NEAR RAPID DIRECTIONAL SOLIDIFICATION AND ITS SUPERFINE MICROSTRUCTURE

This paper briefly reviews the recent research on the near rapid directional solidification and microstructure superfining. The morphology transitions and the corresponding mechanical properties are presented. The critical velocities relevant to the morphology transitions are comprehensively given. Meanwhile the solidification characteristics near absolute stability limit are studied.It can be clearly seen that the superfine microstructures possess extremely better properties compared with the conventional microstructures.

Energy stored in nanoscale water capillary bridges formed between chemically heterogeneous surfaces with circular patches

The formation of nanoscale water capillary bridges(WCBs) between chemically heterogeneous(patchy) surfaces plays an important role in different scientific and engineering applications, including nanolithography, colloidal aggregation, and bioinspired adhesion. However, the properties of WCB of nanoscale dimensions remain unclear. Using molecular dynamics simulations, we investigate the geometrical and thermodynamic properties of WCB confined between chemically heterogeneous surfaces composed of circular hydrophilic patches on a hydrophobic background. We find that macroscopic capillary theory provides a good description of the WCB geometry and forces induced by the WCB on the confining surfaces even in the case of surface patches with diameters of only 4 nm. Upon stretching, the WCB contact angle changes from hydrophobic-like values(θ > 90°) to hydrophilic-like values(θ < 90°) until it finally breaks down into two droplets at wall separations of ~9–10 nm. We also show that the studied nanoscale WCB can be used to store relevant amounts of energy EPand explore how the walls patch geometry can be improved in order to maximize EP. Our findings show that nanoscale WCB can, in principle, be exploited for the design of clean energy storage devices as well as actuators that respond to changes in relative humidity. The present results can also be of crucial importance for the understanding of water transport in nanoporous media and nanoscale engineering systems.

Highly uniform ultrasound-sensitive nanospheres produced by a pH-induced micelle-to-vesicle transition for tumor-targeted drug delivery

Although gas-filled microbubbles with high echogenicity are widely applied in clinical ultrasonography, the micron scale particle size impedes their use in the treatment of solid tumors, which are accessible to objects less than several hundred nanometers. We herein propose an unusual approach involving a pH-induced core-shell micelle-to-vesicle transition to prepare ultrasound-sensitive polymeric nanospheres （polymersomes in structure） possessing multiple features, including nanosize, monodispersity, and incorporation of a phase- transitional imaging agent into the aqueous lumen. These features are not achievable via the conventional double-emulsion method for polymersome preparation. The nanospheres were constructed based on a novel triblock copolymer with dual pH sensitivity. The liquid-to-gas phase transition of the imaging agent induced by external low-frequency ultrasound may destroy the nanospheres for a rapid drug release, with simultaneous tissue-penetrating drug delivery inside a tumor. These effects may provide new opportunities for the development of an effective cancer therapy with few adverse effects.

Biphenyl-Induced Superhelix in L-Phenylalanine-Based Supramolecular Self-Assembly with Dynamic Morphology Transitions

Dynamic transitions of supramolecular assemblies between lower-order structures and higher-order superhelical structures(e.g.,double-helical DNA,helical biopolymers)are of vital importance in many physiological processes,but still remain a great challenge to be realized in artificially assembled systems.Herein,a novel biphenyl central core symmetrically coupled with phenylalanine groups drives the construction of the dynamic superhelix.

One-step laser induced conversion of a gelatin-coated polyimide film into graphene:Tunable morphology,surface wettability and microsupercapacitor applications

Latest advances have witnessed the laser induction process on polyimide(PI)films for the formation of porous graphene.Herein,a fully converted graphene film was prepared by Nd:YAG laser scribing a gelatin coated PI film.It was found that the gelatin played the role of"shield"well in absorbing intense laser impact and benefit for the surface morphology modulation.Laser treatment lower than a critical fluence point of~4.00 J mm^(-2) contributed to a crater-like surface morphology due to the dispersed nature of Nd:YAG laser beam.By tuning laser fluence above the threshold,carbonized surface turned into continuous morphology.A fluid dynamics process accompanied by outgassing occurred during the carbonization,and the surface morphology gradually varied from stretched droplets to porous strips and finally to amorphous porous structures.The morphology evolution in combination with surface chemistry is responsible for the significant wettability transition from superhydrophobic to superhydrophilic,and a Janus superhydrophobic/superhydrophilic surface wettability was achieved under a laser fluence of~8.00 J mm^(-2).Eventually,microsupercapacitors(MSCs)were fabricated to show the great potential of our prepared graphene in flexible electronics.