Controlling Materials Architecture on the Nanometer-Scale: PPV Nanocomposites Via Polymerizable Lyotropic Liquid Crystal
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with unique or superior bulk properties [3-6]. We have developed a general approach to synthetic nanocomposites with hexagonal symmetry using polymerizable lyotropic (i.e., amphiphilic) liquid crystals (LLC's) [7,8]. Our basic strategy entails the following steps: (1) Design and synthesis of cross-linkable amphiphiles that self-assemble into the inverse hexagonal phase in the presence of hydrophilic reagents instead of pure water. (2) Photopolymerization of the matrix monomers into an ordered template network with retention of the original architecture. (3) In situ conversion of the reagents dissolved in the hydrophilic channels into solid "filler" materials in order to achieve the final composite. Both inorganic [7] and organic chemistry [8] can be performed inside the ordered hydrophilic domains, and the resulting nanocomposites can be shaped into films, fibers, etc. prior to cross-linking. In order to investigate the effects of nanometer-scale engineering on the photophysical properties of encapsulated materials, we recently synthesized poly(p-phenylenevinylene) (PPV) inside the hydrophilic channels of the LLC phase formed by monomer 1 (Figure 1) [8]. PPV was chosen as the "filler" in this initial investigation because it is formed from a water-soluble precursor, and PPV and its derivatives have recently been used in a number of device applications [9,10]. The resulting nanocomposites have regular interchannel spacing of 4 nm and exhibit enhanced, blue-shifted fluorescence compared to that of pure PPV. In this paper, we present preliminary results on controlling the small-scale architecture of these composites through (1) choice of the metal ion on the headgroup of the monomer and (2) variation of the tail length. The incorporation of transition-metal and lanthanide cations also provides a simple 419 Mat. Res. Soc. Symp. Proc. Vol. 488 © 1998 Materials Research Society
means of introducing a variety of interesting properties into these nanostructured materials.
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O(CH 2) 1 1OOCCH=CH 2 Na+ -OO-.-ý O(CH 2)llOOCCH=CH2 O(CH 2)1lOOCCH=CH2
+ .
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-en SMe A 2" -n HCI
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Fig. 1. Synthetic scheme for formation of PPV nanocomposites with hexagonal symmetry. EXPERIMENTAL General. All reagents and solvents were obtained from the Aldrich Chemical Co., Fisher Scientific, or Sigma Chemicals, and purified before use. Monomer 1 was prepared according to literature procedures (see Supporting Information of Ref. [8]). All syntheses were performed under inert atmosphere. Low angle X-ray diffraction studies were performed using an Inel CPS 120 powder diffraction system employing Cu Ka radiation. Fluorescence measurements were performed on a Spex Fluoromax 2. Elemental analyses were performed at Galbraith Laboratories, Knoxville, TN. Quantum yields were measured in the laboratory of Prof. G. Leising at the Technische Universitdt, Graz, Austria. Typical preparation of transition-metal or lanthanide-containing LLC. Compound 1 (1.00 g, 1.16 mmol) was dissolved in a mixture of acetone (100 rmL) and methanol (10
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