Negative thermal expansion of poly(vinylidene fluoride) and polyethylene tie molecules: A molecular dynamics study
2016 (English)In: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 54, no 21, p. 2223-2232Article in journal (Refereed) Published
Abstract [en]
The mechanism of thermal actuation for poly(vinylidene fluoride) (PVDF) and polyethylene (PE) tie molecules has been investigated using molecular dynamics simulations. Tie molecules are found in semicrystalline polymers and are polymer chains that link two (or more) crystalline lamellae, allowing for the transfer of force between these regions. A novel simulation technique has been developed to enable measurement of changes in the tie molecule length upon heating. We investigate the dependence of the percentage actuation observed upon heating, on the external applied force that stretches the tie molecules, the temperature range used for heating as well as the length and the number of tie molecules. Two molecular level mechanisms for actuation are identified. An entropically driven mechanism occurs at low applied forces and is applicable to all flexible polymers. A second mechanism due to conformational changes is observed for PVDF but not for PE at intermediate applied forces.
Place, publisher, year, edition, pages
2016. Vol. 54, no 21, p. 2223-2232
Keywords [en]
actuators, molecular dynamics, poly (vinylidene fluoride), polyethylene, simulations and stimuli-sensitive polymers, tie molecules, Fluorine compounds, Molecules, Polyethylenes, Polymers, Thermal expansion, Molecular dynamics simulations, Molecular level mechanisms, Negative thermal expansion, Poly (vinylidene fluoride)(PVDF), Poly(vinylidene fluoride), Semi-crystalline polymer, Stimuli-sensitive polymers
National Category
Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:ri:diva-27591DOI: 10.1002/polb.24131Scopus ID: 2-s2.0-84988019174OAI: oai:DiVA.org:ri-27591DiVA, id: diva2:1057876
2016-12-192016-12-192023-03-27Bibliographically approved