Hydration process of cement in the presence of a cellulosic additive. A calorimetric investigation

In the cement industry, the extrusion technique is used to produce flat shapes with improved resistance to compression. Extrusion is a plastic-forming process that consists of forcing a highly viscous plastic mixture through a shaped die. The material should be fluid enough to be mixed and to pass through the die, and on the other hand, the extruded specimen should be stiff enough to be handled without changing in shape or cracking. These characteristics are industrially obtained by adding cellulosic polymers to the mixture. The aim of this work is to understand the action mechanism of these additives on the major pure phases constituting a typical Portland cement: tricalcium silicate (C(3)S), dicalcium silicate (C(2)S), tricalcium aluminate (C(3)A), and tetracalcium iron-aluminate (C(4)AF). In particular, a methylhydroxyethyl cellulose (MHEC) was selected from the best-performing polymers for further study. The effect of this additive on the hydration kinetics (rate constants, activation energies, and diffusional constants) was evaluated by means of differential scanning calorimetry (DSC) while the hydration products were studied by using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). MHEC addition in calcium silicate pastes produces an increase in the induction time without affecting the nucleation-and-growth period. A less dense CSH gel was deduced from the diffusional constants in the presence of MHEC. Moreover, CSH laminar features and poorly structured hydrates were noted during the first hours of hydration. In the case of the aluminous phases, the additive inhibits the growth of stable cubic hydrated phases (C(3)AH(6)), with the advantage of the metastable hexagonal phases being formed in the earliest minutes of hydration.     

The chemistry and the stereochemistry of poly(N-alkyliminoalanes) : XV. The crystal and molecular structure of the compounds [((THF)Mg)(HA1N-t-Bu)3] and [((THF)3Ca)(HA1N-t-Bu)3] · THF

The compounds [((THF)Mg)(HA1N-t-Bu)₃] (I) and [((THF)₃Ca)(HA1N-t-Bu)₃] · THF (II) have been structurally characterized from single-crystal diffraction data. The molecular structures are based on an (A1N)₄ “cubane” type framework in which an aluminum is replaced by an alkaline earth metal. According to the size and the coordination of the “foreign” atom (four for Mg, six for Ca) the cubic geometry of the cage is increasingly distorted. Coordination is completed by one molecule of THF to the Mg atom and three molecules to the Ca atom; in II a molecule of THF crystallizes with a cage molecule. Mean MgN and CaN bond distances are 2.090(4) and 2.490(2) Å. Crystal data: I, orthorombic, space group Pbca, a 17.107(2), b 17.305(4) and c 20.220(5) Å, Z = 8, calculated density 1.031 g/cm³; II, orthorombic, space group Pbca, a 20.48(1), b 20.38(1), c 20.51(1), Z = 8, calculated density 1.081 g/cm³.     

A complete family of isostructural cluster compounds with cubane-like M(3)S(4)M' cores (M = Mo,W; M' = Ni,Pd, Pt): comparative crystallography and electrochemistry

By reaction of the geometrically incomplete cubane-like clusters [(eta(5)-Cp')(3)Mo(3)S(4))][pts] and [(eta(5)-Cp')(3)W(3)S(4)][pts] (Cp' = methylcyclopentadienyl; pts = p-toluenesulfonate) with group 10 alkene complexes, three new heterobimetallic clusters with cubane-like cluster cores were isolated: [(eta(5)-Cp')(3)W(3)S(4)M'(PPh(3))][pts] ([5][pts], M' = Pd; [6][pts], M' = Pt); [(eta(5)-Cp')(3)Mo(3)S(4)Ni(AsPh(3))][pts] ([7][pts]). The compounds [5][pts]-[7][pts] are completing the extensive series of clusters [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] (M = Mo, W; M' = Ni, Pd, Pt; E = P, As) which allows the consequences of replacing a single type of atom on structural and NMR and UV/vis spectroscopic as well as electrochemical properties to be determined. Single-crystal X-ray structure determinations of [5][pts]-[7][pts] revealed that [5][pts] was not isomorphous to the other members of the series [(eta(5)-Cp')(3)M(3)S(4)M'(EPh(3))][pts] due to distinctly different cell parameters, which in the molecular structure of [5](+) is reflected in a slightly different orientation of the PPh(3) ligand. Electrochemical measurements on the series showed that the Mo-based clusters were more difficult to oxidize than their W-based analogues. The Pd-containing clusters underwent two-electron oxidation processes, whereas the Ni- and Pt-containing clusters underwent two separated one-electron oxidation processes.     

A nonlinear hyperbolic problem arising from a question of nonlinear optics, Part II

A modified analytical and numerical method is presented for a preliminary study of the problem of Graffi-Cesari in Nonlinear Optics [1, 12]. This problem concerns electromagnetic laser wave propagation in a nonlinear (quartz) crystal slab embedded between two linear media, and is a suitably simplified version of the experimental situation of Franken, Ward and co-workers (1961). A new version of an existence and uniqueness theorem is proved in a functional class which is chosen following Cesari's works on quasilinear hyperbolic systems in the Schauder canonic form, under a set of restrictions upon the admissible slab widtha of the crystal. The present method consists essentially in centering the relevant functional ball at the linear solution, and yields numerical values fora of the order of 2 mm, with a good agreement with values of quartz crystal widths used in experiments.     

