Scattering from droplet microemulsions

Scattering from droplet microemulsions 2.2.1 General outline... 

In this subsection, the theoretical background for SANS and neutron spin-echo measurements carried out with o/w- and w/o-droplet microemulsions will be presented. According to Milner, Safran and others, shape fluctuations in droplet microemulsions can be described in terms of spherical harmonics [42-44]. This offers the possibility to calculate a dynamic structure factor S(q,w) or its Fourier transform, i.e. the intermediate scattering function I(q,t) for the problem, which can be used to analyse dynamical measurements by neutron spin-echo spectroscopy [45]. For the scattering from thin shells I(q,t) was calculated [43]... 

As already pointed out the first work directly measuring the deformation dynamics in an o/w-droplet microemulsion using NSE was published by Huang et al. [45]. In this work, a microemulsion based on the surfactant AOT was studied and it was shown that the intermediate scattering functions contain information about the centre of mass diffusion and in addition also contributions from the deformation dynamics. The intermediate scattering functions obtained in this work are shown in Fig. 2.3. 

Figure 2.3 Intermediate scattering functions obtained for an AOT-based o/w-droplet microemulsion using NSE. The solid lines are fits with a single exponential function yielding an effective diffusion coefficient. Note that this was the first NSE study of a microemulsion showing the calculation of k on the basis of the intermediate scattering functions. (From Ref. [45], reprinted with permission of the American Physical Society.)...

Figure 2.5 Relaxation rates F of the intensity correlation functions as a function of q2 obtained via a photon correlation spectroscopy experiment. The sample was a w/o-droplet microemulsion made of D2 0/n-octane-di8/CioE4. On the oil-continuous side of the phase diagram the scattered light intensity is usually low leading to rather large errors of the individual data points. Nevertheless, from the slope of the linear fit the translational diffusion coefficient is obtained. (Figure redrawn with data from Ref. [67].)...

Figure 2.6 Measured intermediate scattering functions of a w/o-droplet microemulsion for the system D2 0/n-octane-d- 8/CioE4. The four curves were obtained at four different q values close to the minimum of the droplet form factor. The solid lines are double exponential fits with only two adjustable parameters. The translational diffusion coefficient was determined using PCS (see Fig. 2.5) and used as input for the analysis of the NSE data. (Figure redrawn with data taken from Ref. [67].)...

The intensity and the autocorrelation function of light scattered by a microemulsion have been investigated for the water in oil type microemulsions. We studied two mixtures water-SDS-cyclohexane-pentanol and water-SDS-toluene-butanol. We obtain information about droplet size (radius of the aqueous core, hydro-dynamic radius) and about interaction forces between the droplets (from osmotic compressibility and diffusion coefficient data). 

Details are given of a number of indirect techniques for characterising droplet or particle sizes before and after PS polymerisation without diluting the system. Data from small angle neutron scattering on PS microemulsions are presented. 15 refs. 

Figure 18.4. Static light scattering from water-in-oil microemulsion droplets with the surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The normalized static scattering intensity < > is shown as a function of the...

The interpretation of the bulk properties of the microemulsions phases, close to Sx, in terms of critical phenomena, is then less satisfying. Near this boundary, the samples are further from a critical consolute point than in the case of the boundary S2. As far as bulk properties are concerned, light scattering experiments are rather sensitive to droplets elongation as it will be observed in viscosity measurements. 

The analysis of the light scattering data using CONTIN also allows for a determination of the size polydispersity of the microemulsion droplets, because all the moments u = / pm G(r)rndr which describe the distribution function G(T) are computed (for details see Ref. [98]). The polydispersity index is obtained from... 

Figure 7.8 Schematic scattering length density (sld or p x 1010 cm-2) profile fitted to SANS data from surfactant-stabilised D20-in-C02 microemulsion droplets. (From Ref. [55], reprinted with permission of Wiley-VCH Verlag GmbH Co. KgaA.)...

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