Superfluidity of 4He Confined in a Porous Glass and Control of the Pore Size

⁴He confined in nanoporous media is one of the most interesting nano-sized systems. The aim of the present work is control of the pore size of nanoporous media in order to clarify the superfluid size effects. For the pore size control, monolayer adsorption of Kr on the pore wall is performed. The change in the pore size distribution by the monolayer adsorption are characterized by N₂ isotherms at 77 K. Superfluidity in the pores is observed with a torsional oscillator method. The pore diameter of the as-purchased Gelsil is estimated at 5.8 nm. The monolayer adsorption reduces the size by 1.1 nm, caused by the thickness of the Kr monolayer. The decrease in the pore size lowers the superfluid transition temperature by 40 mK.     

A method for manufacturing cellular metals with open- and close-type porosities

New approach for manufacturing metallic cellular materials with controlled open pore geometry and cells arrangement is presented. The method is based on the combination of rapid prototyping of a template with powder metallurgy. Modification of the procedure allows for additional introduction of closed-type porosity with pores smaller than those defined by the rapid prototyped template. The accuracy of the method for controlling the size, shape and arrangement of open-type pores is presented on the example of zinc with an inorganic template (CuSO₄). The same materials are used to produce a structure with two types of porosities combined in one structure, regular opened and irregular closed. The control of pore geometry allows for optimization of metallic cellular materials for their mechanical, chemical and biological applications.     

Nanospace engineering of KOH activated carbon

This paper demonstrates that nanospace engineering of KOH activated carbon is possible by controlling the degree of carbon consumption and metallic potassium intercalation into the carbon lattice during the activation process. High specific surface areas, porosities, sub-nanometer (<1 nm) and supra-nanometer (1-5 nm) pore volumes are quantitatively controlled by a combination of KOH concentration and activation temperature. The process typically leads to a bimodal pore size distribution, with a large, approximately constant number of sub-nanometer pores and a variable number of supra-nanometer pores. We show how to control the number of supra-nanometer pores in a manner not achieved previously by chemical activation. The chemical mechanism underlying this control is studied by following the evolution of elemental composition, specific surface area, porosity, and pore size distribution during KOH activation and preceding H(3)PO(4) activation. The oxygen, nitrogen, and hydrogen contents decrease during successive activation steps, creating a nanoporous carbon network with a porosity and surface area controllable for various applications, including gas storage. The formation of tunable sub-nanometer and supra-nanometer pores is validated by sub-critical nitrogen adsorption. Surface functional groups of KOH activated carbon are studied by microscopic infrared spectroscopy.     

Functionalized silicon membranes for selective bio-organism capture

Membranes with various pore size, length, morphology and density have been synthesized from diverse materials for size-exclusion-based separation. An example is the sterilization of intravenous lines by exclusion of bacteria and viruses using polyvinylidene fluoride membranes with 0.1-microm-diameter pores. Chemically specific filtration has recently been addressed for small molecules. Nevertheless, specific bio-organism immobilization and detection remains a great technical challenge in many biomedical applications, such as decontamination or analysis of air and liquids such as drinking water and body fluids. To achieve this goal, materials with controlled pore diameter, length and surface chemistry are required. In this letter, we present the first functionalized silicon membranes and demonstrate their ability to selectively capture simulated bio-organisms. These extremely versatile and rigid devices open the door to a new class of materials that are able to recognize the external fingerprints of bio-organisms-such as size and outer membrane proteins-for specific capture and detection applications.     

