R. Giordano

Temperature and concentration dependence of SANS spectra of aqueous solutions of short-chain amphiphiles

The small-angle neutron scattering (SANS) of some aqueous solutions of short-chain amphiphiles (glycols, diglycols, diols) has been measured as a function of concentration and temperature. The analysis of the spectra in terms of the Teubner-Strey phenomelogical formula indicates that, on increasing the concentration of the amphiphile, the structure of all these systems evolves in a similar way, i.e. a transition from disordered structures toward correlated aggregates (microstructures). The transition is depressed by increasing the temperature.

Hydrogen-bond effects induced by alcohol on the structure and dynamics of ionic reverse micelles

Abstract In this work we report how the structure of Zn(AOT)2/H2O/d-cyclohexane microemulsions is affected by the presence of alcohol (normal pentanol) molecules as cosurfactant. The systems are investigated by small-angle neutron scattering (SANS) and by Fourier transform IR (FTIR) spectroscopy. The SANS technique allows the study of the evolution of the size, the shape and the possible correlation length of concentration fluctuations as a function of water and alcohol content. Moreover FTIR spectra, in the OH stretching region, is quite sensitive to the structural changes of the water, induced by the polarization effects of the polar heads of the micelle surface and the positive counterions and by the presence of the alcohol.

Structural properties of micellar solutions

Abstract The results of a small angle neutron scattering experiment are reported in which the structural properties of a novel water/AOT/cyclohexane reverse micelle system is investigated. The metallic ions bound to AOT are Al 3+ and Zn 2+ . Spectra were collected at different water contents and at the maximum surfactant concentration. A quantitative evaluation of the shape and size of the droplets formed is performed, and a comparison among similar shapes is presented.

SANS study of a fluorinated water-in-oil microemulsion

The experimental results of a SANS analysis of fluorinated water-in-oil microemulsions with perfluoropolyether oil and surfactant are shown at T = 20°C and T = 35°C for samples with a constant water-to-surfactant molar ratio WS = 11. Under the hypothesis that the system is composed of interacting droplets, by a Guinier analysis of the dilute samples, a droplet radius of 23 A is found for the two temperatures studied. Furthermore, all the samples studied follow the Porod law, as expected for dispersed particles with a sharp interface. For the two temperatures studied, a microemulsion interfacial area per surfactant molecule of 50 A2 is found in the dilute region and about 35 A2 in the concentrated region.

QELS and SANS studies of octyl-β-glucoside micellar solutions

Abstract Quasi elastic light scattering (QELS) and small angle neutron scattering (SANS) measurements were performed on micellar solutions of octyl-β-glucoside in water and in water+glycine mixtures. The comparison of the experimental results obtained with both the techniques indicates that the micelles are rod-like also at concentration values very close to the critical micellar concentration (cmc). The behaviour of the diffusion coefficient, obtained from QELS data, as a function of temperature and concentration has been interpreted in the frame of the current theories and it was found to be consistent with SANS results. The micelles seem to be monodispersed in the investigated concentration range and do not increase their dimension with concentration. The addition of glycine seems to not play an important role in the determination of micellar size, although its presence in solution shifts the cmc towards lower concentrations.

Complexation of counter-ions in ionic micellar solutions: a small-angle neutron scattering study

Abstract The properties of LDS and SDS micellar solutions upon the addition of [2.2.2]-cryptand (C222) are studied by small-angle neutron scattering (SANS). The interfacial thickness of the micelle for three ligand to surfactant molar ratios ( L S = 0.5, 1.0 and 1.5 ) increases from 5.5 A (interfacial thickness of the micelles without ligand) to 10 A, indicating that the ligand is located at the interface. The micellar net surface charge and the average aggregation number decrease as L S increases, producing a slight decrease of the micellar size and a more spherical shape. The ionization degree of the LDS micelles is almost constant as L S increases, whereas it decreases slightly for SDS micelles. This supports the higher binding ability of C222 for sodium ions. The liogand/surfactant molar ratio at the interface is at most 1 2 when the ligand is added to the surfactant solution (LDS and SDS) in equimolar amounts. This implies that only half of the total amount is partitioned at the interface, while the remaining ligand molecules are in the bulk solution. Further addition of the ligand increases its amount in the bulk solution.

Porosimetric and particle-size measurements by small-angle neutron scattering

A small-angle neutron scattering (SANS) study was carried out on typical building stones widely used in north-eastern Sicily in several architectonic contexts, aimed at measuring the particle and pore-size distribution in view of stone treatment by protective (Hydrophase) and/or consolidant (Ethyl silicate) agents. Samples of quartzite, sandstone, calcarenite and marble exhibit particle and pore-size dimensions that are inversely proportional to the porosimetric values of the stones. The particle size of treated stones varies in an analogous way to the grain size of the blank samples. The present paper aims to find a correlation between particle size and porosity in building stones used in ancient monuments. The relationship between particle size and porosity is investigated using SANS techniques, which are applied to characterize the physical, mechanical and thermal behaviour of single mineral grains belonging to different lithologies.

SANS Studies of Octyl-β-glucoside and Glycine Micellar Solutions

Small-angle neutron scattering (SANS) experiments were performed on micellar solutions of octyl-β-glucoside (OBG) in water and on solutions of OBG + glycine in water. A detailed analysis of the results obtained for different concentrations (from 0.026 to 1 M) of glycine and OBG shows that: (i) the structure of the micelles of OBG is always ellipsoidal with the long axis increasing as the concentration of OBG increases from the critical micellar concentration (c.m.c. = 0.022 M) to 1 M; (ii) there is a tendency to form aggregates at concentrations of OBG smaller than 0.5 M; (iii) steric repulsive interactions are clearly seen for concentrations above 0.6 M. The virial coefficient is evaluated as a function of the concentration in OBG. The negative values at low concentration reveal the presence of attractive interactions, while at high concentration the repulsive steric interaction dominates. At high concentration of OBG, the spectra with or without glycine are the same. The analysis shows that glycine remains in water and that its presence does not affect the structure of the micelles.

SANS on fluorinated water-in-oil microemulsions

Abstract Preliminary SANS results on water-in-oil microemulsions composed of water, fluorinated surfactant and fluorinated oil, indicate that the system is composed of interacting droplets in a large range of compositions. Work is in progress to find the interaction potential.

Quasi-elastic neutron scattering of hydrated myoglobin

Abstract Some preliminary results are reported concerning the dynamics of hydration water on the surface of myoglobin, investigated by incoherent quasi-elastic neutron scattering. Several samples of protein were studied at a water content of h = 0.1, 0.4 and 0.8 g/g. A lineshape analysis of the spectra provided the half-width and the elastic incoherent structure factor for the water contribution in the scattered intensity. At very low hydration, water molecules seemed to perform only rotational motion, whereas at greater hydration a diffusional motion, inside confined regions of about 6, took place.