This book describes the solid state behaviour of organic materials based the polymethylene chain, i.e., the functional molecular component of polyethylenes, soaps, detergents, edible fats, lipids, oils, greases, and waxes. Along with chain unsaturation and branching, polydispersity, i.e., the aggregation of several polymethylene chain lengths, is shown to control various physical properties, including the preservation of metastable phases (polymorphic as well as ‘rotator’ forms). Using linear chain waxes as model materials, this book explores how solid solutions are stabilized and what structu ... More

This book describes the solid state behaviour of organic materials based the polymethylene chain, i.e., the functional molecular component of polyethylenes, soaps, detergents, edible fats, lipids, oils, greases, and waxes. Along with chain unsaturation and branching, polydispersity, i.e., the aggregation of several polymethylene chain lengths, is shown to control various physical properties, including the preservation of metastable phases (polymorphic as well as ‘rotator’ forms). Using linear chain waxes as model materials, this book explores how solid solutions are stabilized and what structures are possible. Strictly linear molecules are compared to those functionalized with ‘head-groups’. The onset of fractionation, followed by formation of eutectic phases, is discussed, again describing the structures of favoured molecular assemblies. The rationale for polydisperse aggregation derives from the early work of A. I. Kitaigorodskii, demonstrating how certain homeomorphic parameters such as relative molecular shape and volume, as well as favoured crystalline polymorphs, lead to stable solid solutions. Relevant to high-molecular weight polymers, the influence of chain-folding is also discussed. A comprehensive review of known linear chain single crystal structures, including the alkanes, cycloalkanes, perfluoroalkanes, fatty alcohols, fatty acids, fatty acid esters, and cholesteryl esters, is presented to show how molecular shape, including chain branching, influences layer packing and co-solubility. Finally, a critique of previously suggested models for petroleum and natural wax assemblies is given, based on current crystallographic and spectroscopic information. This includes single crystal structures based on electron diffraction data. Although constrained to single chain molecules in the examples discussed, cited behaviour can be generalized to multiple chain-containing fats and lipids.