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Research Highlight

Mass Loss Revealed as the Origin of Densification in Polyzwitterion Thin Films Under Electric Fields via Neutron and X-ray Reflectometries

Mass Loss Revealed as the Origin of Densification in Polyzwitterion Thin Films Under Electric Fields via Neutron and X-ray Reflectometries
(a) Effects of added deuterated salt (EMIMBF4-d11) on NR from a thin film containing PZ-poly(1-(3-sulfopropyl-1)-2-vinylpyridinium betaine) blends. (b) Neutron scattering length density (NSLD) for best fits of NR data shown in (a). (c) XRR from the same film at room temperature. (d) Locally varying total mass density inside the film at different conditions. An increase in the temperature and the applied electric field leads to shrinkage of the film.

Scientific Achievement

In situ neutron reflectometry (NR) in the presence of applied voltages and a posteriori X-ray reflectometry (XRR) revealed that structural changes within the films containing polyzwitterions (PZs) resulted from the capture of water from the ambient environment and its subsequent loss on heating and did not result from electrostrictive effects, i.e., densification due to non-uniform electric fields.

Significance and Impact

This work shows that solid films containing PZs are extremely hygroscopic and care must be taken when interpreting their responses to applied electric fields especially if they are exposed to ambient environment even for a few seconds.

Research Details

  • The responses of four ultrathin films containing PZ-salt blends to applied electric fields were measured using in situ NR at room temperature and 150oC.
  • In contrast to expected large electrostrictive effects in films containing PZs, changes in the NR and subsequent XRR resulted from the loss of water and its capture, respectively, from the ambient environment

 

Christakopoulos et al., ACS Applied Materials & Interfaces 16 (36), 48307-48319 (2024). DOI: 10.1021/acsami.4c09938

Work conducted at the Center for Nanophase Materials Sciences and the Spallation Neutron Source.