Abstract
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.
Highlights
Optical spectroscopy has been used extensively to characterise polymeric and macromolecular materials [1]
Fourier-transform Infrared (FTIR) and Raman spectroscopy have been the most versatile methods to identify specific structural features related to polymer conformation in the solid and molten phases
We have recently demonstrated how broadband, high-resolution inelastic neutron scattering (INS), as that afforded by the TOSCA spectrometer at the ISIS Facility (United Kingdom) [8], constitutes an exquisite characterisation tool to study soft hydrogenous matter confined in graphite-oxide (GO) materials [9, 10, 11]
Summary
Optical spectroscopy has been used extensively to characterise polymeric and macromolecular materials [1]. Both the interlayer spacing and the amount of EG and nPEO do not depend strongly on intercalate chain length, a strong indication that the oligomer and polymer chains are forced to adopt a planar conformation in a monolayer arrangement, i.e., well-defined and extreme two-dimensional (2D) confinement.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
