Small angle scattering techniques

This technique is quite commonly used to characterize microemulsions, providing information on domain size and spatial arrangement. Regev and co-workers (1996) characterized octaethylene glycol mono -dodecyl ether-dodecane-pentanol-water systems as a fire-resistant 

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Studies of thermally denatured proteins remain technically challenging owing to the propensity of thermally unfolded proteins to aggregate. Despite this potential difficulty, small-angle scattering techniques have been employed in the characterization of a number of thermally unfolded states. 

Unfortunately, the small-angle scattering techniques used in the investigations of Nafion morphology generally probe but a small region of reciprocal space and Fourier inversion methods of analyzing the... 

Nevertheless, small-angle scattering techniques are not very suitable for the study of lower dendrimer generations because such dendrimers yield only weak scattering signals and a high uncertainty factor therefore exists. SANS and SAXS experiments are not only costly, but also make substantial demands on time and require relatively large amounts of substances (several 100 mg). These methods are therefore out of the question for routine use, such as for the determination of the molar mass of dendrimers. 

The principal focus of interest has hitherto been on the group of flexible dendrimers, which embraces the major part of the dendrimers reported in the literature, also including the commercially available POPAM and PAMAM dendrimers having an aliphatic scaffold. In recent years valuable knowledge about the density profile, the three-dimensional structure, and the interactions of dendrimers in solution has been obtained with the aid of small-angle scattering techniques, as is apparent from the following overview. 

A more complete description of the crossover from two- to three-dimensional critical behavior, that incorporates the shift of Tc, Eq. (129), can be written down in terms of crossover scaling functions M for the order parameter M, Eq. (130) and S for the collective scattering intensity Scoll for scattering wavenumber q—>0, which can be accessed by small angle scattering techniques [186]. Defining =1—T/Tc (D->°o) we can write... 

In the present work the meso- and macro-structural characteristics of the mesoporous adsorbent MCM-41 have been estimated with the help of various techniques. The structure is found to comprise four different length scales that of the mesopores, the crystaUites, the grains and of the particles. It was found that the surface area estimated by the use of small angle scattering techniques is higher, while that estimated by mercury porosimetry is much lower, than that obtained from gas adsorption methods. Based on the macropore characterization by mercury porosimetry, and the considerable macropore area determined, it is seen that the actual mesopore area of MCM-41 may be significantly lower than the BET area. TEM studies indicated that MCM-41 does not have an ideal mesopore structure however, it may still be treated as a model mesoporous material for gas adsorption studies because of the large radius of curvature of the channels. 

The positron annihilation method like the small angle scattering techniques is suitable in characterization of closed pores which are inaccessible for adsorbate molecules in classic experiments, like adsorption, mercury intrusion or thermoporometry. 

Techniques have been developed to determine the fractal dimension of experimental aggregate particles in solution using small-angle scattering techniques, from x-ray, light, or even neutron sources. In these techniques the scattering intensity, I q), is proportional to the scattering vector, q, raised to the mass fractal dimension by ... 

A model of structure has been developped from electron microscopy and X-ray studies in Nafions (6). No basic difference exists between X-ray and neutron techniques. Nuclear interactions of neutrons with matter are characterized by the coherent scattering length and the corresponding values for H and D are very different Because of the different origins of the contrast, X-ray and neutron small angle scattering techniques are complementary. 

Small-angle scattering techniques (small-angle x-ray and neutron scattering) have recently become established as versatile probes for the determination of structures of porous solids [46,47]. The size, shape, concentration, and surface area of inhomogeneities, such as pores, can be studied. 

Small-angle scattering has been the subject of numerous books and reviews and so the reader who wishes to have more precise information will find illuminating and complete discussions in books devoted either to small-angle scattering techniques or to the thermodynamics of polymers in solution [12-16]. 

After the initial DLS studies were complete, it became apparent that the very strong interdroplet attractive interactions in near-critical and supercritical fluids limited the standard DLS technique to systems of higher dilution or to high fluid densities. Thus, small-angle scattering techniques were later used to better resolve the full dimensional scale range of these microemulsions over a wider range of conditions. 

In this review, we have provided a selective overview of theoretical and experimental studies on kinetic processes in block copolymer micellar systems. We have demonstrated the strengths of time-resolved small-angle scattering techniques by highlighting recent examples from the literature. Most of the available literamre in this field is either related to equihbrium exchange kinetics or micellization kinetics. 

Small-angle scattering techniques have been applied to polysiloxane materials. One important example is the characterization of fillers introduced into polysiloxane elastomers, or the reverse, the incorporation of such elastomers into ceramic matrices (in both cases to improve mechanical properties). - Another example is characterization of the anisotropy induced by strain in silica-PDMS composites. Chapter 9 describes some of this work. Elastic neutron scattering can be illustrated by the characterization of polysiloxane blends, and quasielastic neutron scattering by studies of the dynamics of PDMS. There have also been Monte Carlo calculations of PDMS particle scattering functions, including how they varied with chain length, chain structure, and temperature. ... 

Another instance where SAXS has been a useful tool for polymer characterization relates to the examination of block copolymers. Block copolymers can form structural domains that are on length scales detectable by the small angle scattering technique. A series of scattering peaks occur with each peak position having a separation indicative of the stmcture formed. Examples of this would be if a peak occurred at 2 = 1 A , reflections would occur at 2,3,4,5,... for lamellar domains, whilst body centred cubic will have peak positions V2, VS, V4, V5,... (Hamley and Castelletto 2004). 

SMALL-ANGLE SCATTERING TECHNIQUES (SANS AND SAXS)... 

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