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Unexpected power-law stress relaxation of entangled ring polymers

2008; Nature Portfolio; Volume: 7; Issue: 12 Linguagem: Inglês

10.1038/nmat2292

1476-4660

M. Kapnistos, Michael Lang, Dimitris Vlassopoulos, Wim Pyckhout‐Hintzen, Dieter Richter, Dong Pil Cho, Taihyun Chang, Michael Rubinstein,

Force Microscopy Techniques and Applications

After many years of intense research, most aspects of the motion of entangled polymers have been understood. Long linear and branched polymers have a characteristic entanglement plateau and their stress relaxes by chain reptation or branch retraction, respectively. In both mechanisms, the presence of chain ends is essential. But how do entangled polymers without ends relax their stress? Using properly purified high-molar-mass ring polymers, we demonstrate that these materials exhibit self-similar dynamics, yielding a power-law stress relaxation. However, trace amounts of linear chains at a concentration almost two decades below their overlap cause an enhanced mechanical response. An entanglement plateau is recovered at higher concentrations of linear chains. These results constitute an important step towards solving an outstanding problem of polymer science and are useful for manipulating properties of materials ranging from DNA to polycarbonate. They also provide possible directions for tuning the rheology of entangled polymers. How do entangled polymer rings relax? Linear polymers can ease their stress because their chains have ends, but cyclic polymers do not. Even trace amounts of linear chains dominate the mechanical properties if present as impurities. Investigation of carefully purified ring polymers reveals they exhibit self-similar dynamics and a power-law stress relaxation.