Search

Abstract This paper presents Atomic Force Microscopy (AFM) as a powerful alternative to the more commonly used tensile tests for the analysis of the mechanical properties of polymeric membranes. The Young's modulus measurements by the traditional tensile tests were compared with AFM operated in Force Spectroscopy mode. AFM measurements were carried out with nanometric and micrometric tips on dense membranes of neat Pebax®1657 and on mixed matrix membranes of Pebax®1657 with different concentrations of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF 4 ]. The use of a nanometric AFM tip enables the determination of the local Young's modulus of the individual domains of the microphase-separated block-copolymer, while a larger tip gives average values of the bulk polymer. We found excellent correlation between the data obtained with common tensile tests and those obtained in compression by AFM with the micrometric tip, with important additional information on morphological features, when using the nanometric tip. This offers good perspectives for the analysis of samples where traditional tensile tests cannot be used, for instance composite membranes or particularly small samples. Graphical abstract Image Highlights • Self-standing [BMIM][BF 4 ]/Pebax®1657 membranes were successfully prepared. • AFM force spectroscopy determines mechanical properties of membranes. • Good quantitative agreement between tensile tests and force spectroscopy. • Nano-scale and bulk properties can be analysed, depending on the tip size. • A silicon environment reduces capillary forces and improves data quality. [ABSTRACT FROM AUTHOR]

Abstract: We showed the capabilities and accuracy of atomic force microscopy (AFM) techniques for imaging and analyzing the corneal epithelium and the photoablated corneal stroma. Eight normal porcine corneas, half of which were ablated using a scanning-spot excimer laser, were examined. All the corneas were imaged in balanced salt solution after fixation in glutaraldehyde. In the normal untreated corneas we observed the epithelial surface showing the typical polygonal cells and presenting numerous microprojections. The superficial epithelial cells were classified in three types as a result of the anterior-surface roughness measurements. AFM images of the photoablated corneal specimens showed undulations and granule-like features on the ablated stromal surface, specific to 193-nm ArF laser irradiation. Nevertheless, the quantitative analysis confirmed the precision of excimer laser surgery in removing sub-micrometric amounts of tissue. AFM showed to be a high-resolved imaging tool for the scanning of both native as well as photoablated corneal specimens. Also, this technique permits precise topographic analysis of the corneal plane, in the nanometric scale, of which smoothness is an important physical characteristic and necessary to achieve an optimal optical quality of the eye. [Copyright &y& Elsevier]

Highlights • The structural effects of additives for bitumen. • Wide Angle X ray Scattering (WAXS) explores the influence of additives on the bitumen structure. • Apolar Additive are preferentially located in the maltene phase weakening asphaltene inter-clusters interactions. Abstract Bitumens are composite materials whose complex organization hinders the rational understanding of their relationships between composition, structure and performances. So, research attempting to shed more light in this field is required. In this work Wide Angle X ray Scattering (WAXS) has been used to explore the influence of six opportunely chosen additives on the bitumen structure with the aim to ultimately correlate the findings with the bitumen performances. Diagnostic fingerprints have been observed in the WAXS profile: asphaltenes form stuck of about 18 Å and constituted by about 6 asphaltene units on average. Such stucks are, in turn, organized at higher levels of complexity forming anisotropic aggregates of about 200 Å × 28 Å which, again, are assembled to form micrometer-size elongated aggregates characterized by the so-called bee-structure. The structural effects of the six opportunely chosen additives (Organosilane, Polyphosphoric, Phospholipids, Acetamidophenol, Oleic Acid, octadecylamine) have been pointed out and, corroborated by AFM images, have been correlated with the rheological behavior and justified at the microscopic level: additive with an apolar nature are preferentially located in the maltene phase weakening asphaltene inter-clusters interactions and softening the bitumen, whereas, on the contrary more polar additives act in opposite directions. Peculiar behavior have been unveiled in the case of amphiphilic additive due to the simultaneous presence, within their molecular architecture, of both polar and apolar moieties. The knowledge of the detailed effect of appropriately chosen additives on the nanoscopic and mesoscopic structure and their correlation with the rheological properties constitute the first step for opening the door to the piloted design of new bitumens with desired properties for ad-hoc uses. [ABSTRACT FROM AUTHOR]