The fabrication of tunable nanoporous oxide surfaces by block copolymer lithography and atomic layer deposition

Patterned nanoscale materials with controllable characteristic feature sizes and periodicity are of considerable interest in a wide range of fields, with various possible applications ranging from biomedical to nanoelectronic devices. Block-copolymer (BC)-based lithography is a powerful tool for the fabrication of uniform, densely spaced nanometer-scale features over large areas. Following this bottom-up approach, nanoporous polymeric films can be deposited on any type of substrate. The nanoporous periodic template can be transferred to the underlying substrate by dry anisotropic etching. Nevertheless the physical sizes of the polymeric mask represent an important limitation in the implementation of suitable lithographic protocols based on BC technology, since the diameter and the center-to-center distance of the pores cannot be varied independently in this class of materials. This problem could be overcome by combining block copolymer technology with atomic layer deposition (ALD): by means of BC-based lithography a nanoporous SiO2 template, with well-reproducible characteristic dimensions, can be fabricated and subsequently used as a backbone for the growth of perfectly conformal thin oxide films by ALD. In this work polystyrene-b-poly(methylmethacrylate) (PS-b-PMMA) BC and reactive ion etching are used to fabricate hexagonally packed 23 nm wide nanopores in a 50 nm thick SiO2 matrix. By ALD deposition of Al2O3 thin films onto the nanoporous SiO2 templates, nanostructured Al2O3 surfaces are obtained. By properly adjusting the thickness of the Al2O3 film the dimension of the pores in the oxide films is progressively reduced, with nanometer precision, from the original size down to complete filling of the pores, thus providing a simple and fast strategy for the fabrication of nanoporous Al2O3 surfaces with well-controllable feature size.     

Molecular discrimination inside polymer nanotubules

Recognition of small organic molecules and large biomolecules such as proteins is of great importance in pharmaceutical as well as biological applications. Recognition inside a nanoporous membrane is particularly attractive, because of the advantages associated with ligand-receptor interactions in confined spaces. Classical nanoporous membrane-based separations simply use the difference in size of the analytes relative to pore size in the membrane. In order to bring about selectivity beyond size, it is necessary that methods for functionalizing the membrane pores are readily available. Here, we describe a simple approach to functionalize the nanopores within these membranes using self-assembling and non-self-assembling polymers. We show that these modified membranes separate small molecules based on size, charge and hydrophobicity. We also demonstrate here that proteins can be differentially transported through the nanopores based on their size and/or electrostatics.     

In2O3纳米孔材料的制备及其甲醛气敏性能研究

以In(NO3)3·4.5H2O为主要原料,采用溶剂热法成功地制备出In2O3纳米孔材料.采用X射线粉末衍射、透射电子显微镜等对样品的物相和形貌进行了表征和分析,并系统研究了其气敏性能.结果表明,成功合成的六方相In2O3纳米孔材料,其孔径小于17nm,孔道形状复杂且相互连通,以该材料制成的气敏元件对甲醛有很好的气敏性能,对50×10-6甲醛的灵敏度高达23.6.     

同步辐射小角X射线散射研究PAN原丝制备过程中孔结构的演变

采用同步辐射小角X射线散射研究了PAN原丝制备过程中纤维孔结构的演变。结果表明,在水洗工艺中,纤维孔隙较多、较大,孔径分布较宽,近似圆形;在热水牵伸工艺中,纤维孔隙仍较多、较大,孔径分布较宽,近似椭圆形,长轴约17 nm~21 nm,短轴约4 nm~11 nm;在干燥致密化工艺中,孔隙急剧减少、减小,孔径分布较窄,沿纤维轴向约7 nm~9nm,垂直纤维轴向约2 nm;经过蒸汽牵伸,孔隙又增多、增大,孔径分布变宽,孔隙沿纤维轴向被牵伸得很长,近似梭形;但是随后的松弛热定型又使孔隙减小,孔径分布变窄。     

