New selective dissolution process to quantify reaction extent and product stability in metakaolin-based geopolymers

A selective dissolution process is developed that can quantify the amount of soluble material, geopolymer gel and remnant unreacted precursor in metakaolin-based geopolymer systems and determine the nanostructural features of the raw materials and geopolymer gel components. The susceptibility of alkalis leachability from the alkaline aluminosilicate hydrate-type gel (N-A-S-H) produced during the geopolymerization is not fully understood. This phenomenon led to deleterious processes from a microstructural, aesthetic and performance point of view. Geopolymers were synthesised using different contents and types of alkalis (M/Al = 0.50–0.83, where M represents Na or K), different contents of soluble silica in the activator (expressed as SiO2/M2O ratio of 1.0, 0.5 and 0.0), and curing temperatures (25 and 50 °C). The selective dissolution process is based on neutral dissolution at pH 7 to extract the soluble materials and acid dissolution using a strong acid at pH 0 to dissolve the geopolymer gel, which provides for the first time a method to quantify the (i) soluble material, (ii) geopolymer gel and (iii) unreacted material in geopolymers. The soluble material provides a reliable indication of the materials that can be removed from the geopolymers in a neutral pH environment and hence the potential for leaching and efflorescence, which is useful for durability prediction and service life. Quantification of remnant unreacted metakaolin determines the reactivity of the precursor and assesses the suitability of different synthesis conditions for varied applications. This work therefore provides a novel and widely applicable approach to determine the susceptibility of geopolymer materials to leaching

Durable Modified Polyacrylic Coatings for Cultural Heritage Protection

INTRODUCTION Deterioration phenomena of ancient and modern stone cultural heritage are natural and unrestrainable decay processes mainly arising from water adsorption and percolation into stone building materials1. Once water attacks and penetrates stone surfaces, several chemical, physical and biological degradation processes can occur altering significantly, and in some cases even irreversibly, the properties of stone materials. The application of hydrophobic coatings to stone surfaces is mandatory to protect stone artefacts from the deleterious effects occurring in the case of water exposition. The protective agent must possess several features, i.e. high compatibility with the substrate, high durability, transparency, easiness of application and removal, water-repellency, capability to avoid the attack of organic and inorganic contaminants; moreover, it should be permeable to water vapor. The aim of the present work was to synthesize new polymer coatings as stone protective with satisfactory water repellent properties and improved durability, thanks to the combined use of fluorinated and long alkyl chain monomers and without the use of any photo stabilizers agents. EXPERIMENTAL/THEORETICAL STUDY New types of polymer protectives were prepared via free radical polymerization between either 1H,1H,2H,2H-Perfluoro-octyl-methacrylate (POMA) or commercial stearyl methacrylate (STEA, Sigma Aldrich) and methacrylic monomers (methyl, MMA, and n-butyl, nBuMA, methacrylates)2,3. Specifically, POMA was synthesized via esterification reaction using methacryloyl chloride and 1H,1H,2H,2H-Perfluoro-1-octanol. RESULTS AND DISCUSSION The properties of the home-made hydrophobizing polymers in terms of macromolecular structure, molecular weights, thermal features and water repellency were determined. Furthermore, the long-term behavior of these polymeric protective agents was estimated by means of accelerated aging tests exploiting UV radiations (in according to UNI 10925:2001 standard method for 100h, 315-400 nm for UVA rays and 280-315 nm for UVB ones). Their behavior over time was checked via Size Exclusion Chromatography (SEC) by evaluating Mn and D data of aged polymeric samples (Table 1) and by Fourier Transform Infrared (FT-IR) spectroscopy. By evaluating Mn and D data reported in Table 1, all the synthesized polymers seem to be unaffected by UV aging. Thus, the present stable resins were applied on both natural (Botticino marble) and artificial (mortar) stone substrates and their wetting properties together with their absorption by capillarity and water vapour permeability were successfully assessed and compared. All the covered substrates show an increase of water contact angle of around 50\ub0 and a decrease in water absorption and permeation of about 50% and 20%, respectively. Lastly, in order to evaluate the stability of the applied coatings towards degradation induced by solar radiation and interaction with the atmospheric pollution, exposure to a typical polluted urban environment for some months have been carried out. For this purpose, the following analyses have been performed: contact angle measurements, SEM-EDS (Scanning Electron Microscopy with X-ray microanalysis), IC (Ion Chromatography), and colorimetric tests by CIELab elaboration. CONCLUSION The use of polymeric protectives is very advantageous in fields when the hydrophobic properties and high chemical stability are required. Within this context, the use of polymer resins bearing methacrylic and fluorinated monomers along the polymeric chain can be a way to create tailor-made water repellent materials with enhanced durability, without the addition of any stabilizing agent

Metakaolin-based geopolymers: Relation between formulation, physicochemical properties and efflorescence formation

