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

Importance of the Topic

Phase separation of polymer blends and the controlled deposition of nanomaterials are critical for developing advanced coatings, sensors and electronic interfaces. Mapping single‐walled carbon nanotubes (SWCNT) on polymer surfaces provides insight into selective adhesion, surface coverage and composite functionality. Raman spectroscopy offers a non‐destructive, chemically specific imaging technique with micron‐scale resolution, ideal for characterizing polymer domains and nanotube distributions.

Study Objectives and Overview

This work aimed to demonstrate dispersive Raman mapping as a tool to: 1) confirm phase separation in vapor‐deposited polystyrene (PS) and polymethylmethacrylate (PMMA) films on silicon, 2) visualize the preferential deposition of SWCNT on PS regions, and 3) quantify surface coverage of both polymers and nanotubes.

Methodology

• Sample Preparation:

• Successive vapor deposition of PS and PMMA onto silicon wafers yielded phase‐separated domains (10–50 μm wide).
• SWCNT were vacuum‐deposited atop the polymer films.

• Raman Mapping:

• Instrument: 532 nm laser, 8 s exposure per point, 1271 collection points.
• Spectral band of interest: 1605 cm⁻¹ C–C stretch characteristic of PS.
• Correlation analysis used SWCNT reference spectrum to identify nanotube‐rich regions.

Used Instrumentation

• Thermo Scientific Nicolet Almega XR dispersive Raman spectrometer configured for 532 nm excitation.
• OMNIC Atlµs software suite for chemical imaging, mapping and correlation analysis.
• Raman microscope with brightfield/darkfield, polarization and DIC enhancements.

Main Results and Discussion

• Chemical Mapping of Polymers:

• Intensity map of the 1605 cm⁻¹ band distinguished PS (red/yellow/green) from PMMA (blue) domains.

• SWCNT Distribution:

• Correlation maps showed preferential SWCNT aggregation on PS regions; red pixels indicated correlation coefficients near 1.0 with the SWCNT reference.
• Quantitative image analysis determined PS coverage of ~38% and SWCNT coverage of ~5% in the mapped area.

• Spectral Features:

• PS domains confirmed by comparison to a PS standard after silicon background subtraction.
• SWCNT signature bands: G band at ~1598 cm⁻¹, D band at ~1327 cm⁻¹, and radial breathing modes at 185–267 cm⁻¹.

Benefits and Practical Applications

• High spatial resolution (<1 μm) enables fine mapping of polymer/nanotube interfaces.
• Non‐destructive analysis on non‐reflective substrates expands applicability beyond IR techniques.
• Quantitative coverage data supports quality control in coatings and composite fabrication.
• Sensitivity to molecular structure allows detection of functionalization or defects in nanotubes.

Future Trends and Applications

• Integration with multivariate analysis (PCA, MCR) for automated component deconvolution.
• Expansion to in situ monitoring of vapor deposition and self‐assembly processes.
• Correlation with electrical or mechanical measurements to link morphology and performance.
• Application to other nanomaterial/polymer systems for sensor, photovoltaic and barrier coatings.

Conclusion

Dispersive Raman mapping on the Almega XR provided a robust approach to distinguish PS and PMMA phases, locate SWCNT deposition sites, and quantify surface coverage. The method demonstrated high chemical specificity, spatial resolution and quantitative imaging capabilities, making it a valuable tool for research and quality control in polymer‐nanotube systems.