Mean distance of closest approach of ions: Lithium salts in aqueous solutions

Numerical values for the mean distance of closest approach of ions, "a", for lithium salts in aqueous solutions are presented and discussed. These values were obtained from both experimental activity and diffusion coefficients, and estimated by using different theoretical approaches.http://www.sciencedirect.com/science/article/B6TGR-4RR1NKM-1/1/b8d3cdac33991c5424d567940bc0c3a

Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.http://www.sciencedirect.com/science/article/B6TWW-4DVBFCN-7/1/63e48f8aac1513c35feeaa6c746621e

Combined sorption/transport of sodium dodecyl sulfate and hydrochloric acid in a blend of cellulose acetate butyrate with cellulose acetate hydrogen phthalate

The transport of hydrochloric acid (0.001-0.1 M) and sodium dodecyl sulfate (0.001-0.1 M) has been measured through a membrane consisting of a blend of cellulose acetate butyrate and cellulose acetate hydrogen phthalate. The cellulose derivative blend is suggested to suffer an alteration in the degree of hydrophobicity when in equilibrium with sodium dodecyl sulfate (SDS) through hemimicelle formation. An increase in surface hydrophobicity of the blend when in equilibrium with SDS solution was observed by fluorescence measurements using the vibronic bands of the probe pyrene, as well as by water desorption kinetics; a decrease of the effective diffusion coefficients from 1.2 × 10-11 m2 s-1 in the absence of SDS to approximately 2 × 10-13 m2 s-1 in its presence was found. The value obtained for the mutual diffusion coefficient of HCl in the concentration range 0.001-0.1 M (D=4.2×10-14 m2 s-1) shows also that the membrane presents hydrophobic features. The flux of SDS in the blend membrane at different pH values shows two distinct permeation rates depending on the cmc. However, from the calculation of permeability coefficients at SDS concentrations below the cmc a clear decrease in P is found, whilst, at concentrations above the cmc the permeability coefficients are nearly constant, only showing a slightly increase. The diffusion coefficients of SDS in the blend increase over the whole SDS concentration range analysed and show an effective diffusion coefficient 2-3 orders of magnitude below the diffusion coefficients of SDS in aqueous solutions. This fact suggests that the only diffusing species are SDS unimers. The presence of HCl in the SDS bulk solution has the effect of increasing the permeability and diffusion coefficients. Mutual analysis of permeation and diffusion coefficients and sorption isotherms shows that, on decreasing the pH, the interactions between SDS and the polymer network decrease. This is also reflected in a clear decrease of the hydrophobic interactions between the diffusing and polymeric species, provoked by a decrease in the unimer-unimer association.http://www.sciencedirect.com/science/article/B6TWW-49WPFVC-K/1/a590044f98d090805ffa5445fba983a

Effect of different electrolytes on the swelling properties of calyx[4]pyrrole-containing polyacrylamide membranes

Calix[4]pyrrole (1) was synthesized and characterized and this macrocycle was incorporated in polyacrylamide gels. The presence of meso-octamethyl-porphyrinogen inside of gel was checked using infrared spectroscopy, differential scanning calorimetry, and swelling studies. The swelling degree of these hydrogels in equilibrium with different electrolytes (NaCl, LiCl, KCl, CaCl2 and AlCl3) was measured in a concentration range 0.1-0.5 mol dm-3. Although no significant alterations in the swelling degree can be found for the different 1:1 electrolytes, when the cation charge of unsymmetrical electrolytes increases, the gel swells in a significant way. This swelling process is enhanced by the presence of calyx[4]pyrrole. The effect of alkaline hydrolysis of polaycrylamide-based hydrogels was also studied. The hydrolysed hydrogels collapse in the presence of the electrolytes; this behavior is dependent on the hydrolysis degree, electrolyte charge and calyx[4]pyrrole presence and concentration; the latter leads to polyacrylamide with tailor-made properties.http://www.sciencedirect.com/science/article/B6TWW-4K0FJT9-2/1/a2e10fed9f08e8248532610bc3e2bdc

