Functional mesoporous carbons have attracted significant scientific and technological interest owning to their fascinating and excellent properties. However, controlled synthesis of functional mesoporous carbons with large tunable pore sizes, small particle size, well-designed functionalities, and uniform morphology is still a great challenge. Herein, we report a versatile nanoemulsion assembly approach to prepare Ndoped mesoporous carbon nanospheres with high uniformity and large tunable pore sizes (5−37 nm). We show that the organic molecules (e.g., 1,3,5-trimethylbenzene, TMB) not only play an important role in the evolution of pore sizes but also significantly affect the interfacial interaction between soft templates and carbon precursors. As a result, a welldefined Pluronic F127/TMB/dopamine nanoemulsion can be facilely obtained in the ethanol/water system, which directs the polymerization of dopamine into highly uniform polymer nanospheres and their derived N-doped carbon nanospheres with diversely novel structures such as smooth, golf ball, multichambered, and dendritic nanospheres. The resultant uniform dendritic mesoporous carbon nanospheres show an ultralarge pore size (∼37 nm), small particle size (∼128 nm), high surface area (∼635 m 2 g −1 ), and abundant N content (∼6.8 wt %), which deliver high current density and excellent durability toward oxygen reduction reaction in alkaline solution.
Chain
entanglement was very important for adjusting the processability
and mechanical property of nascent ultrahigh molecular weight polyethylene
(UHMWPE). So far, it is still a mystery to unravel the formation mechanism
of entanglements when the ethylene polymerization is conducted by
the heterogeneous catalysts. In this study, a series of weakly entangled
UHMWPE was synthesized by the polyhedral oligomeric silsesquioxane/MgCl2 nanoaggregates modified Ziegler–Natta catalysts. The
structure of nanoaggregates was evaluated by X-ray photoelectron spectroscopy,
density functional theory simulations, and scanning probe microscope
experiments, where the coordination strategy of MgCl2 and
hydroxyl of POSS was investigated. These nanoaggregates presented
extremely low activity on ethylene polymerization and were proved
to serve as isolators for separating the active sites and growing
chains. The entanglement density of nascent UHMWPE (reflected by the
value of initial storage modulus G′(t=0)) was exponentially decayed with the polymerization
activity of increased numbers of nanoaggregates. Importantly, this
exponentially decayed effect contributed by increased numbers of POSS/MgCl2 isolators offset the rapid power function increment of entanglements
upon rising the temperature, which was the essential reason for the
successful synthesis of weakly entangled UHMWPE even at 85 °C.
Finally, we have proposed the dependence and sensitivity of G′(t=0) (i.e., indicating
the initial entanglement density of nascent polymers) on the polymerization
activity, which was able to trace the formation of entanglements during
polymerization through the POSS modified heterogeneous catalyst.
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