Liquid Crystalline, Semifluorinated Side Group Block Copolymers with Stable Low Energy Surfaces:  Synthesis, Liquid Crystalline Structure, and Critical Surface Tension

Abstract

Monodisperse poly(styrene-b-semifluorinated side chain) block copolymers were synthesized by anionic polymerization of poly(styrene-b-1,2/3,4-isoprene) followed by the corresponding polymer analogous reactions. By controlling the block copolymer composition and the relative lengths of the fluorocarbon and hydrocarbon units in the side group, the effect of chemical structure on surface properties and the influence of liquid crystalline structure of the semifluorinated side chain on the surface behavior were evaluated. The composition of side groups does not greatly affect the as-prepared sample surface tension, but influences instead the transition temperatures of the room temperature liquid crystal phase. It was observed that the shorter fluorocarbon units (six −CF2− units) form a smectic A phase at room temperature. The critical surface tension of the SA phase is 10.8 mN/m, and the polymer surface undergoes significant reconstruction when immersed in water. However, when the fluorocarbon side chain contains more than eight −CF2− units, the resulting surface possesses a lower critical surface tension (ca. 8 mN/m) and exhibits negligible surface reconstruction. We believe the stability results from the highly ordered packing of the room temperature smectic B phase. This mesophase resists the reconstruction of the surface, since to do so would require loss of the enthalpies of transition. The estimated activation energy to destroy the smectic B phase is about 3−10 times higher than that of smectic A phase. This phase forms a uniform, hexagonally packed −CF3 terminated surface with a low critical surface tension similar to that of fluorocarbon-based Langmuir−Blodgett films. The self-assembly of these liquid crystalline block copolymers at both the molecular and microstructural level provides a valuable approach to creating stable, low surface energy materials.

Temperature dependant structural changes in thin films of random semifluorinated PMMA copolymers

“…Semifluorinated (SF) side chain polymers show a structure behaviour which is characterized by phase separation between polymer backbone and SF side chains (e.g., Höpken and Möller, 1992;Wang et al, 1997), driven by huge Flory-Huggins interaction parameters. As a result of the strong interaction between the fluorinated segments, e.g.…”

Understanding and controlling the morphology of styrene–isoprene side-group liquid crystalline diblock copolymers

“…Work conducted collaboratively by the Ober (Cornell) and Thomas (MIT) groups has focused on both LC rodamorphous coil block copolymers [19][20][21][22][23] and amorphous side-group LC-amorphous coil block copolymers [6,15,19,20,24], as well as fluorinated side group LC copolymers [25]. The structure of the azobenzene mesogen based stryene-isoprene side-group LC diblock is shown in Fig.…”

Molecular basis for solvent dependent morphologies observed on electrosprayed surfaces

“…However, for surface applications focusing on hydrophobicity, copolymers of fluorinated and conventional monomers can be effectively employed since the fluorinated groups segregate at the solid-air interface to decrease surface energy. 1,[7][8][9] In addition, self-assembly of fluorinated block copolymers in various environments has been successfully utilized to fabricate nano-structures having a wide range of morphologies which have found applications in emerging technologies such as nano-optics, nano-electronics and nanobiotechnology. 10,11 Low surface energy of the fluorinated polymers is commonly utilized in the area of superhydrophobicity, a subject that became popular when the naturally micro-textured surface of the non-wettable lotus leaves was discovered.…”