Multicomponent polymer materials morphology

Interpenetrating polymer networks are defined eis a combination of two polymers, each in network form. From a practical point of view, an IPN is comprised of two polymers which cannot be separated chemically, do not dissolve or fiow, and are not bonded together. Like most other multicomponent polymer materials, IPN s usually phase separate due to their very small entropy of mixing. However, the presence of the crosslinks tends to reduce the resulting domain size, hence yielding a unique method of controlling the final morphology. 

A powerful method of examining the morphology of many multicomponent polymer materials utilizes transmission electron microscopy [Woodward, 1989]. If the two phases are nearly equal in electron density, staining with osmium tetroxide or other agents can be used. For more detailed discussion on the methods of morphology characterization, see Chapter 8. 

Multicomponent polymeric materials with microheterogeneous mophologies include a number of polymer blends and block copolymers, however, an especially easy way to bring about the desired morphology is through interpenetrating polymer networks. Several papers in the symposium are concerned with IPN s and related materials. 

Basics in Phase Morphologies of Multicomponent Polymer-Based Materials... 

Michler [2] has nicely summarized and realized practical examples of some of the modern tools of microscopy used to study the morphology and microstructure of polymers and polymer-based materials. The most frequently employed microscopic tool remains the scanning electron microscope. It is the fastest and allows one to reach interesting dimensions in multicomponent polymer blends and composites. Transmission electron microscopy can be ranked in the second position, whereas the optical microscope is usually used as a "first-check tool" before deeper investigation. It is nevertheless the strategic tool employed in life science (biomedical, Wlogics, etc.). In all these cases the sample preparation step is crucial before investigating the material s microstructure. 

To increase our understanding of the surface morphology of multicomponent polymer systems, techniques are needed that provide two distinct types of information, namely spatial resolution on various length scales within the surface layer and sufficient depth resolution so that one can observe the transition from surface to bulk structure in the material. When the domain sizes are on the order of micrometres, they should be visible by optical microscopy. 

Multicomponent organic polymer materials such as polymer blends are important in industry. Their macroscopic properties are determined not only by the molecular properties of the individual polymers, but also by the miscibiUly, morphology and structure of the interfaces between the polymers. Solid state NMR is a useful tool to study the microscopic struc ture of heterogeneous polymer materials. 

The physical properties of multicomponent polymeric materials are determined to a great extent by their phase behavior. For polymer systems forming separate phases, important issues are phase morphology, i.e. size, shape, and connectivity, and the nature of the interfacial adhesion between the phases. These features of morphology are key issues in the formation of microporous structures in membranes, hollow fibers, and may also be used for preparation of high-impact, high toughness composites. 

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