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Large-Area Three-Dimensional Molecular Ordering of a Polymer Brush by One-Step Processing

Science  05 Nov 2010:
Vol. 330, Issue 6005, pp. 808-811
DOI: 10.1126/science.1195302

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Bend It, Stretch It

Materials (such as those found in some artificial muscle systems) that are used for stimulus-controlled bending or stretching, require long-range ordering so that local chemical triggers will result in long-range bending or flexing motions. Hosono et al. (p. 808) observed that a sandwich of a polymethacrylate between uniaxially stretched Teflon sheets develops three-dimensional ordering. Upon hot pressing, the main chains of the polymer brushes aligned homeotropically to the film plane, whereas the side chains, containing azobenzene groups, oriented horizontally along the drawing direction of the Teflon sheets. With some azobenzene groups, alternate irradiation with ultraviolet and visible light made the composites bend and stretch reversibly.

Abstract

Rational molecular design and processing, enabling large-area molecular ordering, are important for creating high-performance organic materials and devices. We show that, upon one-step hot-pressing with uniaxially stretched Teflon sheets, a polymer brush carrying azobenzene-containing mesogenic side chains self-assembles into a freestanding film, where the polymer backbone aligns homeotropically to the film plane and the side chains align horizontally. Such an ordered structure forms through translation of a one-dimensional molecular order of the Teflon sheet and propagates from the interface macroscopically on both sides of the film. The resultant wide-area bimorph configuration allows the polymer film to bend rapidly and reversibly when the azobenzene units are photoisomerized. The combination of polymer brushes with hot-pressing and Teflon sheets provides many possibilities in designing functional soft materials.

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