Hierarchical assembly of diphenylalanine into dendritic nanoarchitectures.

Highly ordered, multi-dimensional dendritic nanoarchitectures were created via self-assembly of diphenylalanine from an acidic buffer solution. The self-similarity of dendritic structures was characterized by examining their fractal dimensions with the box-counting method. The fractal dimension was determined to be 1.7, which demonstrates the fractal dimension of structures generated by diffusion limited aggregation on a two-dimensional substrate surface. By confining the dendritic assembly of diphenylalanine within PDMS microchannels, the self-similar dendritic growth could be hierarchically directed to create linearly assembled nanoarchitectures. Our approach offers a novel pathway for creating and directing hierarchical nanoarchitecture from biomolecular assembly.

A study on electrophoretic deposition of Ni nanoparticles on pitted Ni alloy 600 with surface fractality.

In the present work, the electrophoretic deposition of Ni nanoparticles used for self-repairing of pits in organic suspension was investigated on pitted fractal Ni alloy 600 with respect to surface fractality of the pits. For this purpose, Ni nanoparticles prepared by levitation-gas condensation were dispersed into an ethanol solution with the addition of a dispersant. Four kinds of pitted fractal specimens with different surface fractal dimensions dF,surf were prepared by applying various anodic potentials above pitting potential to alloy 600 in aqueous 0.1 M NaCl solution. From the scanning electron microscopy (SEM) images, it was observed that the pits repaired under applied electric field E of 100 V cm-1 comprised more agglomerates of Ni nanoparticles than those repaired under E of 20 V cm-1. This suggests that the higher the value of E is, the more agglomerates of Ni nanoparticles are deposited on the specimen due to more depletion of OH- in suspension near the specimen surface. Moreover, the specimen with higher dF,surf gave a higher value of electrophoretic current Ip than one with lower dF,surf due to the increased electrochemical active area Aea of the specimen. From the above, it is concluded that the surface irregularities of the pit enhance the deposition of Ni nanoparticles on pitted fractal specimen during electrophoretic deposition.

Theoretical approach to ion penetration into pores with pore fractal characteristics during double-layer charging/discharging on a porous carbon electrode.

The effects of pore fractal characteristics on the kinetics of double-layer charging/discharging on a porous carbon electrode were investigated by using theoretical calculations of potentiostatic current transients (PCTs) and cyclic voltammograms (CVs). Prior to theoretical calculation, it was experimentally evidenced that pore fractality is clearly possessed by the porous carbon electrode. From the analyses of the PCTs and the CVs theoretically calculated at various values of pore fractal dimension dF,pore, inner cutoff length rmin, and outer cutoff length rmax of the pore fractality, it was found that as dF,pore increased, the absolute values of the derivatives of the logarithmic PCTs decreased to 0.5, and the current decayed more slowly with time. The rate capability gamma decreases with increasing dF,pore over the whole scan-rate range, which leads to the lower power density. As rmin increased, the current decayed more rapidly in the later stage of the PCT, which is mainly limited by the smaller pores. On the other hand, as rmax increased, the current decayed more rapidly in the earlier stage of the PCT, which is mainly determined by the larger pores. Moreover, the larger values of rmin and rmax enhance the rate capability gamma as well, but they reduce the double-layer capacitance. The beneficial contribution of the larger pores to the power density competes with the detrimental contribution of those pores to the energy density.