Search results for "strength"
showing 10 items of 2415 documents
Speciation of chitosan with low and high molecular weight carboxylates in aqueous solution
2009
Quantitative data on the speciation of chitosan (310 kDa) with low and high molecular weight carboxylates in aqueous solution are reported. The following carboxylic ligands were considered: monocarboxylate (butyrate); dicarboxylates (malonate, succinate, azelate); tricarboxylate (1,2,3-propa- netricarboxylate); tetracarboxylate (1,2,3,4-butanetetracarboxylate); polyacrylates (2.0 and 20 kDa); polymethacrylate (5.4 kDa). The investigation was performed by potentiometry at t 1/4 25 C, at low ionic strength (without addition of supporting electrolyte) and at I 1/4 0:15 mol L 1 (NaCl). For all the systems the formation of (chitosan)LHi species was found (L 1/4 carboxylic ligand; i 1/4 1 to 4 de…
Sequestration of organomettalic compounds by synthetic and naturally occuring polycarboxylate ligands. Binding of monomethylmercury(II) by polyacryli…
2007
The sequestering capacity of synthetic and naturally occurring polycarboxylate ligands towards mono- methylmercury(II) was evaluated by stability quantitative data on the interaction of CH3Hgþ with different molecular weight synthetic polyacrylates (2 and 20 kDa average M.wt) and alginate (70– 100 kDa) extracted from brown algae Macrocystis pyrifera. The influence of ionic medium was evaluated by measurements on the CH3Hgþ-polyacrylate systems in NaNO3 medium at different ionic strengths (0.10, 0.25, 0.50 and 0.75mol Lÿ1), and a Debye–Hu¨ ckel type equation was used for the dependence of complex formation constants on ionic strength. Measurements on the CH3Hgþ - alginate system were carried…
Salt-induced microheterogeneities in binary liquid mixtures
2017
The salt-induced microheterogeneity (MH) formation in binary liquid mixtures is studied by small-angle x-ray scattering (SAXS) and liquid state theory. Previous experiments have shown that this phenomenon occurs for antagonistic salts, whose cations and anions prefer different components of the solvent mixture. However, so far the precise mechanism leading to the characteristic length scale of MHs has remained unclear. Here, it is shown that MHs can be generated by the competition of short-ranged interactions and long-ranged monopole-dipole interactions. The experimental SAXS patterns can be reproduced quantitatively by fitting to the derived correlation functions without assuming any speci…
New Lignocellulosic Aristida adscensionis Fibers as Novel Reinforcement for Composite Materials: Extraction, Characterization and Weibull Distributio…
2019
In this research, the Aristida adscensionis fibers (AAFs) were taken out from the plants and its fundamental properties anlayzed for the first time. The AAFs were characterized and compared with other natural fibers by the use of physico-chemical analysis and various characterization techniques such as FT-IR, XRD, NMR, TGA, SEM and AFM. Chemical analysis showed that A. adscensionis fibers have a high cellulose content of 70.78% whereas the contents of lignin and wax are equal to 8.91% and 2.26%, respectively. The FT-IR, XRD and NMR analysis confirmed that AAFs are rich in cellulose content with CI and CS equal to 58.9% and 11.5 nm, respectively. Pycnometer analysis allowed to estimate a den…
Giant Mechanocaloric Effects in Fluorite-Structured Superionic Materials
2016
Mechanocaloric materials experience a change in temperature when a mechanical stress is applied on them adiabatically. Thus, far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterized by …
Creep and recovery of epoxy/MWCNT nanocomposites
2012
Abstract Creep and creep–recovery of epoxy/multi-wall carbon nanotube (MWCNT) composites was studied in a wide range of applied loads in order to evaluate the contribution of nanotubes on the time-dependent behaviour of the epoxy matrix. Incorporation of up to 1 wt.% of C150P MWCNTs has negligible influence on the elastic, viscoelastic and viscoplastic response of the epoxy system. No systematic changes of the creep characteristics depending on the content of nanotubes are noticed in the range of stresses from 0.3 up to 0.75 from the ultimate strength. Creep resistance and recovery performance of the epoxy matrix is not negatively affected by the addition of MWCNTs and the same analytical m…
The Reduction Pathway of End-on Coordinated Dinitrogen. I. Vibrational Spectra of Mo/W−N2, −NNH, and −NNH2 Complexes and Quantum Chemistry Assisted N…
1999
Infrared and Raman spectra of [M(N(2))(2)(dppe)(2)] (M = W, Mo) and the two protonated derivatives [WF(NNH)(dppe)(2)] and [WF(NNH(2))(dppe)(2)](+) (dppe = 1,2-bis(diphenylphosphino)ethane) are presented. Using isotope substituted compounds ((15)N and D) the vibrations of the Y-M-N(2)H(x)() (x = 0, 1, 2; Y = N(2), F) central unit are identified, in particular the M-N and N-N stretching modes. In case of the monoprotonated systems, an equilibrium between metal- and nitrogen-protonated species exists that is clearly detectable in the IR spectra. Making use of theoretical force fields, a quantum chemistry assisted normal coordinate analysis (QCA-NCA) is performed for all three tungsten systems …
Analysis and parametric sensitivity of the behavior of overshoots in the concentration of a charged adsorbate in the adsorbed phase of charged adsorb…
2003
In this work, an analysis of the parametric sensitivity of the overshoot in the concentration of the adsorbate in the adsorbed phase, which occurs under certain conditions during an ion-exchange adsorption process, is presented and used to suggest practical implications of the concentration overshoot phenomenon on operational policies and configurations of chromatographic columns and finite bath adsorption systems. The results presented in this work demonstrate and explain how the development of an overshoot in the concentration of the adsorbate in the adsorbed phase could be enhanced or suppressed by (i) varying the diffusion coefficient, D3, of the adsorbate relative to the diffusion coef…
Studies on supramolecular gel formation using DOSY NMR
2015
Herein, we present the results obtained from our studies on supramolecular self-assembly and molecular mobility of low-molecular-weight gelators (LMWGs) in organic solvents using pulsed field gradient (PFG) diffusion ordered spectroscopy (DOSY) NMR. A series of concentration-dependent DOSY NMR experiments were performed on selected LMWGs to determine the critical gelation concentration (CGC) as well as to understand the behaviour of the gelator molecules in the gel state. In addition, variable-temperature DOSY NMR experiments were performed to determine the gel-to-sol transition. The PFG NMR experiments performed as a function of gradient strength were further analyzed using monoexponential…
Kinetics and equilibrium in insulin radioimmunoassay.
2002
The kinetics of insulin reaction has been studied with its specific antibody immobilized on the inner wall of the reaction tube; the radioimmunoanalytical determination of such a substance is based on the reaction. Independent variables were labelled and unlabelled insulin concentrations, temperature, viscosity, and the medium's ionic strength. Biexponential kinetics was found to be dependent on the concentrations fitted to the models discussed in the paper. The effect of temperature shows activation parameters similar to the viscous flow energy of water, which suggests that the reaction is diffusion-controlled. The results of the viscosity analysis points at the clearly negative influence …