Dear Anis Aqilah,

I have attached some articles and books which explain every thing in details about viscoelastic behavior of polymers and its dependence on polymer structure and temperature.

I hope they would be useful.

I have attached one article and one book.

I hope they would be useful.

thank you so much Mina Karimi-Avargani

Dear Anis,

the ideal elastic body, such as a diamond crystal or a piece of good steel, when exposed to stress deforms immediately and perfectly reversibly. This is ideal elastic behavior according to the Hook law. In contrast, the Ideal liquid

when exposed to stress deforms also immediately but perfectly irrevesibly- (it flows and the rate of its deformation is expressed by the Newton law.

The ideal viscoelastic body, such as a band of vulcanized rubber that you might use to arrange you hairs, exhibits combination of the elastic body and a viscous body - when exposed to an external stress, it deformes perfectly reversibly but with a delay, because extension of the subchains between knot-points of the rubber network from the coiled to extended conformations takes some time. Reversibility of this deformation stems from the fact that the equilibrium conformations of unloaded subchains are the coiled conformations. Therefore, when outer stress is removed, the body returns to its original shape encoded in the network knot-points and coiled conformations of subchains. If a linear polymer is loaded with stress, it first deforms like a viscoelastic network polymer but then it irreversibly flows. This behavior originates from the length of its molecules. Long molecules do entangle and the formed entanglements acts as the knot points of the physical network. (Vulcanized rubber is the network with chemical knot points). Note, the longer are your hairs the worse in¨s to comb them in the morning. However, when the stress acts for a long time, the physical knot points, which are subject to the permanent thermal vibrations and other local motions, slowly disentangle and make new entanglements, which results in the permanent deformation of the polymer body. (principle of proceesing thermoplastic polymers towards products. These are the brieff half-page principles of viscoelasticity.

Best regards, Jiri

Dear all, I would like to add that the elastic character of a material Comes from its ability to store the energy input from a given stress, and use it to recal back to its original dimensions. Many mechanisms are possible to achieve that.

On the other side the viscous character comes from the inability to store the input energy, which is generally lost After sliding of the molecules/chains past each other, and when the stress is released, there is no possibility to reach back the original dimensions. Hysteresis is the factor which tell how elastic/viscous is the material. My Regards

I suggest flowing papers

https://www.sciencedirect.com/topics/materials-science/viscoelastic-behavior

I'm more involved with thermoplastics. After having read all the relevant contributions stated above , I would just add the importance of the correlation between MWD and molecular weights with G' ( storage modulus) , G" ( loss modulus) and ETA* ( complex viscosity) , Gc ( G', G" cross over ) against w( frequency in rd/s - covering a low frequencies range ) and Wc ( cross over) @ a certain temperature. As already mentioned in previous comments / articles , as molecular entanglement knots increase , as a result of molecular weight increase and broader WWD, melt elasticity also increases reflecting in a shift of the cross over point (Gc, wc) . This can be correlated with some polymer processing issues ( usually associated with the elastic recovery of larger polymer molecules ) and end use performance, in the polymer producing and converting industries . For instance fibers ( due to better spinability) and injection molding ( less warpage in molded part ) tend to benefit from lower molecular weights and narrow MWD whereas thermoforming and blow molding ( due to higher melt strength) tend to benefit from larger molecular weights and broader MWD.