Confinement-induced miscibility in polymer blends

Abstract

The use of polymer thin films in technology is increasingly widespread—for example, as protective or lithographic surface coatings, or as active (electronic or optical) elements in device architectures. But it is difficult to generate films of polymer mixtures with homogeneous surface properties, because of the tendency of the polymers to phase-separate1,2. Copolymer compatibilizers can induce miscibility in polymer blends, but only with chemical components that are either close to a critical point in the phase diagram3 or which have an attractive interaction between them4,5. Instead of manipulating the chemical composition of the blend, we show here that complete mixing can be obtained in polymer blends by the physical effect of confinement in thin films. The compatibilization results from entropic inhibition of phase separation into micelles, owing to confinement. The result is an intimately mixed microemulsion with a perfectly flat surface and a two-dimensional maze-like structure with columnar domains that extend through the film.

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Figure 1: Results of the SCF calculations showing the effect of confinement on micelle formation.
Figure 2: SFM topographical images of bilayer samples.
Figure 3: NEXAFS microscopy images showing the effect of the PS film thickness on morphology after annealing.
Figure 4: SFM images showing the location of diblocks at the interface between the two homopolymers.

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Acknowledgements

NEXAFS microscopy was performed with the Stony Brook STXM at the National Synchrotron Light Source, developed by the groups of J. Kirz and C. Jacobsen with support from the Office of Biological and Environmental Research, and the NSF. We thank S. Spector and C. Jacobsen for developing the zone plates, with support from the NSF. The NSLS is supported by the Office of Basic Energy Sciences, Energy Research, Department of Energy. This work was supported by the NSF DMR-MRSEC Program and by a NSF Young Investigator award.

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Correspondence to D. Gersappe.

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