John A Pople

Publications (2)13.2 Total impact

• Article: Morphology and Thermodynamic Properties of a Copolymer with an Electronically Conducting Block: Poly(3-ethylhexylthiophene)-block-poly(ethylene oxide).

  Shrayesh N Patel, Anna E Javier, Keith M Beers, John A Pople, Victor Ho, Rachel A Segalman, Nitash P Balsara
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  ABSTRACT: We report on the synthesis and morphology of a block copolymer, poly(3-(2'-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), that conducts both electrons and ions. We show that in the melt state the P3EHT-b-PEO chains self-assemble to produce traditional nanoscale morphologies such as lamellae and gyroid. This is in contrast to a majority of previous studies on copolymers with electronically conducting blocks wherein a nanofibrillar morphology is obtained. Our approach enables estimation of the Flory-Huggins interaction parameter, χ. The segregation strength between the two blocks is controlled through the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For the salt-free sample, the gyroid morphology, obtained in the melt state, is transformed into lamellae below the melting temperature of the P3EHT block. This is due to the "breaking out" of the crystalline phase. For the salt-containing sample, P3EHT-b-PEO has a lamellar morphology in both melt and crystalline states (confined crystallization).
  Nano Letters 07/2012; 12(9):4901-6. · 13.20 Impact Factor
• Article: Phase Behavior of Polystyrene-block-poly(2-vinylpyridine) Copolymers in a Selective Ionic Liquid Solvent

  Justin M. Virgili, Alexander Hexemer, John A. Pople, Nitash P. Balsara, Rachel A. Segalman
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  ABSTRACT: The phase behavior of poly(styrene-block-2-vinylpyridine) copolymer solutions in an imidazolium bis(trifluoromethane)sulfonamide ([Im][TFSI]) ionic liquid has been studied using small-angle X-ray scattering (SAXS) and optical transmission characterization. Through scaling analysis of SAXS data, we demonstrate that the [Im][TFSI] ionic liquid behaves as a selective solvent toward one of the blocks. We observe lyotropic and thermotropic phase transitions that correspond qualitatively to the phase behavior observed in block copolymer melts and block copolymer solutions in molecular solvents. In addition, we have studied the thermal properties of block copolymer solutions in the ionic liquid using differential scanning calorimetry and wide-angle X-ray scattering. We observe distinct composition regimes corresponding to the change in the block copolymer’s glass transition temperature, Tg, with respect to the concentration of polymer in ionic liquid. At high block copolymer concentrations, a “salt-like” regime corresponding to an increase in the block copolymer Tg is observed, while at intermediate block copolymer concentrations, a “solvent-like” regime corresponding to a decrease in the block copolymer Tg is observed. An unusual thermal transition consisting of crystallization and subsequent melting of the ionic liquid is observed at the lowest block copolymer concentration characterized.
  07/2009;