The chemistry of the sulfur-gold interface: in search of a unified model

Over the last three decades, self-assembled molecular films on solid surfaces have attracted widespread interest as an intellectual and technological challenge to chemists, physicists, materials scientists, and biologists. A variety of technological applications of nanotechnology rely on the possibility of controlling topological, chemical, and functional features at the molecular level. Self-assembled monolayers (SAMs) composed of chemisorbed species represent fundamental building blocks for creating complex structures by a bottom-up approach. These materials take advantage of the flexibility of organic and supramolecular chemistry to generate synthetic surfaces with well-defined chemical and physical properties. These films already serve as structural or functional parts of sensors, biosensors, drug-delivery systems, molecular electronic devices, protecting capping for nanostructures, and coatings for corrosion protection and tribological applications. Thiol SAMs on gold are the most popular molecular films because the resulting oxide-free, clean, flat surfaces can be easily modified both in the gas phase and in liquid media under ambient conditions. In particular, researchers have extensively studied SAMs on Au(111) because they serve as model systems to understand the basic aspects of the self-assembly of organic molecules on well-defined metal surfaces. Also, great interest has arisen in the surface structure of thiol-capped gold nanoparticles (AuNPs) because of simple synthesis methods that produce highly monodisperse particles with controllable size and a high surface/volume ratio. These features make AuNPs very attractive for technological applications in fields ranging from medicine to heterogeneous catalysis. In many applications, the structure and chemistry of the sulfur-gold interface become crucial since they control the system properties. Therefore, many researchers have focused on understanding of the nature of this interface on both planar and nanoparticle thiol-covered surfaces. However, despite the considerable theoretical and experimental efforts made using various sophisticated techniques, the structure and chemical composition of the sulfur-gold interface at the atomic level remains elusive. In particular, the search for a unified model of the chemistry of the S-Au interface illustrates the difficulty of determining the surface chemistry at the nanoscale. This Account provides a state-of-the-art analysis of this problem and raises some questions that deserve further investigation.     

Urban movements in Poland – a short presentation

Urban movements, borne out of civic activism in the first decade of the twenty-first century, function beyond the frameworks of official Polish urban development institutions and policies.

In the recent years they have managed to enter the political debate, some of them morphing into a clearly political form of activism, often in reaction to controversial decisions taken by local governments. Becoming increasingly aware of the number and diversity of existing organisations active in the field, they decided to form a communication and exchange platform under the name of Congress of Urban Movements. There have been already four editions of this event and as a movement they have still to clarify what directions they want to develop and what organisational form to build in order to bridge city residents’ needs with current development policies in Polish cities. They elaborated a set of 15 Urban Theses that define the basic themes that characterise their activities. However, the question remains concerning the future direction of these movements and what role will they play in the urban policies of the coming decades.     

Simple methods to fabricate Bioglass<Superscript>®</Superscript>-derived glass–ceramic scaffolds exhibiting porosity gradient

The present paper discusses different processing technologies for fabrication of novel 45S5 Bioglass^®-derived glass–ceramic scaffolds with tailored porosity gradient for potential application in bone tissue engineering. Different types of scaffolds with continuous or stepwise gradient of porosity were produced by the foam replication technique, using preformed polyurethane (PU) foams as sacrificial templates. After preforming the PU foams in metallic moulds, they were dipped in a 45S5 Bioglass^®-based slurry and subsequently heat treated in a chamber furnace up to 1100 °C. During heating, the organic phase is burned out and the glass sinters and partially crystallises. By using this new approach, Bioglass^®-derived glass-ceramic scaffolds with different shapes and porosity profiles were designed. Scanning electron microscopy (SEM) showed that all samples have highly interconnected porous structure, with specific porosity gradients. By modifying the shape and dimensions of the metallic mould, bioactive glass–ceramic scaffolds with complex shapes and different degrees of porosity gradient could be obtained.     

Polymer-bioceramic composites for tissue engineering scaffolds

Designing tissue engineering scaffolds with the required mechanical properties and favourable microstructure to promote cell attachment, growth and new tissue formation is one of the key challenges facing the tissue engineering field. An important class of scaffolds for bone tissue engineering is based on bioceramics and bioactive glasses, including: hydroxyapatite, bioactive glass (e.g. Bioglass^®), alumina, TiO₂ and calcium phosphates. The primary disadvantage of these materials is their low resistance to fracture under loads and their high brittleness. These drawbacks are exacerbated by the fact that optimal scaffolds must be highly porous (>90% porosity). Several approaches are being explored to enhance the structural integrity, fracture strength and toughness of bioceramic scaffolds. This paper reviews recent proposed approaches based on developing bioactive composites by introducing polymer coatings or by forming interpenetrating polymer-bioceramic microstructures which mimic the composite structure of bone. Several systems are analysed and scaffold fabrication processes, microstructure development and mechanical properties are discussed. The analysis of the literature suggests that the scaffolds reviewed here might represent the optimal solution and be the scaffolds of choice for bone regeneration strategies.     