Ordered nanoporous polymer-carbon composites

Nanostructured organic materials, particularly those constructed with uniform nanopores, have been sought for a long time in materials science. There have been many successful reports on the synthesis of nanostructured organic materials using the so-called, 'supramolecular liquid crystal templating' route. Ordered nanoporous polymeric materials can also be synthesized through a polymerization route using colloidal or mesoporous silica templates. The organic pore structures constructed by these approaches, however, are lower in mechanical strength and resistance to chemical treatments than nanoporous inorganic, silica and carbon materials. Moreover, the synthesis of the organic materials is yet of limited success in the variation of pore sizes and structures, whereas a rich variety of hexagonal and cubic structures is available with tunable pore diameters in the case of the inorganic materials. Here we describe a synthesis strategy towards ordered nanoporous organic polymers, using mesoporous carbon as the retaining framework. The polymer-carbon composite nanoporous materials exhibit the same chemical properties of the organic polymers, whereas the stability of the pores against mechanical compression, thermal and chemical treatments is greatly enhanced. The synthesis strategy can be extended to various compositions of hydrophilic and hydrophobic organic polymers, with various pore diameters, connectivity and shapes. The resultant materials exhibiting surface properties of the polymers, as well as the electric conductivity of the carbon framework, could provide new possibilities for advanced applications. Furthermore, the synthesis strategy can be extended to other inorganic supports such as mesoporous silicas.     

纳米多孔硅膜在医学上的应用

采用纳米技术和生物微电子机械系统技术制备纳米多孔硅膜,可准确控制膜的厚度、几何形状、孔大小、孔分布和孔隙率。纳米多孔硅膜具有优异的耐热性和化学稳定性,且可回收利用。在医学上的纳米多孔硅膜可作为药物载体、免疫隔离生物胶囊、纳米硅微镜和纳米多孔硅生物传感器。     

Inverse Opal Scaffolds and Their Biomedical Applications

Three‐dimensional porous scaffolds play a pivotal role in tissue engineering and regenerative medicine by functioning as biomimetic substrates to manipulate cellular behaviors. While many techniques have been developed to fabricate porous scaffolds, most of them rely on stochastic processes that typically result in scaffolds with pores uncontrolled in terms of size, structure, and interconnectivity, greatly limiting their use in tissue regeneration. Inverse opal scaffolds, in contrast, possess uniform pores inheriting from the template comprised of a closely packed lattice of monodispersed microspheres. The key parameters of such scaffolds, including architecture, pore structure, porosity, and interconnectivity, can all be made uniform across the same sample and among different samples. In conjunction with a tight control over pore sizes, inverse opal scaffolds have found widespread use in biomedical applications. In this review, we provide a detailed discussion on this new class of advanced materials. After a brief introduction to their history and fabrication, we highlight the unique advantages of inverse opal scaffolds over their non‐uniform counterparts. We then showcase their broad applications in tissue engineering and regenerative medicine, followed by a summary and perspective on future directions.     

Novel preparation of graded porous structures for medical engineering

The gradation of porosity in a biomaterial can be very useful for a variety of medical engineering applications such as filtration, bone replacement and implant development. However, the preparation of such structures is not a technologically trivial task and replication methods do not offer an easy solution. In this work, we elucidate the preparation of structures having a graded porosity by electrohydrodynamic spraying, using zirconia (ZrO₂), which is widely used in biomedical and other applications. The processes are generic and can be achieved using other bioactive ceramics with similar particle characteristics. The pores on the sprayed surface, the innermost surface and lengthwise cross sections have been analysed in addition to the change in depth of penetration as a function of spraying time. Control of porosity, pore size and depth of penetration has been obtained by varying parameters such as the spraying time, sintering temperature and the sacrificial template. It has been possible to obtain structures with interconnected pore networks of pore size greater than 100 μm as well as scattered pores smaller than 10 μm in size.     

Progress in the Physisorption Characterization of Nanoporous Gas Storage Materials

Assessing the adsorption properties of nanoporous materials and determining their structural characterization is critical for progressing the use of such materials for many applications, including gas storage. Gas adsorption can be used for this characterization because it assesses a broad range of pore sizes, from micropore to mesopore. In the past 20 years, key developments have been achieved both in the knowledge of the adsorption and phase behavior of fluids in ordered nanoporous materials and in the creation and advancement of state-of-the-art approaches based on statistical mechanics, such as molecular simulation and density functional theory. Together with high-resolution experimental procedures for the adsorption of subcritical and supercritical fluids, this has led to significant advances in physical adsorption textural characterization. In this short, selective review paper, we discuss a few important and central features of the underlying adsorption mechanisms of fluids in a variety of nanoporous materials with well-defined pore structure. The significance of these features for advancing physical adsorption characterization and gas storage applications is also discussed.     

