. the average ligament width.