The efflorescence formation in metakaolin-based geopolymers is assessed in this study to provide a better understanding of the effect of the synthesis parameters. Efflorescence formation depends on the physical and chemical properties of geopolymers as well as the environmental exposure conditions. In this study a set of fifteen geopolymers were synthesized using different formulation. An accelerated test of efflorescence development is presented, where the grade of degradation was evaluated by visual observation and correlated to leaching potential, physical properties and microstructural features. The use of soluble silicate in the activator provides a denser and a less permeable matrix. This makes the extraction of free alkalis to the surface more difficult, reducing the extent of alkali leaching and therefore efflorescence. The use of K+ is also effective to reduce visible efflorescence. The efflorescence formation is predicted by the properties of the gel formed which are dependent on the mix proportioning

Resonant laser tunnelling

We propose an experiment involving a gaussian laser tunneling through a twin barrier dielectric structure. Of particular interest are the conditions upon the incident angle for resonance to occur. We provide some numerical calculations for a particular choice of laser wave length and dielectric refractive index which confirm our expectations.Comment: 15 pages, 6 figure

Dispersive properties of quasi-phase-matched optical parametric amplifiers

The dispersive properties of non-degenerate optical parametric amplification in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary grating profile are theoretically investigated in the no-pump-depletion limit. The spectral group delay curve of the amplifier is shown to be univocally determined by its spectral power gain curve through a Hilbert transform. Such a constraint has important implications on the propagation of spectrally-narrow optical pulses through the amplifier. In particular, it is shown that anomalous transit times, corresponding to superluminal or even negative group velocities, are possible near local minima of the spectral gain curve. A possible experimental observation of such effects using a QPM Lithium-Niobate crystal is suggested.Comment: submitted for publicatio

Static Observers in Curved Spaces and Non-inertial Frames in Minkowski Spacetime

Static observers in curved spacetimes may interpret their proper acceleration as the opposite of a local gravitational field (in the Newtonian sense). Based on this interpretation and motivated by the equivalence principle, we are led to investigate congruences of timelike curves in Minkowski spacetime whose acceleration field coincides with the acceleration field of static observers of curved spaces. The congruences give rise to non-inertial frames that are examined. Specifically we find, based on the locality principle, the embedding of simultaneity hypersurfaces adapted to the non-inertial frame in an explicit form for arbitrary acceleration fields. We also determine, from the Einstein equations, a covariant field equation that regulates the behavior of the proper acceleration of static observers in curved spacetimes. It corresponds to an exact relativistic version of the Newtonian gravitational field equation. In the specific case in which the level surfaces of the norm of the acceleration field of the static observers are maximally symmetric two-dimensional spaces, the energy-momentum tensor of the source is analyzed.Comment: 28 pages, 4 figures

Comparison of Branched and Linear Perfluoropolyether Chains Functionalization on Hydrophobic, Morphological and Conductive Properties of Multi-Walled Carbon Nanotubes

The functionalization of multi-walled carbon nanotubes (MW-CNTs) was obtained by generating reactive perfluoropolyether (PFPE) radicals that can covalently bond to MW-CNTs\u2019 surface. Branched and linear PFPE peroxides with equivalent molecular weights of 1275 and 1200 amu, respectively, have been thermally decomposed for the production of PFPE radicals. The functionalization with PFPE chains has changed the wettability of MW-CNTs, which switched their behavior from hydrophilic to super-hydrophobic. The low surface energy properties of PFPEs have been transferred to MW-CNTs surface and branched units with trifluoromethyl groups, CF3, have conferred higher hydrophobicity than linear units. Porosimetry discriminated the effects of PFPE functionalization on meso-porosity and macro-porosity. It has been observed that reactive sites located in MW-CNTs mesopores have been intensively functionalized by branched PFPE peroxide due to its low average molecular weight. Conductivity measurements at different applied pressures have showed that the covalent linkage of PFPE chains, branched as well as linear, weakly modified the electrical conductivity of MW-CNTs. The decomposed portions of PFPE residues, the PFPE chains bonded on carbon nanotubes, and the PFPE fluids obtained by homo-coupling side-reactions were evaluated by mass balances. PFPE-modified MW-CNTs have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), static contact angle (SCA), surface area, and porosity measurements

Genetically modified NT2N human neuronal cells mediate long-term gene expression as CNS grafts in vivo and improve functional cognitive outcome following experimental traumatic brain injury

Human Ntera-2 (NT2) cells can be differentiated in vitro into well-characterized Populations of NT2N neurons that engraft and mature when transplanted into the adult CNS of rodents and humans. Them ha e shown promise as treatments for neurologic disease, trauma, and ischemic stroke. Although these features suggest that NT2N neurons would be an excellent platform for ex vivo gene therapy in the CNS, stable gene expression has been surprisingly difficult to achieve in these cells. In this report we demonstrate stable, efficient. and nontoxic gene transfer into undifferentiated NT2 cells using a pseudotyped lentiviral vector encoding the human elongation factor 1-alpha promoter and the reporter gene eGFP, Expression of eGFP was maintained when the NT2 cells were differentiated into NT2N neurons after treatment with retinoic acid, When transplanted into the striatum of adult nude mice, transduced NT2N neurons survived, engrafted, and continued to express the reporter gene for long-term time points in vivo. Furthermore. transplantation of NT2N neurons genetically modified to express nerve growth factor significantly attenuated cognitive dysfunction following traumatic brain injure in mice. These results demonstrate that defined populations of genetically modified human NT2N neurons are a practical and effective platform for stable ex vivo gene delivery into the CNS