title: Study of liquid-phase molecular packing interactions and morphology of fatty acid methyl esters (biodiesel).
abstract: BACKGROUND
  (1)H low field nuclear magnetic resonance (LF-NMR) relaxometry has been suggested as a tool to distinguish between different molecular ensembles in complex systems with differential segmental or whole molecular motion and/or different morphologies. In biodiesel applications the molecular structure versus liquid-phase packing morphologies of fatty acid methyl esters (FAMEs) influences physico-chemical characteristics of the fuel, including flow properties, operability during cold weather, blending, and more. Still, their liquid morphological structures have scarcely been studied. It was therefore the objective of this work to explore the potential of this technology for characterizing the molecular organization of FAMEs in the liquid phase. This was accomplished by using a combination of supporting advanced technologies.
  
  
  RESULTS
  We show that pure oleic acid (OA) and methyl oleate (MO) standards exhibited both similarities and differences in the (1)H LF-NMR relaxation times (T2s) and peak areas, for a range of temperatures. Based on X-ray measurements, both molecules were found to possess a liquid crystal-like order, although a larger fluidity was found for MO, because as the temperature is increased, MO molecules separate both longitudinally and transversely from one another. In addition, both molecules exhibited a preferred direction of diffusion based on the apparent hydrodynamic radius. The close molecular packing arrangement and interactions were found to affect the translational and segmental motions of the molecules, as a result of dimerization of the head group in OA as opposed to weaker polar interactions in MO.
  
  
  CONCLUSIONS
  A comprehensive model for the liquid crystal-like arrangement of FAMEs in the liquid phase is suggested. The differences in translational and segmental motions of the molecules were rationalized by the differences in the (1)H LF-NMR T2 distributions of OA and MO, which was further supported by (13)C high field (HF)-NMR spectra and (1)H HF-NMR relaxation. The proposed assignment allows for material characterization based on parameters that contribute to properties in applications such as biodiesel fuels.
authors: The Phyto-Lipid Biotechnology Laboratory, Departments of Biotechnology, Energy and Environmental Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
authors: Paula
authors: P
authors: Berman
authors: The Phyto-Lipid Biotechnology Laboratory, Departments of Biotechnology, Energy and Environmental Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
authors: Nitzan
authors: N
authors: Meiri
authors: Embrapa Instrumentação, Rua 15 de Novembro 1452, São Carlos, SP 13560-970 Brazil.
authors: Luiz Alberto
authors: LA
authors: Colnago
authors: Instituto de Física de São Carlos, Universidade de São Paulo, Av. Trabalhador Sao-Carlense 400, São Carlos, SP 13566-590 Brazil.
authors: Tiago Bueno
authors: TB
authors: Moraes
authors: Zuckerberg Center for Water Sciences and Technology and Department of Biotechnology, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
authors: Charles
authors: C
authors: Linder
authors: Department of Industrial Engineering and Management, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
authors: Ofer
authors: O
authors: Levi
authors: Department of Industrial Engineering and Management, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
authors: Yisrael
authors: Y
authors: Parmet
authors: Department of Management Science and Engineering, Stanford University, Stanford, CA USA.
authors: Michael
authors: M
authors: Saunders
authors: The Phyto-Lipid Biotechnology Laboratory, Departments of Biotechnology, Energy and Environmental Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel.
authors: Zeev
authors: Z
authors: Wiesman
keywords: 1H low field nuclear magnetic resonance relaxometry; Biodiesel physical properties; Methyl oleate; Molecular packing; Oleic acid; Segmental motion