title: Dynamic Odd-Even Effect in Liquid n-Alkanes near Their Melting Points.
abstract: n-Alkanes are the textbook examples of the odd-even effect: The difference in the periodic packing of odd- and even-numbered n-alkane solids results in odd-even variation of their melting points. However, in the liquid state, in which this packing difference is not obvious, it seems natural to assume that the odd-even effect does not exist, as supported by the monotonic dependence of the boiling points of n-alkanes on the chain length. Herein, we report a surprising odd-even effect in the translational diffusional dynamic properties of n-alkanes in their liquid states. To measure the dynamics of the molecules, we performed quasi-elastic neutron scattering measurements near their melting points. We found that odd-numbered n-alkanes exhibit up to 30 times slower dynamics than even-numbered n-alkanes near their respective melting points. Our results suggest that, although n-alkanes are the simplest hydrocarbons, their dynamic properties are extremely sensitive to the number of carbon atoms.
authors.affiliation: Department of Materials Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Yang
authors.affiliation: Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
authors.forename: Zhikun
authors.initials: Z
authors.lastname: Cai
authors.affiliation: Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Jaiswal
authors.affiliation: NIST Center for Neutron Research, National Institute for Standards and Technology, Gaithersburg, MD, 20899, USA.|Department of Materials Science and Engineering, University of Maryland, College Park, MD, 20742, USA.
authors.forename: Madhusudan
authors.initials: M
authors.lastname: Tyagi
authors.affiliation: Department of Chemistry, Department of Materials Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Moore
authors.affiliation: Department of Nuclear, Plasma, and Radiological Engineering, Department of Materials Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA. zhyang@illinois.edu.
authors.forename: Yang
authors.identifier: 0000-0002-7339-8342
authors.initials: Y
authors.lastname: Zhang
keywords: alkanes; molecular dynamics; odd-even effect; quasi-elastic neutron scattering; relaxation times