Thermoreversible Changes in Aligned and Cross-Linked Block Copolymer Melts Studied by Two Color Depolarized Light Scattering

Journal Article · Tue Sep 04 00:00:00 EDT 2012 · Macromolecules

DOI:https://doi.org/10.1021/ma300860g· OSTI ID:1052883

Wilbur, Jeffrey D. ^[1]; Gomez, Enrique D. ^[2]; Ellsworth, Mark W. ^[3]; Garetz, Bruce A. ^[4]; Balsara, Nitash P. ^[2]

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1. Univ. of California, Berkeley, CA (United States)
2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
3. TAMKO Building Products, Inc., Joplin, MI (United States)
4. Polytechnic Inst. of NYU, Brooklyn, NY (United States)

A procedure for creating samples that can be repeatedly cycled between weakly aligned and strongly aligned states is described. Poly(styrene-b-isoprene) block copolymer samples were first shear-aligned and then cross-linked using a high energy electron beam. Samples with more than 1.0 cross-links per chain on average showed almost complete recovery of their initial alignment state even after 20 cycles of heating above the order–disorder transition temperature of the un-cross-linked block copolymer. Samples with 1.1 cross-links per chain, which showed over 90% loss of alignment on heating and almost 100% recovery of alignment on cooling, provided the best example of a reversible aligned-to-unaligned transition. Samples with lower cross-linking densities exhibited irreversible loss of alignment upon heating, while those with higher cross-linking densities exhibited less than 90% loss of alignment upon heating. Alignment was quantified by a technique that we call two color depolarized light scattering (TCDLS), an extension of the traditional depolarized light scattering experiment used to determine the state of order in block copolymers. Qualitative confirmation of our interpretation of TCDLS data was obtained by small-angle X-ray scattering and transmission electron microscopy.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: USDOE; National Science Foundation (NSF)
• OSTI ID: 1052883
• Journal Information: Macromolecules, Vol. 45, Issue 18; ISSN 0024-9297
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: ENGLISH