Local Energy Approach to Steel Fatigue

Abstract:  This paper presents an experimental protocol developed to locally estimate different terms of the energy balance associated with the fatigue of DP600 steel. The method involves two quantitative imaging techniques. First, digital image correlation provides displacement fields and, after derivation, strain and strain-rate fields. A variational method, associated with an energy functional, is used to simultaneously identify elastic parameter and stress fields. The deformation energy rate distribution can then be determined on the basis of the stress and strain data. Secondly, infrared thermography provides thermal images which are used to separately estimate the thermoelastic source amplitude and mean dissipation per cycle distributions. The image processing uses a local form of the heat diffusion equation and a special set of approximation functions that take the frequency spectra of the sought sources into account.     

Effects of oxidation on surface stresses and mechanical properties of liquid phase pressureless-sintered SiC–AlN–Y2O3 ceramics

The understanding of the oxidation mechanism of 50 wt% SiC–50 wt% AlN composites obtained by means of pressureless sintering without the protective powder bed and with Y₂O₃ as sintering-aid were significantly improved by means of Raman spectroscopy. These analyses put in evidence that “amorphous carbon” started to be formed at 1300 °C as main effect of active oxidation of SiC. At higher temperature the crystallization process began and it was completed at 1500 °C when only graphite could be recognized. On the basis of these new evidences, oxidation effects on the mechanical properties of SiC–AlN–Y₂O₃ composites were defined. First of all, heat treatment in air was able to induce a compressive surface stress due to the volume gain associated to the oxidation of the intergranular phase. As a consequence apparent fracture toughness showed a value of 6.6 MPa m^1/2 after a heat treatment at 1300 °C, while at higher temperature effects of active oxidation caused a decreasing up to 4.7 MPa m^1/2. This toughening mechanism was also used to improve the resistance to thermal shock, which was evaluated by performing quenching tests. Furthermore, passive oxidation induced the healing of superficial flaws by means of the formation of -cristobalite. This phenomenon was assumed to be responsible for the increasing of the flexural strength.     

Signatures of clustering in superparamagnetic colloidal nanocomposites of an inorganic and hybrid nature

The individual and co-operative properties of inorganic and hybrid superparamagnetic colloidal nanocomposites that satisfy all the requirements of magnetic carriers in the biosciences and/or catalysis fields are been studied. Essential to the success of this study is the selection of suitable synthetic routes (aerosol and nanocasting) that allow the preparation of materials with different matrix characteristics (carbon, silica, and polymers with controlled porosity). These materials present magnetic properties that depend on the average particle size and the degree of polydispersity. Finally, the analysis of the co-operative behavior of samples allows for the detection of signatures of clustering, which are closely related to the textural characteristics of samples and the methodology used to produce the magnetic carriers.     

UV‐Cured Interpenetrating Acrylic‐Epoxy Polymer Networks: Preparation and Characterization

Acrylic‐epoxy interpenetrating polymer networks were prepared by means of UV curing. The photopolymerization process was investigated via real‐time FTIR spectroscopy. The hybrid, cured films showed a broad tan δ peak in DMTA demonstrating the high damping properties of the hybrid, cured formulations. A decrease on shrinkage was achieved by increasing the epoxy‐resin content in the photocurable formulation, with a consequent increase in adhesion properties.

     

Amine-based nanofibrillated cellulose as adsorbent for CO₂ capture from air

A novel amine-based adsorbent for CO? capture from air was developed, which uses biogenic raw materials and an environmentally benign synthesis route without organic solvents. The adsorbent was synthesized through freeze-drying an aqueous suspension of nanofibrillated cellulose (NFC) and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (AEAPDMS). At a CO? concentration of 506 ppm in air and a relative humidity of 40% at 25 °C, 1.39 mmol CO?/g was absorbed after 12 h. Stability was examined for over 20 consecutive 2-h-adsorption/1-h-desorption cycles, yielding a cyclic capacity of 0.695 mmol CO?/g.     

Polychlorinated biphenyls in nonaccumulating, century-old sediments: sources, signatures, and mechanism of introduction

This study documents the occurrence of highly chlorinated PCB congeners in stream sediment deposited over 100 years ago. Penta- to heptachlorinated congeners (> 80%) have been found at concentrations up to 78.8 ng/g (dw) in core samples of a small, rural tributary of Lake Ontario. Lower chlorinated congeners and other organochlorine compounds occur sporadically; 210Pb and 137Cs are lacking. The most plausible mechanism is accumulation of dissolved-phase PCBs in permeable sediments adjacent to the creek channel. The similarity between core and air samples collected in the drainage basin suggests derivation from a residual fraction of atmospherically derived PCB congeners.