Polymer Melt Dynamics By Nmr Relaxation Measurements

Polymers exhibit a range of physical characteristics, from rubber-like elasticity to the glassy state. These particular properties are controlled at the molecular level by the mobility of the structural constituents. Remarkable changes in mobility can be witnessed with temperature, over narrow, well defined regions, termed relaxation processes. This is an important, unique phenomenon controlling polymer transition behaviour and is described here at an introductory level. The important types of relaxation processes from amorphous to crystalline polymers and polymeric miscible blends are covered, in conjunction with the broad spectrum of experimental methods used to study them. In-depth discussion of molecular level interpretation, including atomistic level computer simulations and applications to molecular mechanism elucidation, are discussed. The result is a self-contained approach to polymeric interpretation suitable for researchers in materials science, physics and chemistry interested in the relaxation processes of polymeric systems.

Field-cycling NMR relaxometry is evolving into a methodology of widespread interest with recent technological developments resulting in powerful and versatile commercial instruments. Polymers, liquid crystals, biomaterials, porous media, tissue, cement and many other materials of practical importance can be studied using this technique. This book summarises the expertise of leading scientists in the area and the editor is well placed, after four decades of working in this field, to ensure a broad ranging and high quality title. Starting with an overview of the basic principles of the technique and the scope of its use, the content then develops to look at theory, instrumentation, practical limitations and applications in different systems. Newcomers to the field will find this book invaluable for successful use of the technique. Researchers already in academic and industrial settings, interested in molecular dynamics and magnetic resonance, will discover an important addition to the literature.

Cover -- Contents -- Preface -- PART I: MOLECULAR DYNAMICS -- Chapter I.1. The reptation model : tests through diffusion measurements in linear polymer melts -- Introduction -- The reptation model -- Diffusion measurements in polymer systems -- Interpretation and comparison with rheometrical data -- Conclusions -- Chapter I.2. Polybutadiene : NMR and Temporary elasticity -- Introduction -- Temporary network structures -- Segmental motions : dynamic screening effect -- Molten high polymers : semi-local dynamics -- Conclusion -- Chapter I.3. Chain relaxation processes of uniaxially stretched polymer chains : an infrared dichroism study -- Introduction -- Theoretical background in Infrared dichroism -- Experimental -- Theoretical basis of interpretation -- Results and discussion on isotopically labeled chains -- Results and discussion on isotopically labelled 6-arm stars -- Results and discussion on binary blends of long and short chains -- Conclusion -- Chapter I.4. Chain conformation in ...

This series presents critical reviews of the present and future trends in polymer and biopolymer science including chemistry, physical chemistry, physics and materials science. It is addressed to all scientists at universities and in industry who wish to keep abreast of advances in the topics covered. Impact Factor Ranking: Always number one in Polymer Science. More information as well as the electronic version of the whole content available at: www.springerlink.com

New physics emerges when polyphenylmethylsiloxane (PPMS) adsorbed between mica surfaces spaced at molecular dimensions undergoes oscillatory shear. The polymers experience a dynamic liquid-like to rubber-like transition at the onset of long range surface forces $(sim$4.5 R$sb{rm G}).$ The long time relaxations of the polymers are effectively frustrated at the start of the strong repulsive short range surface forces (hard-wall $sim$2.8 R$sb{rm G}).$ The static surface forces and dynamic regimes scale with the size of the polymer molecules. This reflects the universal ranges of polymer melts perturbed by the adsorbing surfaces. The dynamics manifest a nonequilibrium freezing of certain degrees of freedom of the molecules as the film thickness decreases. In the rubber-like regime (2.8-4.5 R$sb{rm G}),$ the linear relaxation modulus resembles that of an entangled polymer melt. Surprisingly, the molecular weights of the PPMS are less than the entanglement molecular weight. The dynamics are not reptation in nature; they reflect the long range topological constraints imposed by the adsorbing surfaces. In the short range hard-wall regime $(