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Ordering transition of block copolymer films
1Department of Chemical Engineering and Texas Material Institute, The University of Texas at Austin, Austin, Texas 78712, USA.
The Journal of Physical Chemistry. B
|July 21, 2006
Summary
Thin film diblock copolymers exhibit increased ordering temperatures compared to bulk materials. Compressed CO2 environments further enhance ordering, contrary to expectations for small molecule diluents.
Area of Science:
- Polymer Science
- Materials Science
- Thin Film Physics
Background:
- Bulk symmetric A-b-B diblock copolymers form lamellar morphology below the order-disorder transition (ODT) temperature.
- The Flory-Huggins interaction parameter (chi) and degree of polymerization (N) govern copolymer ordering.
Purpose of the Study:
- Investigate the ODT of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) thin films.
- Compare thin film ODT with bulk material behavior.
- Examine the effect of compressed CO2 environments on thin film ordering.
Main Methods:
- Fabrication of PS-b-PMMA thin films on SiO(x)/Si substrates.
- Analysis of thin film ordering temperatures in vacuum and compressed CO2 environments.
- Estimation of temperature shifts related to chiN changes.
Main Results:
- Thin film diblock copolymers show increased ordering temperatures compared to bulk.
- Small changes in chiN correlate with significant shifts in the ODT.
- Compressed CO2 environments promote ordering at temperatures where films are disordered in vacuum.
Conclusions:
- Thin film confinement alters copolymer ordering behavior.
- Compressed CO2 acts as a structure-directing agent, enhancing ordering in thin films.
- Findings challenge the conventional understanding of diluent effects on copolymer ODT.