A nonlinear hyperbolic problem arising from a question of nonlinear optics,part I

Summary Analytical and numerical results are given for the problem of Graffi, recently proposed by D. Graffi in order to give a rigorous mathematical theory of the experiments carried out by Franken, Ward and coworkers (1961) in Nonlinear Optics, following the theoretical scheme developed by L. Cesari in some recent papers concerning boundary value problems for quasilinear hyperbolic systems in the Schauder canonic forms.Numerical results refer to the estimate by defect of the maximal slab widtha of the nonlinear medium (a quartz crystal slab), under which the relevant existence and uniqueness theorem holds, in a suitable functional class which is chosen following Cesari's works and is well-suited for applications to Mathematical Physics.

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Riassunto Si presentano risultati analitici e numerici relativi al problema di Graffi, recentemente proposto da D. Graffi per una teoria matematica degli esperimenti di Franken, Ward et al. (1961) in Ottica Non Lineare, seguendo lo schema teorico elaborato da L. Cesari in alcuni recentissimi lavori su certi problemi ai limiti per sistemi iperbolici quasi lineari nella forma canonica di Schauder.I risultati numerici si riferiscono alla stima per difetto del massimo spessore del mezzo non lineare (lamina di cristallo di quarzo) per cui restano validi teoremi di esistenza, unicità e dipendenza continua dall'onda (laser) incidente, in una opportuna classe funzionale, scelta seguendo i lavori citati di Cesari.

     

Magneto-responsive nanocomposites: Preparation and integration of magnetic nanoparticles into films,capsules, and gels

This review reports on the latest developments in the field of magnetic nanocomposites, with a special focus on the potentials introduced by the incorporation of magnetic nanoparticles into polymer and supramolecular matrices. The general notions and the state of the art of nanocomposite materials are summarized and the results reported in the literature over the last decade on magnetically responsive films, capsules and gels are reviewed. The most promising concepts that have inspired the design of magneto-responsive nanocomposites are illustrated through remarkable examples where the integration of magnetic nanoparticles into organic architectures has successfully taken to the development of responsive multifunctional materials.     

Interaction of Naproxen with Crystalline and Amorphous Methylated β-Cyclodextrin in the Liquid and Solid State

Abstract

Interactions of naproxen (NAP) with amorphous, randomly methylated β-cyclodextrin at a degree of substitution per anhydroglucose unit of 1.8 (RAMEB) and with crystalline heptakis-(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) were studied in aqueous solution and in the solid state using, respectively, phase-solubility analysis (at 25 °C, 37 °C and 47 °C) and differential scanning calorimetry (DSC) supported by X-ray powder diffractometry. RAMEB and DIMEB displayed similar solubilizing and complexing abilities towards NAP, suggesting analogous inclusion modes of the drug in the host cavity in aqueous solution. Differences were instead observed in interactions in the solid state, where the amorphizing capacity of RAMEB toward NAP (evaluated by DSC) was about twice that of DIMEB at each drug-to-carrier ratio. Assuming that inclusion complexation is also involved in solid-state interactions, molecular modelling accounted for the experimental results in terms of structural features of DIMEB, i.e. the particular inwards orientation of O-6-C-8 groups of three alternate glucoses on the primary hydroxyl side which hampers a deep penetration of NAP in the DIMEB cavity in the solid state. On the contrary, no obstruction of the cavity apparently occurs with RAMEB due its noncrystalline state. The aqueous dissolution rate of NAP from NAP-RAMEB and NAP-DIMEB blends containing 0.59, 0.73, 0.85, and 0.92 mass fraction of carrier linearly increased at decreasing drug-to-carrier ratios. The improvement was 5 to 20 times (from powders) and 50 to 200 times (from discs) the dissolution rate of NAP alone for both carrier. Therefore the choice of the amorphous RAMEB in pharmaceutical formulations can be recommended mainly for economic reasons, though the anhydrous and non-hygroscopic nature of crystalline DIMEB might be of particular advantage in case of moisture sensitive formulations.     

Smart Coatings Prepared via MAPLE Deposition of Polymer Nanocapsules for Light-Induced Release

Herein, smart coatings based on photo-responsive polymer nanocapsules (NC) and deposited by laser evaporation are presented. These systems combine remotely controllable release and high encapsulation efficiency of nanoparticles with the easy handling and safety of macroscopic substrates. In particular, azobenzene-based NC loaded with active molecules (thyme oil and coumarin 6) were deposited through Matrix-Assisted Pulsed Laser Evaporation (MAPLE) on flat inorganic (KBr) and organic (polyethylene, PE) and 3D (acrylate-based micro-needle array) substrates. SEM analyses highlighted the versatility and performance of MAPLE in the fabrication of the designed smart coatings. DLS analyses, performed on both MAPLE- and drop casting-deposited NC, demonstrated the remarkable adhesion achieved with MAPLE. Finally, thyme oil and coumarin 6 release experiments further demonstrated that MAPLE is a promising technique for the realization of photo-responsive coatings on various substrates.     

Binding free energy predictions in host-guest systems using Autodock4. A retrospective analysis on SAMPL6, SAMPL7 and SAMPL8 challenges

Journal of Computer-Aided Molecular Design - We systematically tested the Autodock4 docking program for absolute binding free energy predictions using the host-guest systems from the recent SAMPL6,...