RESUMO
Crystallinity of the polymer poly(3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-altthieylenevinylene) (PDVF) adlayers casted from low-boiling-point (L-bp), medium-bp (M-bp), and high-bp (H-bp) solvents was investigated through scanning tunneling microscopy (STM) and analyzed by the assistance of Hansen solubility parameter (HSP) theory and molecular dynamics (MD) simulations. Crystallinity of the PDVF adlayers increases evidently from the L- to H-bp solvents. Also, the solvent with an alkyl chain such as ethylbenzene (EB) facilitates in improving the crystallinity than the one without an alkyl chain such as chlorobenzene (CB) if the solvent bp is present in the same group. The HSP space discloses that EB is a marginal solvent for PDVF in contrast to CB. Quasi-isolate PDVF in the EB solution revealed by MD simulations facilitates the formation of crystallized domains through surface assembling mechanism. However, in CB, interconnected PDVF molecules through intermolecular overlapping tend to generate amorphous structures through direct deposition of the preformed structures in solution.
RESUMO
An interconnected framework of reduced graphene oxide/phenyl formaldehyde polymer composites was synthesized by a one-pot hydrothermal reaction followed by carbonizing under different conditions. Then, the obtained porous materials with varied surface properties were used to disperse ultrasmall Pt nanoparticles. The catalyst with the optimized support demonstrates superior achievements to methanol oxidation reaction (MOR): distinctive improved mass activity (MA) and specific activity at both forward peak position and at the potential range near the operation of fuel cells, best antipoisonous ability revealed by 17 times MA and 7 times the retaining rate of commercial Pt/C in chronoamperometric evaluations, and outstanding long-term stability verified by 3-4 times MA and the retaining rate of Pt/C in the accelerated duration tests. By analyzing the performances of all studied catalysts, we proposed that fruitful oxygen groups and defects on the surface of supporting materials play a key role in boosting the MOR fulfillments through strengthening the Pt-substrate interaction or facilitating the removal of CO from the Pt surface. Elimination of surface oxygen groups and defects may promote the conductivity and mechanical strength of the catalysts but could result in a serious deterioration of antipoisonous ability, which means that only if the deliberate balance is achieved in the preparation of supporting materials can the MOR performances of Pt be improved synergistically.
RESUMO
Structural evolution of polymer (NTZ12) interface films during the process of annealing is revealed at the domain and single molecular levels using the statistical data measured from scanning tunneling microscopy images and through theoretical calculations. First, common features of the interface films are examined. Then, mean values of surface-occupied ratio, size and density of the domain are used to reveal the intrinsic derivation of the respective stages. Formation of new domains is triggered at 70 °C, but domain ripening is not activated. At 110 °C, the speed of formation of new domains is almost balanced by the consumption due to the ripening process. However, formation of new domains is reduced heavily at 150 °C but restarted at 190 °C. At the single molecular level, the ratio of the average length of linear to curved backbones is increased during annealing, whereas the ratios of the total length and the total number of linear to curved skeletons reaches a peak value at 150 °C. The two major conformations of curved backbones for all samples are 120° and 180° bending, but the ripening at 150 °C reduces 180° folding dramatically. Molecular dynamic simulations disclose the fast relaxing process of curved skeletons at high temperature.
