X-ray Microscopy and NEXAFS Spectroscopy of Macrophase-Separated Random Block Copolymer/Homopolymer Blends

A. P. Smith, J. H. Laurer, H. W. Ade, S. D. Smith, A. Ashraf and R. J. Spontak

The Problem:
Blends of a homopolymer (polystyrene) and a random block copolymer (RBC) were created to study the phase morphology produced by systems with only very slight incompatabilities.  Although the RBC could be stained and the phase morphology viewed within the TEM, small differences in chemistry were undetectable.  Due to the small incompatabilities of the two polymers, chemical variations within the phases was expected as the two phases mix.  The objective of the x-ray microscopy study was to search for these chemical variations.

The Results:
Below is a TEM image of the blend acquired after the RBC was stained.  This image demonstrated the spatial location of the RBC and shows that macrophase separation has occured.

The above image is unable to give any chemical information due the fact that the staining has masked out any small differences in chemistry.  To overcome this limitation, this blend was studied in the x-ray microscope and the micrographs obtained are shown below.

The left micrograph (a) was acquired at a photon energy highly absorbed by the matrix and the oval shapes of the RBC dispersions are clearly visible.  The right micrograph (b) was obtained at a photon energy not specific to either polymer and shows a "optical thickness" map.  The relative contrast between the two images is due to the relative absorption of the RBC.

To better understand the chemistry, x-ray absorption spectra were acquired from different areas within the samples.  These spectra are shown below.

These spectra were acquired from a) the homopolymer, b) the RBC, c) and d) two RBC dispersions within the blend.  Due to the similarity of the homopolymer and RBC the overall shape of the spectra is comparable, however differences occur about 288 eV (labeled by the arrow).  By careful comparison of spectra (b), (c) and (d) it is shown that the different dispersions contain different amounts of the homopolymer.

For More Information
Click here (PDF, 150 kbyte) for a reprint of the paper from this project which appeared in Macromolecules, vol 30, num 3, pages 663-666.

All materials here copyright 1998 by Dr. Harald Ade and the Polymer X-ray Spectromicroscopy Research Group.
Reproduction without permission and/or attribution  is prohibited (single print-out excepted). Reprint copyright Macromolecules and the American Chemical Society.

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Page created 11/15/98 by A. P. Smith.  Last modified 12/30/98.