| Abstract
| - Monodisperse poly(styrene-b-semifluorinated sidechain) block copolymers were synthesizedby anionic polymerization ofpoly(styrene-b-1,2/3,4-isoprene) followed by thecorresponding polymeranalogous reactions. By controlling the block copolymercomposition and the relative lengths of thefluorocarbon and hydrocarbon units in the side group, the effect ofchemical structure on surface propertiesand the influence of liquid crystalline structure of thesemifluorinated side chain on the surface behaviorwere evaluated. The composition of side groups does not greatlyaffect the as-prepared sample surfacetension, but influences instead the transition temperatures of the roomtemperature liquid crystal phase.It was observed that the shorter fluorocarbon units (six−CF2− units) form a smectic A phase atroomtemperature. The critical surface tension of the SAphase is 10.8 mN/m, and the polymer surface undergoessignificant reconstruction when immersed in water. However, whenthe fluorocarbon side chain containsmore than eight −CF2− units, the resulting surfacepossesses a lower critical surface tension (ca. 8 mN/m) and exhibits negligible surface reconstruction. We believe thestability results from the highly orderedpacking of the room temperature smectic B phase. This mesophaseresists the reconstruction of thesurface, since to do so would require loss of the enthalpies oftransition. The estimated activation energyto destroy the smectic B phase is about 3−10 times higher than thatof smectic A phase. This phaseforms a uniform, hexagonally packed −CF3 terminatedsurface with a low critical surface tension similarto that of fluorocarbon-based Langmuir−Blodgett films. Theself-assembly of these liquid crystallineblock copolymers at both the molecular and microstructural levelprovides a valuable approach to creatingstable, low surface energy materials.
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