Aggregation and micellization of sodium dodecyl sulfate in the presence of Ce(III) at different temperatures: A conductometric study

Aggregation properties of sodium dodecyl sulfate (SDS) in the presence of cerium(III) chloride, at various temperatures (298.15-323.15 K) have been measured by the electrical conductance technique. The experimental data on aqueous solutions as a function of SDS concentration show the presence of two inflexion points indicating the presence of two distinct interaction mechanisms: the first, occurring at SDS concentrations below the critical micelle concentration of the pure surfactant, which can be explained by the formation of aggregates between dodecyl sulfate (DS-) and Ce(III), while the second one, at SDS concentrations around the critical micelle concentration (cmc) of the pure surfactant which is due to the SDS micellization. The aggregation between DS- and Ce(III) was confirmed by static light scattering. The binding ratio of DS-/Ce(III) changes from 6 to 4, shows a slight dependence on the Ce(III) concentration and is independent of the temperature. The thermodynamic micellization parameters, Gibbs energy, enthalpy and entropy of micellization were calculated on the basis of the experimental data for the aggregation concentration, and the degree of counterion dissociation of the micelles. The SDS micellization is energetically favoured by increasing either the concentration of CeCl3 or the temperature. Such behaviour is clearly dominated by a decrease of the micellization (exothermic) enthalpy. The entropy of micellization approaches zero as the cerium(III) chloride concentration and temperature increase.http://www.sciencedirect.com/science/article/B6WHR-4S6G90R-1/1/a864220de360ed7b600885de2f94b11

Observation of the Bc+→J/ψπ+π0B_c^+ \to J/\psi \pi^+ \pi^0 decay

The first observation of the $B_c^+ \to J/\psi \pi^+ \pi^0$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the $B_c^+ \to J/\psi \pi^+$ channel is measured to be $$\frac{ {\cal{B}}_{( B_c^+ \to J/\psi \pi^+\pi^0 ) }} { {\cal{B}}_{( B_c^+ \to J/\psi \pi^+ ) }} = 2.80 \pm 0.15 \pm 0.11 \pm 0.16 \,,$$ where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for $B^+ \to J/\psi K^{*+}$ and $B^+ \to J/\psi K^+$ decays, which are used to determine the $\pi^0$ detection efficiency. The $\pi^+\pi^0$ mass spectrum is found to be consistent with the dominance of an intermediate $\rho^+$ contribution in accordance with a model based on QCD factorisation.The first observation of the ${B}_c^{+}\to J/\psi {\pi}^{+}{\pi}^0$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9 fb$^{−1}$, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the ${B}_c^{+}\to J/\psi {\pi}^{+}$ channel is measured to be$\frac{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}{\pi}^0}}{{\mathcal{B}}_{B_c^{+}\to J/\psi {\pi}^{+}}}=2.80\pm 0.15\pm 0.11\pm 0.16,$where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for B$^{+}$ → J/ψK$^{*+}$ and ${B}_c^{+}\to J/\psi {\pi}^{+}$ decays, which are used to determine the π$^{0}$ detection efficiency. The π$^{+}$π$^{0}$ mass spectrum is found to be consistent with the dominance of an intermediate ρ$^{+}$ contribution in accordance with a model based on QCD factorisation.[graphic not available: see fulltext]The first observation of the $B_c^+ \to J/\psi \pi^+ \pi^0$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the $B_c^+ \to J/\psi \pi^+$ channel is measured to be $$\frac{ {\cal{B}}( B_c^+ \to J/\psi \pi^+\pi^0 ) } { {\cal{B}}( B_c^+ \to J/\psi \pi^+ ) } = 2.80 \pm 0.15 \pm 0.11 \pm 0.16 \,,$$ where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for $B^+ \to J/\psi K^{*+}$ and $B^+ \to J/\psi K^+$ decays, which are used to determine the $\pi^0$ detection efficiency. The $\pi^+\pi^0$ mass spectrum is found to be consistent with the dominance of an intermediate $\rho^+$ contribution in accordance with a model based on QCD factorisation