X-ray and neutron reflectivity for the investigation of polymers

The application of the specular reflection of neutrons to the study of surface and interfaces is described. The theoretical and experimental background to the technique is presented. A range of recent experimental results in surface chemistry, solid films and surface magnetism is discussed. In surface chemistry the results include adsorption of surfactants at the air-solution interface, insoluble monolayers and polymers at the air-liquid interface, soap films and adsorption at the liquid-solid and liquid-liquid interfaces. In solid films results on Langmuir-Blodgett films, hard carbon films, polymer films and some semiconductor layers are discussed. In surface magnetism experimental data which illustrate the nature of magnetism in magnetic multilayers and ferromagnetic films, and which describe flux penetration in superconductors, are presented.

https://iopscience.iop.org/article/10.1088/0953-8984/2/6/001/pdf

The application of the specular reflection of neutrons to the study of surfaces and interfaces

A variety of characterization methods based on X-ray scattering may be used to sensitively probe the structure of polymer surfaces and interfaces. Among these are small angle scattering in transmission, specular reflectivity, grazing incidence off-specular scattering, and grazing incidence diffraction. X-ray measurements provide information on electron density differences across interfaces, total interfacial area and volume fraction of a dispersed phase, microroughness of sharp interfaces, interface width, parameters of near-interface electron density profiles, and in-plane ordering in thin films and near surfaces. This review focuses on experimental aspects of the methods as analytical techniques, considering the relative merits of different approaches, and reviewing some recent measurements not yet reviewed elsewhere. Particular attention is given to the rapidly growing fields of specular reflectivity and off-specular scattering. After discussing general theoretical concepts applicable to all t...

X-Ray Scattering Methods for the Study of Polymer Interfaces

In the last 15 years there have been a number of observations of surfactants adsorbed at the air–water interface with structures more complicated than the expected single monolayer. These observations, mostly made by neutron or X-ray reflectivity, show structures varying from the usual monolayer to monolayer plus one or two additional bilayers to multilayer adsorption at the surface. These observations have been assembled in this article with a view to finding some common features between the very different systems and to relating them to aspects of the bulk solution phase behavior. It is argued that multilayering is primarily associated with wetting or prewetting of the air–water interface by phases in the bulk system, whose structures depend on an overall attractive force between the constituent units. Two such phases, whose formation is assumed to be partially driven by strong specific ion binding, are a concentrated lamellar phase that forms at low concentrations and a swollen lamellar phase that is n...

Multilayering of Surfactant Systems at the Air–Dilute Aqueous Solution Interface

A new direction in the field of x-ray optics is discussed. This new direction is associated with diffraction at grazing angles of incidence and diffraction; it is associated with the excitation of x-ray surface waves and quasiwaveguide modes, and with the study of the angular and energy dependences of the reflection spectra. An analysis of theoretical and experimental investigations in this area is carried out with the aim of determining the possibility of using these diffraction and reflection features for the study of surface layers, thin films and interfaces. The extremely asymmetric two- and multiwave diffraction schemes and the two-wave symmetric noncoplanar diffraction scheme are analyzed, as is the anomalous reflection of the x-rays. The angular dependences of the anomalous reflection are calculated on the basis of a model of a nonuniform surface layer. It is shown to be possible to use the angular dependence of the reflection for the determination of the statistical characteristics of surface nonuniformities. Experiments for the determination of short range order in surface films on the basis of the analysis of the extended fine structure of reflection spectra are discussed.

X-ray optics of surfaces (reflection and diffraction at grazing angles of incidence)

A theory has been developed which relates the intensity of the non-specular scattering of X-rays from thin films to the correlation function for the local deviation of the dielectric constant of the film from its average value. The theory predicts the positions and intensities of the maxima and minima in the distribution of the non-specularly scattered radiation as well as the existence of the non-specular `anomalous surface reflection' first reported by Yoneda. The results of an experimental study with thin copper films were in good agreement with the theory.

J. B. Bindell

Papers

The non‐specular scattering of X‐rays from thin films