Raman Mapping of Single-walled Carbon Nanotube Distribution on Phase Separated Polystyrene and Polymethylmethacrylate

Significance of the Topic

Mapping the distribution of polymers and nanomaterials at the micron scale is critical in optimizing advanced coatings, composite interfaces and electronic devices. Raman imaging provides a non‐destructive approach to visualize phase separation in polymer blends and to locate carbon nanotubes with high spatial resolution, enabling precise material characterization in research and quality control contexts.

Objectives and Study Overview

This study aimed to demonstrate the use of dispersive Raman mapping to:

• Confirm phase separation of vapor-deposited polystyrene (PS) and polymethylmethacrylate (PMMA) on silicon substrates.
• Determine the preferential deposition and coverage of single-walled carbon nanotubes (SWCNTs) on the PS/PMMA patterned surface.

Methodology and Instrumentation

The analysis employed the Thermo Scientific Nicolet Almega XR dispersive Raman spectrometer configured with a 532 nm laser and research-grade microscope. Spectral maps were collected using the OMNIC™ Atlµs™ software, with point exposures of 8 s and step sizes down to 1 µm. Key spectral bands monitored included the 1605 cm−1 PS C–C stretch and characteristic SWCNT features (G band at ~1598 cm−1, D band at ~1327 cm−1 and radial breathing modes at 185–267 cm−1).

Instrumentation Used

• Nicolet Almega XR dispersive Raman spectrometer
• 532 nm visible laser excitation
• OMNIC Atlµs mapping software
• DXR Raman microscope for precise laser power control

Results and Discussion

Chemical imaging of the 1605 cm−1 band revealed PS domains (red/yellow/green) interspersed with PMMA regions (blue). Overlay of chemical and visual images confirmed spatial distribution across 10–50 µm features. Spectral correlation mapping against an SWCNT reference spectrum identified nanotube aggregates primarily on PS, with correlation coefficients approaching unity in red-coded zones. Quantitative image analysis indicated ~38 % surface coverage by PS and ~5 % by SWCNTs within the mapped area.

Benefits and Practical Applications

Dispersive Raman mapping offers:

• Sub-micron spatial resolution for detailed phase morphology studies.
• Non-destructive analysis without reflective substrates.
• Simultaneous chemical and distribution data for polymer blends and nanomaterials.

This method supports material development in coatings, electronics, composites and quality assurance of surface treatments.

Future Trends and Opportunities

Emerging directions include:

1. Integration of multivariate analysis (PCA, MCR) for enhanced component separation.
2. 3D Raman tomography to probe subsurface distributions.
3. Real-time, in situ mapping during film growth or processing.
4. Automated image analysis workflows for high-throughput screening.

Conclusion

Dispersive Raman spectroscopy combined with chemical mapping and image analysis provides a powerful toolkit for characterizing polymer phase separation and carbon nanotube deposition on substrates. The approach yields spatially resolved, quantitative data critical for materials research and industrial applications.