Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

An interfacial instability in a transient wetting layer leads to lateral phase separation in thin spin-cast polymer-blend films

Abstract

Spin-coating is a very widely used technique for making uniform thin polymer films. For example, the active layers in most experimental semiconducting polymer-based devices, such as light-emitting diodes and photovoltaics, are made this way. The efficiency of such devices can be improved by using blends of polymers; these phase separate during the spin-coating process, creating the complex morphology that leads to performance improvements. We have used time-resolved small-angle light scattering and light reflectivity during the spin-coating process to study the development of structure directly. Our results provide evidence that a blend of two polymers first undergoes vertical stratification; the interface between the stratified layers then becomes unstable, leading to the final phase-separated thin film. This has given us the basis for establishing a full mechanistic understanding of the development of morphology in thin mixed polymer films, allowing a route to the rational design of processing conditions so as to achieve desirable morphologies by self-assembly.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Specular reflectivity measured during the spin-coating process.
Figure 2: Film thickness as a function of time.
Figure 3: A contour plot showing the radially averaged light-scattering intensity out of the specular direction for the blend film.
Figure 4: Fringe visibility for PMMA and PS:PMMA with corresponding models.
Figure 5: Models of PMMA and PS:PMMA.
Figure 6: A schematic model describing the film formation during the spin-coating process, and the final film morphology.

Similar content being viewed by others

References

  1. Geoghegan, M. et al. Lamellar structure in a thin polymer blend film. Polymer 35, 2019–2027 (1994).

    Article  Google Scholar 

  2. Geoghegan, M. & Krausch, G. Wetting at polymer surfaces and interfaces. Prog. Polym. Sci. 28, 261–302 (2003).

    Article  Google Scholar 

  3. Prosycevas, I., Tamulevicius, S. & Guobiene, A. The surface properties of PS/PMMA blends nanostructured polymeric layers. Thin Solid Films 453, 304–311 (2004).

    Article  Google Scholar 

  4. Dekeyser, C. M., Biltresse, S., Marchand-Brynaert, J., Rouxhet, P. G. & Dupont-Gillain, C. C. Submicrometer-scale heterogeneous surfaces by PS-PMMA demixing. Polymer 45, 2211–2219 (2004).

    Article  Google Scholar 

  5. Li, X., Han, Y. C. & An, L. J. Surface morphology control of immiscible polymer-blend thin films. Polymer 44, 8155–8165 (2003).

    Article  Google Scholar 

  6. Raczkowska, J. et al. Surface patterns in solvent-cast polymer blend films analyzed with an integral-geometry approach. Macromolecules 36, 2419–2427 (2003).

    Article  Google Scholar 

  7. Ton-That, C., Shard, A. G. & Bradley, R. H. Surface feature size of spin cast PS/PMMA blends. Polymer 43, 4973–4977 (2002).

    Article  Google Scholar 

  8. Muller-Buschbaum, P., Gutmann, J. S. & Stamm, M. Control of surface morphology by the interplay between phase separation and dewetting. J. Macromol. Sci.-Phys. B 38, 577–592 (1999).

    Article  Google Scholar 

  9. Ade, H. et al. Phase segregation in polymer thin films: Elucidations by X-ray and scanning force microscopy. Europhys. Lett. 45, 526–532 (1999).

    Article  Google Scholar 

  10. DalnokiVeress, K., Forrest, J. A., Stevens, J. R. & Dutcher, J. R. Physica A 239, 87–94 (1997).

    Article  Google Scholar 

  11. Halls, J. J. M. et al. Efficient photodiodes from interpenetrating polymer networks. Nature 376, 498–500 (1995).

    Article  Google Scholar 

  12. Peumans, P., Uchida, S. & Forrest, S. R. Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films. Nature 425, 158–162 (2003).

    Article  Google Scholar 

  13. Morteani, A. C. et al. Barrier-free electron-hole capture in polymer blend heterojunction light-emitting diodes. Adv. Mater. 15, 1708–1712 (2003).

    Article  Google Scholar 

  14. Snaith, H. J. & Friend, R. H. Morphological dependence of charge generation and transport in blended polyfluorene photovoltaic devices. Thin Solid Films 451, 567–571 (2004).

    Article  Google Scholar 

  15. Moons, E. Conjugated polymer blends: linking film morphology to performance of light emitting diodes and photodiodes. J. Phys. C 14, 12235–12260 (2002).

