M. Terenzi

A study of stability of plasticized PEO electrolytes

Abstract Considerable research effort has been devoted to lowering the useful operating temperature of PEO–LiX polymer electrolytes to the ambient region. The most common approach has been that of adding liquid plasticizers, such as ethylene carbonate (EC) or propylene carbonate (PC), to the PEO–LiX matrix. In this paper, we have extensively studied EC plasticized LiCF 3 SO 3 ·P(EO) 10 and LiClO 4 ·P(EO) 10 , measuring the conductivity, thermal characteristics and X-ray diffraction patterns of the electrolyte films. A very significant feature of the results is that the enhanced conductivity of the as-prepared films is transient and is not maintained on thermal cycling under vacuum. The systems are not thermodynamically stable due to a loss of the bulk of the plasticizer and this will impair their applications in devices.

Gemini surfactant–water mixtures: some physical–chemical properties

Abstract The phase diagram of the water-Gemini 16-4-16 system has been investigated and the phase boundaries were determined. DSC and optical microscopy were used to define the region of existence of the different phases. No liquid crystalline phases have been observed, however, a two-phase region and a wide gel phase follow the solution region. The solution region can be highly viscous, depending on composition and temperature. Surface tension and electrical conductance experiments have been performed, to define micelle formation and counter-ion binding to micelles. Interactions and motions over short distances were studied by 1H-NMR relaxation experiments. The drastic decrease of spin–spin relaxation time, T2, with Gemini composition ( ≈2 wt.%) was explained in terms of particle growth. Pulsed field gradient spin-echo (PGSE) NMR experiments were used to determine water and surfactant self-diffusion. Some modifications in the micellar structure were inferred on increasing the Gemini content in the mixture. Dynamic rheological experiments were performed for probing the solution microstructure. The observed high solution viscosity and the shear relaxation processes were rationalized in terms of the presence of entangled threadlike aggregates at a moderate concentration (≈ 4 wt.%). According to the Bohlin theory of flow as a cooperative phenomenon, the number of the micellar aggregates correlated to each other, and the interaction strength between the micellar units was obtained as a function of Gemini concentration.

Self-diffusion of water in a lamellar lyotropic liquid crystal: A study by pulsed field gradient NMR

Abstract The self-diffusion of water has been measured in unaligned Lα mesophases of potassium palmitate and water, using the pulsed field gradient NMR technique (PFG NMR). The experimental data have been interpreted in terms of a structural factor and of the stoichiometric compositions of the analyzed mixtures.

Studies of ionic motion in perovskite fluorides

In this paper we report the results of ionic conductivity and of nuclear magnetic resonance, (N.M.R.) relaxation studies of the systems NaMgF3, KMgF3 and KCaF3. Detailed studies of KCaF3 single crystals show that the F− ion is mobile in these systems even at room temperature. At low temperatures the conductivity and N.M.R. results suggest extrinsic behaviour, the F− motion being dominated by residual impurities. Fast-ionic conduction is observed at high temperatures. In crystals deliberately doped with oxygen the compensating defect is expected to be the F− vacancy. The results of conductivity and N.M.R. are consistent with a vacancy diffusion mechanism and its activation energy was determined. Similar experiments for NaMgF3 and KMgF3 revealed no detectable F− ion motion even at high temperatures.

Analysis of water self‐diffusion in polycrystalline lamellar systems by pulsed field gradient nuclear magnetic resonance experiments

A study of the water self‐diffusion in polycrystalline lamellar systems, by pulsed field gradient spin‐echo (PFG‐SE) nuclear magnetic resonance (NMR) experiments, is reported here. Our analysis confirmed the validity of previous equations for bidimensional water self‐diffusion in lamellar lyomesophases and clarified their applicability limits. Depending on the diffusion experimental time range, two different procedures can be built up; for wide amplitude windows, the experimental diffusion coefficients are correlated to the fraction of bound water, whereas for short times it has been possible to point out the ‘‘obstruction factor’’ to diffusion. Experimental support for the theoretical findings was inferred by investigation of the lamellar mesophase of the binary system water/sodium‐bis‐2‐ethylhexyl sulfosuccinate (AOT). It confirmed the existence of some defects in the lamellae at water concentration higher than 70 wt. %.

Studies on krafft point solubility in surfactant solutions

Abstract The thermal transitions from dispersed solid state to micellar solutions were studied for ionic surfactants in binary and pseudobinary aqueous surfactant systems. Particular attention was focused on the region close to the Krafft point, T k . The experimental results are interpreted in thermodynamic terms by adopting a phase separation model for micelle formation.

Water diffusion and phase transition investigation in lyotropic mesophases. A NMR study

Abstract Measurements of water diffusion in non-aligned lyotropic mesophases have been made using the pulsed field gradient NMR technique (PFG-NMR). The investigated systems were mixtures of potassium palmitate and water (KP/H2O). Deuterium nuclear magnetic resonance spectral profiles (D-NMR) were also analyzed on perdeuterated potassium palmitate. Experimental data were taken in the Hα mesophase, the Lβ mesophase and in the intermediate region of the phase diagram between the Lα and Hα mesophases. The results are discussed in terms of the mixture composition and of the amphiphilic aggregate structures. The behavior of the water diffusion at the phase transition ocurring between the Lβ and Hα mesophases suggests a new insight on the evolution of this transition across the two phase regions. Furthermore the lyotropic mesophase ocurring in the intermediate region has been identified.

NMR Investigation of the Lamellar Mesophase Occurring in the System Aerosol OT-Water

Abstract The lamellar mesophase occurring in the system water aerosol OT (AOT) has been studied by combining nuclear magnetic resonance methods, such as deuterium quadruple measurement (D-NMR) and pulsed field gradient (PFG-NMR), with optical microscopy. At low AOT content the mesophase shows a biaxial character and consists of defective structures, which have been interpreted as rippled lamellae. In the range between 20 and 28 AOT wt% the mesophase is a mixture of regular and rippled lamellae; for larger AOT content the system can be considered a normal lamellar mesophase. The system is strongly influenced by mechanical effects, which force the lamellae to assume defective configurations. Quadrupole splittings have been analyzed in terms of a “ripple model” and the angle of ripple deformation has been obtained.

Water self-diffusion in micellar solutions and in lyotropic mesophases of the system water/Triton TX-100

AbstractStudies by Pulsed Field Gradient NMR (PFG-NMR) methods and other physico-chemical experiments have been used to clarify the processes connected with water self-diffusion in mixtures formed by water and Triton TX-100. In micellar solutions the solvent diffusive trend is related to micelle hydration and, to a much less extent, to micelle size and shape. Hydration numbers from PFG-NMR are close to those obtained by viscosity experiments. In solution phases of the reversed kind, water in oil, water self-diffusion data suggest that aqueous domains are large and bicontinuous. Water self-diffusion in the hexagonal lyotropic mesophase has been interpreted by introducing a geometrydependent contraint,