Scattering techniques 1072 / Subject

Sucrose is subjected to the action of the bacterium Leuconostoc mesenteroides B 512 and the crude, high-molecular weight dextran thus formed is hydrolyzed and fractionated to an average molecular weight of about 40,000 as measured by light-scattering techniques. 

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

Bending moduli can in principle be obtained for two types of systems (i) extended, flat surfaces or interfaces, the subject matter of this section, and (ii) surfaces that are already strongly curved, and for which y is zero or extremely low, such as in vesicles or micro-emulsions. For instance such moduli can be inferred from shape fluctuations, from the Kerr effect (sec. 1.7.14] or from polydispersity using some scattering technique. We repeat that this type of measurement is often ambiguous because the bending contributions to the Helmholtz energy can only be estimated when all other contributions are accurately known. 

The structure, however, is not static but is subject to thermally driven fluctuations. The local structure changes continuously as a function of time due to orientational and translational molecular motions. The time scale of these motions may range from nanoseconds up to several hundred years. The structure of the amorphous state as well as its time-dependent fluctuations can be analysed by various scattering techniques, such as X-ray, neutron, electron and light scattering. 

Finally, in this historical introduction, we should recall that neutrons have been the subject of two Nobel Prizes to J. Chadwick for the discovery of the neutron (1935) and to B.N. Brockhouse and C.G. Shull (1994) for their pioneering contributions to the development of neutron scattering techniques (inelastic scattering and diffraction respectively). 

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]. 

Besides pcs, other light scattering techniques including Brillouin scattering and Fabry-Perot interferometry described in previous sections have been applied to probe the dynamics of polymers at higher frequencies than the more conventional techniques. Interpretations of the results from these techniques are still subjects of controversy and are not discussed here. 

For XAS a high intensity continuous X-ray spectrum is required which is most conveniently generated on a synchrotron radiation source. There are several excellent text books, at both introductory as well as advanced level, available on the theory and general application of synchrotron radia-tion and therefore we will only treat the most relevant details required for the combinations of spectroscopy and scattering techniques, which is the subject of this manuscript, here. 

X-ray, electron and optical scattering techniques and a range of other analytical tools are commonly applied to determine the structure of polymers. X-ray diffraction, for example, permits the determination of interatomic ordering and chain packing. The morphology of polymers is determined by a wide range of optical and electron microscopy techniques, which are the major subject of this text. Finally, there are many other analytical techniques that provide important information regarding polymer structure. 

The model of CM has recently been adapted by Miroshnychenko and Clarke [83] to predict enhanced scattering from entangled polymer solutions subjected to oscillatory flow, and a reasonable agreement between predictions and experiments [84] was found. This highlights the importance of scattering techniques in this field - they permit a quantitative comparison between theory and experiment. 

Scattering phenomenons form the basis of techniques used for the characterization of semicrystalline synthetic polymers and the elucidation of the chemical structure of crystalline biopolymers, such as proteins. Moreover, the size, shape and state of aggregation of macromolecules in solution can be determined using X-ray scattering techniques. This subject has been covered extensively elsewhere [24-54]. 

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