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Sequential vapor doping is a vital process in controlling the electronic transport properties of semiconducting polymers relevant to opto-electronic and thermoelectric applications. Here, we employed an in situ conductivity method to determine the temporal electronic conductivity ( σ ) profile when vapor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) doping poly(3-hexylthiophene) (P3HT) thin films held at a different temperatures. The temporal profile of σ first showed a fast exponential increase, followed by a brief linear increase until reaching a σ max , and followed by a slow decay in σ . The σ profile were correlated to structural changes through a combination UV-vis-NIR spectroscopy, X-ray scattering, and Raman spectroscopy. We find that the timing for σ max , and subsequent drop in σ of P3HT:F4TCNQ thin films corresponds to the evolution of doping in the crystalline (ordered) and amorphous (disordered) domains. Specifically, Raman spectroscopy resonant at 785 nm highlighted that the crystalline domains reached their saturated doping level near σ max and subsequent smaller level of doping occurred in regions in the disordered domains. Overall, this study emphasizes the importance of granular understanding of σ and the corresponding structural changes in the crystalline and amorphous domains.
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This content will become publicly available on January 17, 2026
Confocal Raman Microscopy for Measuring In Situ Temperature-Dependent Structural Changes in Poly(Ethylene Oxide) Thin Films
Crystallization from the melt is a critical process governing the properties of semi-crystalline polymeric materials. While structural analyses of melting and crystallization transitions in bulk polymers have been widely reported, in contrast, those in thin polymer films on solid supports have been underexplored. Herein, in situ Raman microscopy and self-modeling curve resolution (SMCR) analysis are applied to investigate the temperature-dependent structural changes in poly(ethylene oxide) (PEO) films during melting and crystallization phase transitions. By resolving complex overlapping sets of spectra, SMCR analysis reveals that the thermal transitions of 50 µm thick PEO films comprise two structural phases: an ordered crystalline phase and a disordered amorphous phase. The ordered structure of the crystalline PEO film entirely disappears as the polymer is heated; conversely, the disordered structure of the amorphous PEO film reverts to the ordered structure as the polymer is cooled. Broadening of the Raman bands was observed in PEO films above the melting temperature (67 °C), while sharpening of bands was observed below the crystallization temperature (45 °C). The temperatures at which these spectral changes occurred were in good agreement with differential scanning calorimetry (DSC) measurements, especially during the melting transition. The results illustrate that in situ Raman microscopy coupled with SMCR analysis is a powerful approach for unraveling complex structural changes in thin polymer films during melting and crystallization processes. Furthermore, we show that confocal Raman microscopy opens opportunities to apply the methodology to interrogate the structural features of PEO or other surface-supported polymer films as thin as 2 µm, a thickness regime beyond the reach of conventional thermal analysis techniques.
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- Award ID(s):
- 1922956
- PAR ID:
- 10566877
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- Applied Spectroscopy
- ISSN:
- 0003-7028
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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