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Mapping the Structure of a Hydrated Polymer Blend Using Energy-Loss Spectroscopy in the Cryo-STEM

Published online by Cambridge University Press:  01 February 2011

Alioscka Sousa ,
Abdelaziz Aitouchen  and
Matthew Libera
Alioscka Sousa
Affiliation:
Department of Chemical, Biomedical, and Materials Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA
Abdelaziz Aitouchen
Affiliation:
FEI Company, Tempe, AZ 85282, USA
Matthew Libera
Affiliation:
Department of Chemical, Biomedical, and Materials Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA
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Abstract

We use electron energy-loss spectroscopy (EELS) in the cryo-STEM to determine the spatial distribution of water in a model frozen-hydrated two-phase polymer blend composed of hydrophilic poly(vinylpyrrolidone) (PVP) and hydrophobic poly(styrene) (PS). We demonstrate that it is possible to directly correlate the water spatial distribution with variations in the underlying polymer morphology. HAADF-STEM imaging of both dry and frozen-hydrated specimens shows weak contrast between the polymer phases but gives no information regarding the composition of these phases and no indication of where water might be localized. Spatially-resolved EELS spectra collected at 100 nm pixel size show that this system is composed of discrete PVP-rich domains dispersed in a continuous PS-rich matrix. The PVP-rich domains were found to be hydrated up to a level of ∼ 23 wt%. We have made our compositional maps fully quantitative, given as mass-fraction maps, by measuring the total inelastic scattering cross-sections per unit mass of water, PVP and PS. This is an important quantity which we have determined for an incident beam energy of 200 keV. Hydrated PVP gives rise to hydrogen evolution when irradiated above an electron dose of 1500 e/nm2 as evidenced from changes in the 13 eV region, and this effect gives rise to dose-limited resolution in these experiments.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 839: Symposium P – Electron Microscopy of Molecular and Atom-Scale Mechanical Behavior, Chemistry, and Structure , 2004 , p6.3
Copyright
Copyright © Materials Research Society 2004

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References

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