Small-angle neutron scattering index

The micelle formation process and structure can be described by thermodynamic functions (AG°mjc, AH°mjc, AS°mic), physical parameters (surface tension, conductivity, refractive index) or by using techniques such NMR spectroscopy, fluorescence spectroscopy, small-angle neutron scattering and positron annihilation. Experimental data show that the dependence of the aggregate nature, whether normal or reverse micelle is formed, depends on the dielectric constant of the medium (Das et al., 1992 Gon and Kumar, 1996 Kertes and Gutman, 1976 Ward and du Reau, 1993). The thermodynamic functions for micellization of some surfactants are presented in Table 1.1. 

The ability to manipulate the neutron refractive index, through D/H isotopic substitution, makes neutron reflectivity and small angle scattering powerful techniques for the study of surfactant mixtures, and this has been extensively exploited in the study of adsorption at the air-water interface [17] and in micelles. 

Polymer conformations are studied by various scattering experiments (light, small-angle X-ray and neutron scattering). These techniques are based on the contrast between the polymer and the surrounding media (solvent in the case of polymer solutions and other polymers in the case of polymer melts or blends). The contrast in light scattering arises from differences in refractive index between polymer and solvent, and the scattered intensity is proportional to the square of the refractive index increment dn/dc [see Eq. (1.86)]. 

Fig. 43a. Neutron small angle scattering intensity I(q) plotted vs q for three temperatures T above Tmst (main graph), for a polyethylenepropylene(PEP) — polyethylethylene(PEE) diblock copolymer, with f = 0.55, molecular weight Mw — 57.500, polydispersity index Mw/Mn = 1.05. The microphase separation transition occurs for Tmst = 125°C. For further explanations cl Textb Inverse peak intensity I (q ) dotted vs inverse temperature.The full curve is a one-para meter fit to the theoty of Fredrickson and Helfand [58], while Leibler s [43] prediction for the intensity at the transition is marked as mean field theory . From Bates et al. [317]...

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