ABSTRACT
Polyanilines (PANI)/reduced graphene oxide (RGO) nanocomposites are chemically synthesized. Their structure and morphology are characterized by scanning and transmission electron microscopies, x-ray diffraction and Raman spectroscopy. In addition, the nanocomposites' electrical, thermal and thermoelectric (TE) transport characteristics are investigated as a function of RGO content. The power factor and figure of merit (ZT) of PANI/RGO hybrids are deduced from measurements of the electrical conductivity (σ), Seebeck coefficient (α) and thermal conductivity (κ). Experimental results reveal that the properties of PANI/RGO composites are inherently dependent on the volume fraction of RGO. It is observed that electrical percolation follows a 2D conduction process which takes place for samples having 0.099 vol% RGO content. Unlike electrical conductivity, the thermal conductivity of PANI/RGO increases only slightly with the RGO fraction and is successfully fitted using a modified MG-EMA model which provides an interfacial (PANI/RGO nanoplatelets) resistance (Rk) of 4.9 × 10(-10) m(2) K W(-1). This low Rk value is attributed to good interactions between the planar geometry of RGO platelets and PANI aromatic rings through π-π stackings as evidenced by Raman spectroscopy and x-ray studies. Compared to that of pure PANI, the TE performance of PANI/RGO composites exhibits a ZT enhancement of two orders of magnitude.
ABSTRACT
Most alkyl phenyl sulfones are readily alpha-chlorinated with CCl(4) and alpha-brominated with CBrCl3 in KOH-t-BuOH via radical-anion radical pair (RARP) reactions. While isopropyl mesityl sulfone (4) is easily alpha-chlorinated with CCl(4), it was completely recovered when treated with the more reactive CBrCl3. Subsequent investigations showed the latter result to be due to the poor acidity of 4 together with the rapid depletion of CBrCl3 and KOH by their reaction with each other, and led to a variety of other important results. 4-Hydroxyphenyl isopropyl sulfone (6) is unreactive with either CCl4 or CBrCl3 in KOH-t-BuOH, its phenoxide anion strongly reducing the electronegativity of the sulfonyl group, thereby inhibiting alpha-anion formation. This effect is reversed by the electron-withdrawing influence of two alpha-phenyls, so that benzhydryl 4-hydroxyphenyl sulfone (8) is readily alpha-halogenated in KOH-t-BuOH with CCl4 or CBrCl3. On further contact with KOH-t-BuOH the alpha-halogenated sulfones from 8 are decomposed into benzophenone and phenol. While the alpha-halogenated derivatives of 4-methoxyphenyl benzhydryl sulfone (9) are stable to base, they are decomposed even under mildly acidic conditions into 4-methoxyphenyl 4-methoxybenzenethiolsulfonate (9c), phenol, and benzophenone. Mono-alpha-halogenation of benzyl phenyl sulfone (10) enhances the rate of the subsequent halogenation, so that alpha,alpha-dihalogenation is attained while much substrate is still present and the mono-alpha-halogenated product is not detected. The ease of reductive debromination of alpha-bromo sulfones with Cl3C- was correlated with the stability of the formed alpha-anions, explaining the success with alpha-bromobenzylic sulfones but failure with alpha-bromoalkyl sulfones. In the presence of air and the absence of competing halogenation, formation of the alpha-anions of alkyl aryl sulfones is quickly accompanied by oxidative cleavage by atmospheric O2, leading to the formation of arenesulfonyl alcohols, arenesulfonyl halides, and haloarenes.
