Crystallization of isotactic polypropylene under the spatial confinement templated by block copolymer microdomains.

We investigate the crystallization behavior of isotactic polypropylene (iPP) under the influence of nanoscale confinement templated by the microphase-separated structure of an iPP-based diblock copolymer system, isotactic polypropylene-block-atactic polystyrene (iPP-b-aPS). Three types of iPP microdomains, i.e., lamellae, cylinder, and sphere, were generated by controlling the composition of the diblock. The effect of microdomain morphology on the nucleation mechanism, crystallization kinetics, self-nucleation behavior, the population of the helical sequence of iPP block in the melt state, and crystal orientation have been systematically studied. It was found that the crystallization rate of iPP was predominantly controlled by homogeneous nucleation when the crystallization process was largely confined within the individual cylindrical and spherical microdomains. Such a nucleation mechanism and the highly frustrated crystal growth in the isolated microdomains led to the absence of Domain II and atypical crystallization kinetics in Domain III in the self-nucleation study. The population of the longer helical sequence of iPP block revealed by infrared spectroscopy was found to be affected by temperature but not by the spatial confinement, chain stretching, and junction point constraint imposed by the microdomains. Finally, the orientation of α-form iPP crystals in the lamellae-forming iPP-b-aPS was identified over a broad range of crystallization temperatures (T(c)). Different from other crystalline-amorphous diblocks, a lamellar branching of α-form iPP was observed in the lamellar microdomains at T(c) lying between 15 and 80 °C, where the daughter lamellae developed from the perpendicularly orientated parent iPP crystals with a specific angle of 80° or 100°. Once the sample was crystallized at T(c) ≤ 10 °C, the iPP crystals became randomly oriented.

Critical analysis of the crystal orientation behavior in polyethylene-based crystalline-amorphous diblock copolymer.

Orientation of polyethylene (PE) crystals formed over a broad range of undercooling in a polyethylene-block-poly(D,L-lactide) (PE-b-PDLLA) diblock copolymer has been critically examined. Due to the large segregation strength and approximate 50/50 composition in this system, the crystallization took place within one-dimensionally confined lamellar microdomains without forming spherulites. A homogeneous crystal orientation with the PE crystalline stems orienting parallel to the lamellar interface was observed at crystallization temperatures (T(c)) between 45 and 102 °C. Once the sample was crystallized at T(c) ≤ 40 °C or directly quenched into liquid nitrogen from the melt, the isotropic WAXD pattern indicated that the PE crystals became randomly oriented. Considering that homeotropic orientation was not identified for the present system and other PE-based crystalline-amorphous diblocks, we concluded that PE crystals in the lamellar microdomains always show homogeneous orientation when there is a preferred orientational order. We further organized the thermodynamic and kinetic factors that may govern the preferred crystal orientation in diblock copolymers and concluded that the orientational order should be controlled by the competition between nucleation and crystal growth kinetics. The persistence of homogeneous orientation of PE was attributed to its excellent nucleating power.

Design and tailoring of the nanotubular arrayed architecture of hydrous RuO2 for next generation supercapacitors.

By use of the membrane-templated synthesis route, hydrous RuO2 (RuO2.xH2O) nanotubular arrayed electrodes were successfully synthesized by means of the anodic deposition technique. The desired three-dimensional mesoporous architecture of RuO2.xH2O nanotubular arrayed electrodes with annealing in air at 200 degrees C for 2 h simultaneously maintained the facility of electrolyte penetration, the ease of proton exchange/diffusion, and the metallic conductivity of crystalline RuO2, exhibiting unexpectedly ultrahigh power characteristics with its frequency "knee" reaching ca. 4.0-7.8 kHz, 20-40 times better than that of RuO2 single crystalline, arrayed nanorods. The specific power and specific energy of annealed RuO2.xH2O nanotubes measured at 0.8 V and 4 kHz is equal to 4320 kW kg-1 and 7.5 W h kg-1, respectively, demonstrating the characteristics of next generation supercapacitors.