Dynamics in the melt

Toomey DR, Wileoek WSD, Conder JA, Forsyth DW, Blundy JD, Parmentier EM, Hanunond WC () Asynunetrie mantle dynamics in the MELT region of the East Pacific Rise. Earth Planet Sci Lett 200 287-295... 

Very simple and fundamental questions are still without answer, and, in the following, we will show how FAD can bring an answer to some of them. For instance one can wonder whether the local dynamics in the melt are affected by chain connectivity at they are in dilute solution, or if the numerous interchain constraints lead to a completely different behavior. Moreover, the relation between molecular motions and macroscopic properties is rather unknown. 

The Rouse limit applies to unentangled polymer melts because hydrodynamic interactions are screened in melts (just as excluded volume interactions are screened in melts). Polymer dynamics in the melt state (with no solvent) are described by the Rouse model, for short chains that are not entangled. 

Siegfried and co-workers (66,67) investigated thermoplastic IPNs based on SEES triblock copolymers with a polystyrene ionomer. Two subclasses of thermoplastic IPNs were identified those prepared by a sequential polymerization method, and those prepared by mechanically blending separately synthesized polymers. In each case, a polystyrene acid sulfate was neutralized dynamically in the melt with a concentrated solution of sodium hydroxide. The water steamed off rapidly under the reaction conditions. The first subclass resulted in lower melt viscosities, but more nearly equal dual-phase continuity was achieved with the second subclass. The subject of thermoplastic IPNs was recently reviewed by Sperling (68). 

An imderstanding of the influence of polydispersity on chain dynamics in the melt was achieved by Baschnagel and co-workers (177) in a simulation using BFM. These dynamic Monte Carlo simulations showed that long chains move more rapidly in the presence of short chains, and the short ones move more slowly in the presence of the long ones. The net effect is that the dsniamics of a polydis-perse melt is close to Rouse theory predictions, ie, the chains act as if they are not entangled An indirect approach to reptation dynamics was described by Byutner... 

Before describing the reptation theory quantitatively, we first examine part of the rich set of behaviors that any theory of polymer chain dynamics in the melt state needs to be able to describe. One of the most interesting aspects of pol5uner melt and solution behavior is that once the material is well entangled, the viscoelastic behavior is quasi-imiversal. First, the zero shear rate viscosity rjo is observed to vary with the molecular weight to a very strong power (9,57) ... 

Viovy JL, Frank CW, Monnerie L (1985) Fluorescence anisotropy decay studies of local polymer dynamics in the melt. 2. Labeled model compounds of variable chain-length. Macromolecules 18(12) 2606-2613. doi 10.1021fina00154a042... 

The aim of this contribution has been to link the basic macroscopic phenomena associated with polymers with the unique features of their structure, the most obvious being the presence of long, flexible molecular chains. The important role of the conformational entropy of flexible chains, not only for rubber elasticity but for polymer dynamics in general, has been demonstrated. Moreover, the concept of an entanglement network, which underpins much of the theory of polymer dynamics in the melt, has also been shown to have important repercussions for the high strain behavior of solid polymers, namely plastic deformation, crazing, and fracture. 

The dynamics in the melt pool result fiom pressure and temperature gradients. Direct effects on the material mixture in the welding seam can be observed. In this way, the influence of welding pressure during quasi-simultaneous welding can be invesli ted. 

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