    Google Scholar 

  16. Granstrom, M. et al. Laminated fabrication of polymeric photovoltaic diodes. Nature 395, 257–260 (1998).

    Article  Google Scholar 

  17. Kim, J. S., Ho, P. K. H., Murphy, C. E. & Friend, R. H. Phase separation in polyfluorene-based conjugated polymer blends: Lateral and vertical analysis of blend spin-cast thin films. Macromolecules 37, 2861–2871 (2004).

    Article  Google Scholar 

  18. Chappell, J. et al. Correlating structure with fluorescence emission in phase-separated conjugated-polymer blends. Nature Mater. 2, 616–621 (2003).

    Article  Google Scholar 

  19. Corcoran, N., Arias, A. C., Kim, J. S., MacKenzie, J. D. & Friend, R. H. Increased efficiency in vertically segregated thin-film conjugated polymer blends for light-emitting diodes. Appl. Phys. Lett. 82, 299–301 (2003).

    Article  Google Scholar 

  20. Arias, A. C. et al. Vertically segregated polymer-blend photovoltaic thin-film structures through surface-mediated solution processing. Appl. Phys. Lett. 80, 1695–1697 (2002).

    Article  Google Scholar 

  21. Boltau, M., Walheim, S., Mlynek, J., Krausch, G. & Steiner, U. Surface-induced structure formation of polymer blends on patterned substrates. Nature 391, 877–879 (1998).

    Article  Google Scholar 

  22. Walheim, S., Boltau, M., Mlynek, J., Krausch, G. & Steiner, U. Structure formation via polymer demixing in spin-cast films. Macromolecules 30, 4995–5003 (1997).

    Article  Google Scholar 

  23. Jukes, P. C., Heriot, S. Y., Sharp, J. S. & Jones, R. A. L. Time-resolved light scattering studies of phase separation in thin film semiconducting polymer blends during spin-coating. Macromolecules 38, 2030–2032 (2005).

    Article  Google Scholar 

  24. Cahn, J. W. Phase separation by spinodal decomposition in isotropic systems. J. Chem. Phys. 42, 93–99 (1965).

    Article  Google Scholar 

  25. Sferrazza, M. et al. Interfacial instability driven by dispersive forces: The early stages of spinodal dewetting of a thin polymer film on a polymer substrate. Phys. Rev. Lett. 81, 5173–5176 (1998).

    Article  Google Scholar 

  26. Reiter, G. Dewetting of thin polymer-films. Phys. Rev. Lett. 68, 75–78 (1992).

    Article  Google Scholar 

  27. Nevot, L. & Croce, P. Caractérisation des surfaces par réflexion rasant de rayons x: application á l’étude du polissage de quelques verres silicates. Rev. Phys. Appl. 15, 761–779 (1980).

    Article  Google Scholar 

  28. Brochard-Wyart, F., Martin, P. & Redon, C. Liquid/liquid dewetting. Langmuir 9, 3682–3690 (1993).

    Article  Google Scholar 

  29. de Gennes, P. G. Instabilities during the evaporation of a film: Non-glassy polymer plus volatile solvent. Eur. Phys. J. E 6, 421–424 (2001).

    Article  Google Scholar 

  30. Broseta, D., Leibler, L., Kaddour, L. O. & Strazielle, C. A theoretical and experimental study of interfacial-tension of immiscible polymer blends in solution. J. Chem. Phys. 87, 7248–7256 (1987).

    Article  Google Scholar 

  31. Bernasik, A. et al. Lamellar structures formed in spin-cast blends of insulating and conducting polymers. Synth. Met. 144, 253–257 (2004).

    Article  Google Scholar 

  32. Routh, A. F. & Russel, W. B. A process model for latex film formation: Limiting regimes for individual driving forces. Langmuir 15, 7762–7773 (1999).

    Article  Google Scholar 

Download references

Acknowledgements

We would like to thank S. Martin and M. Geoghegan for helpful discussions and EPSRC for financial support.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Sasha Y. Heriot.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary figures S1-S7 (PDF 469 kb)

Supplementary Movie

Supplementary movie S2 (AVI 1544 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Heriot, S., Jones, R. An interfacial instability in a transient wetting layer leads to lateral phase separation in thin spin-cast polymer-blend films. Nature Mater 4, 782–786 (2005). https://doi.org/10.1038/nmat1476

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat1476

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing