Nature has evolved materials that possess mechanical properties surpassing many man-made composites. Bones, teeth, spider silk, or nacre, are just a few well-known examples of biomaterials that exhibit exceptionally high tensile strengths, hardness, or toughness. [1][2][3][4][5][6] These remarkable properties have driven scientists to study and model their architectures and compositions, from micro-to nanoscales, in the hope of developing analogous synthetic materials. Of these, probably the most studied is nacre. [4,[7][8][9][10][11][12][13][14][15] It is composed of 95 % brittle CaCO 3 plates with just a few percent of organic "glue", yet it is twice as hard and more than ca. 1000 times as tough as its constituent phases. [16] These exceptional mechanical properties together with the macroscopic beauty and elegance of its nanoscale hierarchy serve as a model for design of high-performance materials. Preparation of artificial analogs of nacre has been approached by using several different methods and the resulting materials capture some of the characteristics of the natural composite. [17][18][19][20][21][22][23] In our own work, we have used a layerby-layer (LBL) assembly technique to prepare a nanostructured analogue of nacre from inorganic nanometer-sized sheets of Na + -Montmorillonite clay (C) and a polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA).[24] The structure, deformation mechanism, and mechanical properties of this material were found to be comparable with those of natural nacre and lamellar bones (tensile strength, r = (100 ± 10) MPa, and Young's modulus, Y = (11 ± 2) GPa). Contrary to other preparation techniques the LBL method is relatively simple and highly versatile in merging different functionalities into a single composite. [25][26][27] At the same time, a vast array of available assembly components allows us to generate alternative designs as a means of understanding the different interactions necessary for preparation of nacrelike composites with application-tailored mechanical responses. LBL technique has proven to be an ideal method for preparation of multifunctional, nanostructured materials. Since its inception in 1990s, [28] there has been a virtual explosion in the amount of scientific literature in this subject. Similarly, LBL assembly of clays was also pioneered and further studied in the 1990s by Ferguson's group. [29,30] Since then, the LBL technique has been found to be applicable for the preparation of superhydrophobic surfaces, [31] sensors and semipermeable membranes, [32][33][34][35] drug and biomolecules delivery, [36,37] optically active and responsive films, [38][39][40] fuel cells and photovoltaic materials, [41,42] biomimetic and bioresponsive coatings, [43] semiconductors, [44,45] catalysts, [46] and magnetic devices, [26,47] to name a few. All of the potential applications mentioned above also require both control and improvement of mechanical properties. Using the mix-and-match approach to LBL films, that is, stratified multilayers, [25,26,44] the mecha...
The purpose of this study was to evaluate the feasibility of metabonomics technology for developing a rapid-throughput toxicity screen using 2 known hepatotoxicants: carbon tetrachloride (CCl(4)) and alpha-naphthylisothiocyanate (ANIT) and 2 known nephrotoxicants: 2-bromoethylamine (BEA) and 4-aminophenol (PAP). In addition, the diuretic furosemide (FURO) was also studied. Single doses of CCl(4) (0.1 and 0.5 ml/kg), ANIT (10 and 100 mg/kg), BEA (15 and 150 mg/kg), PAP (15 and 150 mg/kg) and FURO (1 and 5 mg) were administered as single IP or oral doses to groups of 4 male Wistar rats/dose. Twenty-four-h urine samples were collected pretest, daily through Day 4, and on Day 10 (high dose CCl(4) and BEA only). Blood samples were taken on Days 1, 2, and 4 or 1, 4, and 10 for clinical chemistry assessment, and the appropriate target organ was examined microscopically. NMR spectra of urine were acquired and the data processed and subjected to principal component analyses (PCA). The results demonstrated that the metabonomic approach could readily distinguish the onset and reversal of toxicity with good agreement between clinical chemistry and PCA data. In at least 2 instances (ANIT and BEA), PCA analysis suggested effects at low doses, which were not as evident by clinical chemistry or microscopic analysis. Furosemide, which had no effect at the doses employed, did not produce any changes in PCA patterns. These data support the contention that the metabonomic approach represents a promising new technology for the development of a rapid throughput in vivo toxicity screen.
This paper discusses the limitations of parametric modelling of corrosion and presents the case that accurate and exible models of atmospheric corrosion require an 'holistic' approach. In such an approach, the processes controlling corrosion across a wide range of physical scales are modelled. These models are based as much as possible on the processes controlling the phenomena under consideration. Being fundamentally based, these models can be extended outside the data sets from which they are derived. This is the rst of a series of papers outlining the use of this approach to predict corrosion in marine environments. It will consider the theoretical formulations required to model the production, transport and deposition of marine salts. It will present some predictions from these formulations and it will discuss the implications to corrosion of this theoretical understanding. Later papers will present the incorporation of these models into an information system and the validation of these models against data. CEST/2057 The authors are with CSIRO Manufacturing and Infrastructure Technologies,
Layer-by-layer (LBL) assembly is one of the most ubiquitous coating techniques today. It also offers a pathway for multifunctional/multicomponent materials with molecular-scale control of stratified structures. However, technological applications of LBL are impeded by laborious and fluid-demanding nature of the process. While vertical organization of LBL films is natural for this technique, the control of lateral organization of the films is fairly difficult. Using the deposition of carbon nanotubes (SWNTs) and other nanoscale colloids, we introduce here a new approach to LBL based on dewetting phenomena, d-LBL. Its strengths include: (1) elimination of rinsing steps, (2) significant acceleration of the process, (3) improvement of lateral organization of LBL films, and (4) ability to produce nanostructured coatings from colloids when classical LBL fails. The generality of d-LBL can compete with traditional LBL and is demonstrated for cellulose nanowires, polyelectrolyte pairs, and semiconductor nanoparticles, metal oxides, and Au nanorods.
This paper explores the simple principle that a metal surface wets when the surface relative humidity ͑RH͒ exceeds the deliquescent RH ͑DRH͒ of any salts on the surface. Data from field exposures across 19 sites in China, the Philippines, Indonesia, and Australia is used to determine the conditions under which openly exposed surfaces wet. At each site, surface temperature ͑of a zinc plate͒, ambient RH, sensor wetness, airborne salinity, and gaseous SO x and NO x were determined over a one-year period. In conjunction with these microclimate measures, the chemistry of airborne and deposited aerosols, as well as rainwater, were measured. Complimentary data from an environmental scanning electron microscope are presented in which salts derived from the evaporation of sea salt are rewetted. Using all of this data, an assessment of the probable contaminants controlling sensor wetting at each site is made. It is found that sites with similar International Standard Organization, ͑ISO͒ 9223, classifications in terms of industrial and marine airborne pollutants show similar surface contaminants and wetting characteristics. It is proposed that dominant contaminates can be identified for each ISO classification that are consistent with the general principle that wetting occurs when surface RH exceeds the DRH of the salts making up the contaminates. These salts can change from day to day due to the continual change in the composition of the contaminates and the ongoing homogenization of previously deposited salts through chemical reaction between salts and with the surface. Rain events usually clean the surface and start the cycle over again. The application of these findings to process models of corrosion is discussed, while generalized rules for predicting surface wetting based on climate data are proposed. It is found that these generalized rules predict total time of wetness to a high degree of accuracy.The concept of time of wetness ͑TOW͒ has been a very useful one for atmospheric corrosion scientists. 1 Indeed, the principle that corrosion can only occur in the presence of an electrolyte is based on fundamental electrochemical considerations. 2 Since the TOW concept was first proposed, sensors to measure TOW, 3-5 dose functions to define metallic corrosion 6-8 as a function of TOW, and degradation maps 9 based on these dose functions have been developed. However, the approximation commonly used to estimate TOW and included in International Standard Organization ͑ISO͒ 9225 ͓that TOW is the time when temperature is above 0°C and relative humidity ͑RH͒ is above 80%͔ cannot be directly derived from an understanding of the processes of surface wetting. Further studies of hygroscopic salts and aerosols indicate that salts, and thus the surfaces that they are on, may wet over a range of RH, depending on the deliquescent RH ͑DRH͒ of the salt. [10][11][12] In recent years, a number of authors have proposed refinements to the TOW concept in order to either derive better statistical fit with their corrosion data, or to account for...
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