We performed an experimental observation on the spontaneous imbibition of water in a porous media in a radial Hele-Shaw cell and confirmed Washburns law, where r is distance and t is time. Spontaneous imbibition with a radial interface window followe
d scaling dynamics when the front invaded into the porous media. We found a growth exponent (b{eta}=0.6) that was independent of the pressure applied at the liquid inlet. The roughness exponent decreased with an increase in pressure. The roughening dynamics of two dimensional spontaneous radial imbibition obey Family-Vicsek scaling, which is different from that with a one-dimensional planar interface window.
We report forced radial imbibition of water in a porous medium in a Hele-Shaw cell. Washburns law is confirmed in our experiment. Radial imbibition follows scaling dynamics and shows anomalous roughening dynamics when the front invades the porous med
ium. The roughening dynamics depend on the flow rate of the injected fluid. The growth exponents increase linearly with an increase in the flow rate while the roughness exponents decrease with an increase in the flow rate. Roughening dynamics of radial imbibition is markedly different from one dimensional imbibition with a planar interface window. Such difference caused by geometric change suggests that universality class for the interface growth is not universal.
We report the spontaneous generation of an Archimedean spiral pattern of fullerene via the evaporation of solvent. The self-organized spiral pattern exhibited equi-spacing on the order of micrometer between neighboring stripes. The characteristics of
the spirals, such as the spacing between stripes, the number of stripes and the band width of stripes, could be controlled by tuning the thickness of the liquid bridge and the concentration of solution. The mechanism of pattern formation is interpreted in terms of a specific traveling wave on the liquid-solid interface accompanied by a stick-slip process of the contact line.
In this article, we describe the instability of a contact line under nonequilibrium conditions mainly based on the results of our recent studies. Two experimental examples are presented: the self-propelled motion of a liquid droplet and spontaneous d
ynamic pattern formation. For the self-propelled motion of a droplet, we introduce an experiment in which a droplet of aniline sitting on an aqueous layer moves spontaneously at an air-water interface. The spontaneous symmetry breaking of Marangoni-driven spreading causes regular motion. In a circular Petri dish, the droplet exhibits either beeline motion or circular motion. On the other hand, we show the emergence of a dynamic labyrinthine pattern caused by dewetting of a metastable thin film from the air-water interface. The contact line between the organic phase and aqueous phase forms a unique spatio-temporal pattern characterized as a dynamic labyrinthine. Motion of the contact line is controlled by diffusion processes. We propose a theoretical model to interpret essential aspects of the observed dynamic behavior.
We report on a periodic precipitation pattern emerged from a drying meniscus via evaporation of a polystyrene solution in a Petri dish. It appeared a quasi-logarithmic spacing relation in the pattern as a result of stick-slip motion of the contact li
ne towards the wall. A model based on the dynamics of the evaporating meniscus is proposed.
We studied the curvature-driven roughening of a disk domain pattern with a variable interface window. The relaxation of interface is driven by negative surface tension . When a domain boundary propagates radially at a constant rate, we found that evo
lution of interface roughness follows scaling dynamic behavior. The local growth exponents are substantially different from the global exponents. Curvature-driven roughening belongs to a new class of anomalous roughening dynamics. However, a different surface tension leads to different global exponents. This is different from that of interface evolution with a fixed-size window, which has universal exponent. The variable growth window leads to a new class of anomalous roughening dynamics.
We report the generation of a dynamic labyrinthine pattern in an active alcohol film. A dynamic labyrinthine pattern is formed along the contact line of air/pentanol/aqueous three phases. The contact line shows a clear time-dependent change with rega
rd to both perimeter and area of a domain. An autocorrelation analysis of time-development of the dynamics of the perimeter and area revealed a strong geometric correlation between neighboring patterns. The pattern showed autoregressive behavior. The behavior of the dynamic pattern is strikingly different from those of stationary labyrinthine patterns. The essential aspects of the observed dynamic pattern are reproduced by a diffusion-controlled geometric model.
We report the generation of directed self-propelled motion of a droplet of aniline oil with a velocity on the order of centimeters per second on an aqueous phase. It is found that, depending on the initial conditions, the droplet shows either circula
r or beeline motion in a circular Petri dish. The motion of a droplet depends on volume of the droplet and concentration of solution. The velocity decreases when volume of the droplet and concentration of solution increase. Such unique motion is discussed in terms of Marangoni-driven spreading under chemical nonequilibrium. The simulation reproduces the mode of motion in a circular Petri dish.
We investigate the total flux density, spectral, polarization, and Faraday rotation variability of HST-1 in the M87 jet during the outburst from 2003 to 2007 through multi-epoch VLA observations at 8, 15, and 22 GHz. Contrary to the general case for
blazars, the flux densities of HST-1 rise earlier at lower frequencies from radio to X-ray, and the spectra are softening with the growth of outburst, indicating that the newly emerging subcomponents within HST-1 have relatively steep spectra. In particular, the intrinsic EVPA varies monotonically by $sim90^circ$ at the 3 wavebands during the period, and all but the stationary subcomponent in the eastern end of HST-1 move downstream superluminally deviating divergently from the overall jet direction, with the motion of the outmost subcomponent bending from one side of the jet axis to another. These strongly argue for the presence of helical magnetic fields around HST-1, which is also supported by the fact that the subcomponents might be accelerated in this region. The fractional polarization is relatively low in the rising stage, and in the decaying stage the polarization levels are almost comparable at the 3 wavebands. In view of the quite large RM values, Faraday rotation is expected to occur dominantly external to HST-1 in the decaying stage, which is well supported by the presence of diffuse emission around HST-1, and consistent with the scenario that RM decrease gets slower with time.
