Neutron Spectroscopy as a Probe of Macromolecular Structure and Dynamics under Extreme Spatial Confinement

6th Meeting of the Spanish Neutron Scattering Association

Barroso-Bujans, F.^1 ; Fernandez-Alonso, F.^2,3 ; Colmenero, J.^1,4,5

Centro de Física de Materiales (CSIC-UPV/EHU), Material Physics Center (MPC), Paseo Manuel Lardizábal 5, San-Sebastian

20018, Spain^1

ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, Chilton, Didcot

OX11 0QX, United Kingdom^2

Department of Physics and Astronomy, University College London, Gower Street, London

WC1E 6BT, United Kingdom^3

Departamento de Física de Materiales, Universidad Del País Vasco (UPV/EHU), Aptdo 1072, San-Sebastian

20080, Spain^4

Donostia International Physics Center, Paseo Manuel Lardizábal 4, San-Sebastian

20018, Spain^5

关键词: Chemical compositions;    High resolution neutron spectroscopy;    Interfacial adsorption;    Intermolecular modes;    Macromolecular structures;    Surface immobilization;    Terahertz frequency range;    Two-dimensional confinement;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/549/1/012009/pdf
DOI  :  10.1088/1742-6596/549/1/012009

来源: IOP

【 摘 要 】

We illustrate the use of high-resolution neutron spectroscopy to explore the extreme spatial confinement of soft matter in nanostructured materials. Two well-defined limits are considered, involving either intercalation or interfacial adsorption of the ubiquitous polymer poly(ethylene oxide) in graphite-oxide-based hosts. Vibrational modes associated with the confined macromolecular phase undergo dramatic changes over a broad range of energy transfers, from those associated with intermolecular modes in the Terahertz frequency range (1 THz 33 cm-1), to those characteristic of strong chemical bonds above 2000 cm-1. We also consider the effects of polymer chain size and chemical composition of the host material. Variation of the degree of oxidation and exfoliation of graphite oxide leads to two distinct cases, namely: (i) subnanometer two-dimensional confinement; and (ii) surface immobilization. Case (i) is characterised by significant changes to conformational and collective vibrational modes of the polymer as a consequence of a preferentially planar trans-trans-trans chain conformation, whereas case (ii) leads to a substantial increase in the population of gauche conformers. Macroscopically, case (i) translates into the complete suppression of crystallization and glassy behaviour. In contrast, case (ii) exhibits well-defined glass and melting transitions associated with the confined phase, yet at significantly lower temperatures than those of the bulk.