The phase behavior of the binary system consisting of the commercial nucleating and clarifying agent 1,3:2,4-bis(3,4-dimethyldibenzylidene)sorbitol (DMDBS, Millad 3988) and isotactic polypropylene (i-PP) was investigated over the entire concentration range by means of differential scanning calorimetry (DSC), rheology, and optical microscopy. Experimental phase diagrams were constructed from data obtained in melting and crystallization studies, and a simple binary monotectic is advanced. Distinct regimes in the phase diagram, which apparently dictate nucleation and clarification of i-PP by DMDBS, are discussed. A maximum increase in the crystallization temperature of i-PP due to the nucleating action of DMDBS was observed in compositions containing between 0.2 and 1 wt % of the latter. Liquid−liquid phase separation was observed at elevated temperatures for i-PP/DMDBS mixtures comprising more than 2 wt % of DMDBS. A study of the optical properties of the i-PP/DMDBS system revealed that values for haze and clarity of injection-molded plaques progressively decreased and increased, respectively, in the concentration range between 0.2 and 1 wt % DMDBS in i-PP; at DMDBS concentrations exceeding 1 wt % the presence of the additive had an adverse effect on the optical properties of i-PP. Finally, a surprisingly strong influence of cooling kinetics on the phase behavior and, consequently, on the optical properties of the i-PP/DMDBS system was detected, which is of obvious relevance for industrial applications.

We report the discovery of a family of organic compounds, substituted 1,3,5-benzenetrisamides, thatsdepending on subtle details of their chemical structuresare capable of selectively and extremely efficiently nucleating the growth of the common R-crystal modification of the major industrial polymer isotactic polypropylene (i-PP), rendering this normally turbid material highly transparent ("clarified") at exceedingly low concentrations (as low as a weight fraction of 0.0002), inducing the mechanically distinct, tough i-PP β-polymorph, or promoting growth of hybrids of both crystallographic modifications with heretofore unknown combinations of the above desirable optical-mechanical properties. In addition, these trisamide-based compounds exhibit excellent thermal stability and do not feature absorption of visible light, adding to a most favorable set of characteristics that provides marked benefits over the presently employed nucleating/clarifying agents.

A novel method to produce gas diffusion layers with patterned wettability for fuel cells is presented. The local irradiation and subsequent grafting permits full design flexibility and wettability tuning, while modifying throughout the whole material thickness. These water highways have improved operando performance due to an optimized water management inside the cells.

light-harvesting active layer is composed of bulk-heterojunctions, i.e., blends of a polymeric electron-donor (hole-conductor) and an electron-acceptor (electron-conductor), with fullerene derivatives yielding particularly promising results. Thanks to recent advances in the synthesis of donor materials, power-conversion effi ciencies of 8-10% can now be achieved with lab-scale devices. [ 1 ] The precise bulk-heterojunction nanostructure, i.e., the distribution of donor and acceptor molecules, is crucial for maximizing the photovoltaic performance for a given blend composition. This is because a compromise has to be made between two critical aspects: i) a large contact area between donor and acceptor molecules aids charge generation and thus a fi nely intermixed blend is favored, and ii) percolation of separated, relatively phase-pure donor and acceptor domains to improve charge transport to the electrodes. Therefore, the ideal nanostructure features an intermediate degree of phase separation, which has to be carefully optimized through processing parameters such as the choice of solvent or solvent mixture, the blend stoichiometry and polymer molecular weight as well as post-deposition thermal or vapor annealing.The bulk-heterojunction nanostructure of non-crystalline polymer:fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non-crystalline thiophene-quinoxaline copolymer and the widely used fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). To this end, C 60 fullerene is employed to effi ciently nucleate PCBM crystallization. Sub-micrometersized fullerene crystals are formed when as little as 2 wt% C 60 with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C 60 . Solar cells based on C 60 -nucleated blends indicate signifi cantly improved thermal stability of the bulk-heterojunction nanostructure even after annealing at an elevated temperature of 130 °C, which lies above the glass transition temperature of the blend. Moreover, we fi nd that various other compounds, including C 70 fullerene, single-walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents-commonly used to clarify isotactic polypropylene-permit to control crystallization of the fullerene phase.

No abstract