1,721,009 research outputs found
Simulazioni mesoscopiche della dinamica di polimeri nei fusi e nelle soluzioni concentrate
No full textPrimitive chain network simulations of conformational relaxation for individual molecules in the entangled state
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METHOD FOR ANALYZING MOLECULAR MOTION OF BRANCHED LONG CHAIN POLYMER
No full textA method for analyzing molecular motion of a branched long chain polymer wherein the position coordinate, the orientation vector, the number of monomers in the constituent elements of a tube and counterpart tube constituent elements forming entanglement are time-developed over a unit time defined by expression 7 according to the Langevin equation defined by expression 1 on the basis of the reptation theory with regard to an inter-tube constituent element constituting each polymer produced by coarse-graining the polymers of a mixture of the branched long chain polymer material to be analyzed according to the entanglement molecular weight (step 201), the number of monomers in the constituent element of the tube is time-development according to expression 5 (step 202), the number n of monomers in the constituent element of the tube at each end of a polymer is monitored, the constituent element of the counterpart tube forming entanglement is altered according to expression 8, and geometrical position exchange is caused to take place between the entanglement and a branch point by the number of constituent element of the tube at a branch part belonging to the branch poin
Primitive chain network model for block copolymers
No full textA coarse-grained molecular simulation for block copolymers in the entangled state is proposed as an extension of the primitive chain network model. Polymers are represented as a sequence of segments between consecutive entanglements, the latter being modeled as sliplinks with other chains. Each sliplink connects two chains only, i.e., entanglements are taken as ‘binary’. The resulting 3D structure is a network of primitive chains, which makes our model different from other sliplink single-chain models, where the link to other chains is ‘virtual’. The 3D nature of our simulation makes it similar to, though considerably more coarse grained than, conventional molecular dynamics simulations. Because of the 3D space assignment of the polymers, monomeric density fields can be defined, and interactions due to different chemistry of the monomers can be accounted for, similarly to density field calculations. Polymer motion is described both by the 3D motion of sliplinks, and by the 1D transport of monomers along the primitive chain, while network topological rearrangement occurs due to chain-end hooking and unhooking processes. Each kinetic equation accounts for elastic forces along the chains, field forces arising from density gradients, and thermal random forces. In this paper, the primitive chain network model was modified (i) in the procedure of network rearrangement to account for the different chemistries in the copolymer, and (ii) in some details of the kinetic equations whenever the boundary between blocks is involved. We report results for diblock copolymers where for simplicity all relevant properties of the two monomers are the same, except for the interactions. Simulations reasonably reproduce the micro-phase formation process and the phase diagram for well entangled copolymers with a low calculation cost
Wall slip in primitive chain network simulations of shear startup of entangled polymers and its effect on the shear stress undershoot
No full textIn some recent experiments on entangled polymers of stress growth in the startup of fast shear flows, an undershoot in the shear stress is observed following the overshoot, i.e., before approaching the steady state. Whereas tumbling of the entangled chain was proposed to be at its origin, here, we investigate another possible cause for the stress undershoot, i.e., slippage at the interface between the polymer and solid wall. To this end, we extend the primitive chain network model to include slip at the interface between entangled polymeric liquids and solid walls with grafted polymers. We determine the slip velocity at the wall, and the shear rate in the bulk, by imposing that the shear stress in the bulk polymers is equal to that resulting from the polymers grafted at the wall. After confirming that the predicted results for the steady state are reasonable, we examine the transient behavior. The simulations confirm that slippage weakens the magnitude of the stress overshoot, as reported earlier. The undershoot is also weakened, or even disappears, because of a reduced coherence in molecular tumbling. Disentanglement of grafted chains from bulk ones, taking place throughout the stress overshoot region, does not contribute to the stress undershoot
METHOD AND PROGRAM FOR ANALYZING MOLECULAR MOTION OF POLYMER COMPOUND
No full textA method for analyzing the molecular motion of a polymer compound which comprises forming, according to the reptation theory, tube−constituting elements composing each polymer molecule through a macroscopic operation based on an entanglement molecular weight with respect to the polymer molecule of the polymer compound, subjecting the position coordinates and orientation vectors of the tube−constituting elements, the numbers of monomers in the tube−constituting elements, and the tube−constituting elements playing opposite at the formation of entanglement, to time development according to Langevin equation over the unit time defined by the formula (4) (step 201), subjecting the numbers of monomers in the tube−constituting elements to time development according to equation (2) (step 202), monitoring the number (n) of monomers in the tube−constituting element positioning in each terminal of the polymer molecule, and changing the tube−constituting elements playing opposite at the formation of entanglement according to the formula (5)
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