Amongst emerging Transition Metal Dichalcogenides (TMDCs), molybdenum disulfide (MoS 2) has attracted a remarkable interest thanks to many possible applications. In particular, MoS 2 has potentialities not yet fully realized in solution-based applications. However, the lack of knowledge of the optical properties of MoS 2 has significantly limited its use in many exciting photonic fields. Films prepared by solution-based exfoliation methods have never been studied to our best knowledge. The optical properties of MoS 2 films prepared by solution-based exfoliation methods have never been studied to our best knowledge. Herein, the broadband optical properties of ~20 nm-thick MoS 2 films deposited by spin-coating onto Si/SiO 2 substrates were studied by means of micro-Raman spectroscopy and Variable Angle Spectroscopic Ellipsometry (VASE). •Micro-Raman measurements of spin-coated MoS 2 films. •Micro-Raman measurements reveal the possible coexistence of 2H/1T MoS 2 phases. •VASE measurements of spin-coated MoS 2 films in a broadband photon energy range. •Dielectric response of MoS 2 films described using seven Lorentz oscillators. [ABSTRACT FROM AUTHOR]

In the last years the potential of combining the attractive materials characteristics of graphene related materials and silver nanostructures for SERS and metamaterials has emerged. Here, we report of graphene oxide thin films deposited by dip-coating on magnetron sputtered silver thin films. Our work represents a novelty in the field of the study of graphene oxide- silver composites, since magnetron sputtering deposition is an alternative way to silver thin films fabrication; previous works used instead silver nitrate aqueous solution mixed with the graphene oxide. Micro-Raman technique, morphological analysis and variable angle spectroscopic ellipsometry were performed. The final SERS signal intensity was investigated and we found Raman peaks dependent on the intensity of the laser and the thickness of silver and GO films. These results could open somestudies on plasmonics and on the reduction of graphene oxide mediated by silver thin films. Moreover, effective medium theory calculations show the possible use of these graphene oxide/silver thin films in multilayer hyperbolic metamaterials for optical applications. [ABSTRACT FROM AUTHOR]

Several phenolic compounds bind to proteins and show the ability to interfere with their aggregation process. The impact of the natural polyphenol resveratrol on the stability and heat induced aggregation of human serum albumin (HSA) was investigated by differential scanning calorimetry (DSC), attenuated total reflectance Fourier transform infrared (ATR-FTIR), UV–vis absorbance, ThT fluorescence, atomic force microscopy (AFM) and molecular modeling. The binding of resveratrol to HSA improves the stability of the protein to thermal unfolding, particularly for the energetic domain containing the ligand binding site, as modeled by computational techniques. The thermal unfolding is irreversible and after the melting the protein aggregates, either with or without the ligand. The kinetics of HSA aggregation between 70 and 80 °C shows an exponential growth of the absorbance change and it slows down when resveratrol is added. The aggregates have fibril-like morphology and resveratrol attenuates the formation of β-structured species. The overall results suggest that resveratrol stabilizes the protein structure and modulates the formation of fibrils along the initial stage of the HSA aggregation pathway. [ABSTRACT FROM AUTHOR]

This manuscript describes the gas separation performance of PIM-2, a partially fluorinated linear copolymer synthesized from 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethylspirobisindane (TTSBI) and decafluorobiphenyl (DFBP). As one of the early members of the family of polymers of intrinsic microporosity, it had never been tested as a gas separation membrane because of insufficient mechanical resistance. This has been solved only recently, allowing the preparation of robust self-standing films. Molecular modelling studies demonstrated a high fractional free volume (34%) and an elevated surface area (642 m2 g−1), and the latter is in good agreement with experimental BET results. Pure gas permeabilities measured on a fixed-volume time-lag instrument at 1 bar compare well with the results of mixed separation tests on a variable volume setup from 1-6 bar(a). Molecular modelling and independent sorption measurements on a gravimetric sorption balance both show strong dual-mode sorption behaviour, especially for CO 2 and to a lesser extent for CH 4. Temperature-dependent pure gas permeation measurements show typical Arrhenius behaviour, with a clear increase in the activation energy for diffusion with the increasing molecular size of the gas, indicating high size-selectivity. This is in agreement with the highly rigid PIM structure, determined by AFM force spectroscopy measurements. The dual-mode behaviour results in a moderate pressure dependence of the CO 2 permeability and the CO 2 /N 2 and CO 2 /CH 4 selectivity, all slightly decreasing with increasing pressure. The presence of humidity in the gas stream has a remarkable small effect on the membrane performance, which is probably due to the high fluorine content and the consequently low water vapour solubility in the polymer, as confirmed by gravimetric sorption measurements. The manuscript describes an extensive study on the structure-property relationships in PIM-2. Image 1 • Fluorinated PIM-2 forms robust self-standing membranes. • CO 2 /N 2 and CO 2 /CH 4 mixed gas separation data lie close to the 2008 upper bound. • Separation performance is hardly affected by the presence of humidity in the feed gas. • Water sorption is very low due to the hydrophobic nature of the fluoropolymer. • MD simulations show how halogen bond networks enhance the energetic diffusion selectivity. [ABSTRACT FROM AUTHOR]