1,721,060 research outputs found
Calorimetric Study of PAS-C2 and PAS-C3 Distribution in Micellar Solutions of PAS-C7 at Different pH
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Aqueous Solution of N-alkyll-Nicotinamide Chloride Surfactants: Thermodynamic Properties
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Temperature dependence of enthalpic properties of aqueous micellar solution of some N-alkylnicotinamide chloride surfactants
No full textThe dependence on the temp. of the enthalpic properties of some nicotinamide derivs. was studied by measuring the heats of diln., using an LKB flow microcalorimeter. The measurements were performed at 10, 18 and 40° in the case of N-nonylnicotinamide (C9NAC) and N-decylnicotinamide chloride (C10-NAC) and at 40° for N-heptylnicotinamide chloride (C7-NAC). An increase in the temp. produces a lowering of enthalpic curves vs. m that is directly proportional to the temp. change. By assuming a const. heat capacity in the temp. range examd., the trends of heat capacities vs. m through the finite ratios Δ.vphi.L/ΔT were derived. These trends confirm the presence of a rearrangement in the micellar structure at ca. 0.35 mol/kg for C9-NAC and 0.25 mol/kg for C10-NAC, in agreement with the behavior of the terms with eight and 12 carbon atoms, previously studied. A pseudo-phase-transition model was assumed, in order to ext. the enthalpy of micellization at each temp. From the linear dependence of the enthalpy changes for the micellization process vs. temp., the std. heat capacities of micellization were evaluated as -299 J/K.mol for C9-NAC and of -385 J/K mol for C10-NAC. For the class of compds. under investigation, a group contribution to micellization heat capacity for each CH2 group, of -62 J/K mol was derived
Diffusion processes in amphiphilic aggregate systems
No full textThe diffusion properties of aggregates of amphiphilic mols. (e.g., micelles, microemulsion) are discussed. The interaction of these organized assemblies with water-sparingly sol. org. compds. and ions and the consequent influence on the transport of these species is examd. as well as their effect on the transfer of solutes through a membrane
Host-guest Chemistry in the Gas Phase and at the Gas-solid Interface: Fundamental Aspects and Practical Applications
No full textThe study of host-guest interactions has recently expanded from solution chemistry to the gas phase, where solvent effects are not present, allowing better understanding of the intrinsic phenomena responsible for molecular recognition. Important aspects under investigation include the mechanism of interaction, the identification of binding groups, as well as the discovery of structural requirements for the host to undergo inclusion complexation. The information gained from these gas phase studies can be exploited to design new practical applications of host-guest chemistry, particularly when gas-solid interactions are involved. Analytical devices such as gas sensors and chromatographic adsorbing cartridges take advantage of the structural recognition capability of the host to achieve high levels of selectivity
Aqueous micellar solutions of some N-alkylnicotinamide and N-alkylpyridinium halide surfactants: apparent and partial molar enthalpies
No full textIn order to acquire thermodn. data for aq. solns. of functionalized surfactants, and to study the effect of the amidic group in the polar head and of the counterion, the enthalpies of diln. at 25° of N-alkylnicotinamide chlorides (alkyl chain length 7.9 or 10 carbon atoms), N-alkylpyridinium chlorides (alkyl chain length 8, 10, or 12 atoms), N-octylpyridinium bromide and N-decylpyridinium bromide were measured by means of a flow microcalorimeter. From the exptl. data, apparent and partial molar relative enthalpies as function of the molaity of the surfactant were derived. The amidic group in the nicotinamide compds. greatly enhances the hydrophobicity relative to the pyridinium compds. For cationic surfactants with the same alkyl chain, the trends of the molar enthalpies vs. concn. can be explained in terms of charge localization on the polar head. For the compds. under investigation, enthalpic data are not able to show phase transitions in the micellar region, but they confirm the role of the counterion in the energetics of micellar soln. The thermodn. functions of micellization were evaluated on the basis of the pseudo-phase transition model by graphical extrapolation
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