A New Approach for Manufacturing a High Porosity Ti-6Al-4V Scaffolds for Biomedical Applications

Titanium and its alloys are currently considered as one of the most important metallic materials used in the biomedical applications, due to their excellent mechanical properties and superior biocompatibility. In the present study, a new effective method for fabricating high porosity titanium alloy scaffolds was developed. Porous Ti-6Al-4V scaffolds are successfully fabricated with porosities ranging from 30% to 70% using spaceholder and powder sintering technique. Based on its acceptable properties, spherical carbamide particles with different diameters （0.56, 0.8, and 1mm） were used as the space-holder material in the present investigation. The Ti-6Al-4V scaffolds porosity is characterized by using scanning electron microscopy. The results show that the scaffolds spherical-shaped pores are depending on the shape, size and distribution of the space-holder particles. This investigation shows that the present new manufacturing technique is promising to fabricate a controlled high porosity and high purity Ti-6Al-4V scaffolds for hard tissue replacement.     

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。     

Shape Memory Materials for Biomedical Applications

Shape memory properties provide a very attractive insight into materials science, opening unexplored horizons and giving access to unconventional functions in every material class (metals, polymers, and ceramics). In this regard, the biomedical field, forever in search of materials that display unconventional properties able to satisfy the severe specifications required by their implantation, is now showing great interest in shape memory materials, whose mechanical properties make them extremely attractive for many biomedical applications. However, their biocompatibility, particularly for long‐term and permanent applications, has not yet been fully established and is therefore the object of controversy. On the other hand, shape memory polymers (SMPs) show promise, although thus far, their biomedical applications have been limited to the exploration. This paper will first review the most common biomedical applications of shape memory alloys and SMPs and address their critical biocompatibility concerns. Finally, some engineering implications of their use as biomaterials will be examined.     

Change of internal/pore structure in alumina green body during initial sintering

A novel characterization method was applied to study the morphological changes of large pores in a ceramic green body during the early stage of densification at 1100°C for 1–64 h. Large processing pores were present in the green body. They were preserved after densification up to a relative density of 83.9% with their shape and size unchanged significantly. The pore size distribution determined by mercury porosimetry showed the growth of matrix pores of small size, but failed to show the change of large processing pores with densification.     

Modeling of reflected and scattered light intensity of ordered mesoporous layers of silica

Mesoporous materials are characterized by the density of empty or filled pores which modulates their properties, in particular, optical properties. Although pores scatter light, the scattered energy or reflectance spectra of a mesoporous layer show a behaviour that can be attributed mainly to interference created by the interfaces; however, coherent scattering is still present inside the mesoporous layer. In this paper, we show that diffusively reflected light created by the pores depends on their distribution and shape. If they are distributed along a periodic lattice, the structure factor modulates the optical properties and the form factor that describes the geometry of the pores, influences the shape of optical spectrum. We study the influence of the form factor of pores which renders possible a tuning of the optical reflectance spectrum through pore geometry.     

Herstellung von hochporösen,endkonturnahen Titan‐Formkörpern für biomedizinische Anwendungen

Near‐net‐shape manufacturing of highly porous titanium parts for biomedical applications The production of highly porous titanium parts is attractive for biomedical applications. Preferrentially, these parts are produced by powdermetallurgical means using suitable spacer materials. Porosities up to 75 % and well defined pore sizes in the range of 0.1 to 2.0 mm are achieved adjusting the amount and the particle size of the spacer material. Up to now, near‐net‐shape manufacturing of highly porous parts was hindered by the plastic deformation of the sintered network during machining leading to a partial or complete closing of the open porosity. A new manufacturing route is presented, where the shaping is already done in the unsintered state starting from pressed compacts. The stability of the compacts was found to be sufficient to machine the compacts without additional binders. The manufacturing route was successfully applied to the prototype of an acetabular cup. Additionally, some investigations are presented characterizing the highly porous titanium.