RT info:eu-repo/semantics/article
T1 Molecular Dynamics Test of the Stress-Thermal Rule in Polyethylene and Polystyrene Entangled Melts
A1 Nieto Simavilla, David
A1 Sgouros, Aristotelis P.
A1 Vogiatzis, Georgios G.
A1 Tzoumanekas, Christos
A1 Georgilas, Vasilis
A1 Verbeeten, Wilco M.H.
A1 Theodorou, Doros N.
K1 Stress
K1 Thermal conductivity
K1 Deformation
K1 Magnetic properties Polyethylene
K1 Materiales
K1 Materials
AB Anisotropic thermal transport induced by deformationand the linear relation between the thermal conductivity andstress tensors, also known as the stress-thermal rule (STR), aretested via molecular dynamics simulations in well-entangled linearpolyethylene (PE) and polystyrene (PS) melts subjected toextensional flow. We propose a method to determine the stressin deformed molecular melts, a key component missing in priorsimulation studies on thermal transport in polymers that preventedverification of the STR. We compare our results with available datafrom previous experimental and simulation studies. Thermalconductivity (TC) is found to increase (decrease) in the directionparallel (perpendicular) to the imposed stretch. We find that the STR is valid for both PE and PS over a wide range of deformationrates and stress levels. In direct agreement with experimental evidence and the STR, we observe that for a given strain, the anisotropyin TC increases with the strain rate. Surprisingly, our results for PE question the universal behavior with respect to polymerchemistry suggested by experiments by showing a significantly higher proportionality constant (the stress-thermal coefficient)between stress and anisotropy in TC. We argue that this discrepancy can be explained by the high degree of entanglementinteractions in PE affecting the transport of energy at the molecular level. Our conjecture is tested by studying an entangled linear PSmelt, a polymer with a much lower entanglement plateau, for which thermal transport experimental results are available. For PS, thenormalized stress-thermal coefficient is found to be commensurate with the experimental value. Finally, we test the fundamentalmolecular hypothesis of preferential energy transport along the backbone of polymer chains used to formulate the STR, which wasprompted by early experimental evidence showing an increase in TC with chain length. We are able to establish that the increase inTC with chain length in PE melts fades as the system becomes entangled (i.e., TC remains constant beyond the criticalentanglement chain length that marks the transition to entanglement-dominated rheological behavior). Our findings are of keyimportance in developing robust molecular-to-continuum methodologies for the study of nonisothermal macroscopic flows that areextremely relevant to polymer manufacturing processes.
PB American Chemical Society
YR 2020
FD 2020-02
LK http://hdl.handle.net/10259/5254
UL http://hdl.handle.net/10259/5254
LA eng
NO European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie IF MTCIATTP 750985.
DS Repositorio Institucional de la Universidad de Burgos
RD 24-abr-2024