Application of SAS to Bulk Amorphous Polymers, Block Copolymers and Polymer Blends
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APPLICATION OF SAS TO BULK AMORPHOUS POLYMERS, BLOCK COPOLYMERS AND POLYMER BLENDS R. J. ROE Department of Materials Science and Engineering, Cincinnati, OH 45221-0012
University of Cincinnati,
ABSTRACT. This article discusses the application of small-angle neutron and X-ray scattering techniques to the study of bulk amorphous polymers, block copolymers and polymer blends. The subject matter discussed include density fluctuation in single component amorphous polymers, concentration fluctuation in compatible polymer blends and its interpretation in terms of the random phase approximation theory, analysis of the scattering from incompatible polymer blends as developed by Porod, determination of the phase boundary thickness, order-disorder transition in block copolymer, interpretation of the scattering from disordered block copolymer systems by means of the random phase approximation theory, characterization of ordered block copolymer structure, and the study of block copolymer micelles. INTRODUCTION. In this fourth part of the lecture series on "Introduction to Small-Angle Scattering," the application of small-angle neutron and X-ray scattering methods to the study of bulk amorphous polymers, block copolymers and polymer blends will be discussed. The scattering from amorphous polymers in the small-angle region always includes the contribution from the density fluctuation present in all liquids and amorphous polymers both above and below T . From compatible polymer blends additional scattering arises from the plesence of concentration fluctuation, which can be interpreted in terms of the Ornstein-Zernike formalism or the random phase approximation theory. In the case of incompatible blends, the small-angle scattering provides information on the size and relative amounts of the two phases and the thickness of the diffuse interface between the phases. With block copolymers, either alone or in blends with other polymers, the scattering method can be utilized to study the order-disorder transition. In the disordered phase above the transition temperature, the scattering intensity can be analyzed in terms of the random phase approximation theory, while the data from the ordered phase can provide information on the macrolattice and microdomains. The micelles, which are formed by a small amount of block copolymer added to either a homopolymer or a solvent, can be studied by means of SAS for the characterization of the critical micelle concentration and their size and other structural parameters. DENSITY FLUCTUATION IN BULK AMORPHOUS POLYMERS. Pure amorphous materials, whether ordinary liquids, rubbery polymers or glassy polymers, all possess some degree of spatial inhomogeneity in their density. In the case of liquids and rubbery polymers, the inhomogeneity changes rapidly with time as a result of thermal motion of atoms and molecules, while in the case of the glassy polymers the inhomogeneity is largely frozen-in. Scattering of neutrons and X-rays arises from the presence of such spatial density fluctuations, irrespective
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