Periodicity behavior was observed after droplet collision in viscous solutions with controlled glycerol concentrations onto a PDMS surface. No periodic movement was observed in the droplets at glycerol concentrations of 50% or more. In contrast, the vertical diameter of the droplets increased and decreased periodically at glycerol solution concentrations of 40% or less. Moreover, there was little change in the periodicity of the impacting droplet movement, and the vibration frequency was measured at approximately 80 to 98 Hz in the entire range. The maximum droplet spreading factor after collision decreased significantly with increasing glycerol concentrations of 40% or more (Ohnesorge number 1.4 × 10^-2 or more). The results suggest that the effect of viscosity became greater than that of the solution surface tension with increasing glycerol concentrations.

Superhydrophobicity and anisotropic wettability can be simultaneously achieved by simple groove pattern on a surface. To verify those characteristics experimentally, we fabricated the micro-grooved surfaces with four different groove widths. Static contact angles were measured with the sessile drop method to investigate the apparent wettability and wetting states. All four surfaces exhibited the static contact angles well fitted to those estimated on the Cassie-Baxter state in which favorable water-repellency was expected. The static contact angles measured perpendicular to grooves were higher than those measured parallel to grooves. This anisotropic wettability was also observed with the sliding angle at the onset of the droplet moving when the surfaces were tilted. The sliding angles measured perpendicular to grooves were much higher than those measured on the smooth surface without micro-grooves. Conversely, the sliding angles measured parallel to grooves were smaller than those measured on the smooth surface. Because the sliding angle as well as the contact angle hysteresis reflect the water-repellency, the micro-grooves clearly made the surfaces anisotropic water-repellent.

This paper presents results for effects of the liquid surface tension on the ejected droplet volume using a pneumatic printing system. The low surface tension of the solution causes the liquid wetting around the nozzle, and then the wetted nozzle also inhibits stable formation of droplets. First, we confirmed the maximum inlet pressure (i.e., balanced with capillary force on the outlet channel) corresponding to varied surface tensions of the solutions, prepared by controlling the concentration of a surfactant. The ejected droplet volumes with the surfactant concentrations was varied within approximately 7% at each maximum inlet pressure, and the volume variation decreased to a fifth as compared with a high surface tension liquid.

In this study, we fabricated the superhydrophobic and super-water-repellent surface with the micro/nano scale structures using simple conventional silicon wet-etching technique and the black silicon method by deep reactive ion etching. These fabrication methods are simple but very effective. Also we reported the droplet impact experimental results on the micro/nano-scaled surface. There are two representative impact behaviors as “rebound” and “fragmentation”. We found the transition Weber number between “rebound” and “fragmentation” statements, experimentally. Additionally, we concerned about the dimensionless spreading diameters for our super-water-repellent surface. The novel characterization method was introduced for analysis including the “fragmentation” region. As a result, our super-water-repellent surface with the micro/nano-scaled structures shows the different impact behaviors compared with a reference smooth surface, by some meaningful experiments.

This paper presents results for dispensing and measuring micro-particles using a pneumatic dispensing system. Particle-suspended liquid droplets were dispensed and analyzed quantitatively at various particle concentrations and applied pressures. By using a developed experimental setup, the number of particles and the particle volume ratio in sequentially dispensed droplets were measured. Hydrophilic and hydrophobic surfaces were tested to find a suitable surface for counting the number of particle. It was confirmed that the dispensed particles concentrated into the center of the droplet on the smooth CD surface after evaporation of liquid. As the applied positive pressure increased, the number of particles per droplet increased consistently and the volume fraction of particles remained constant.

The guillotined cutting process for the pipe was studied in this paper. Until now guillotining mechanism can not be practically applied in the industries because of the deformation of sheared section around cutting area, the coarse sheared surface, and the burs. To find optimum shapes of blade, several types of blade were experimentally studied. The cutting force normal to the axial direction of the pipe was compared with the theoretical result based on the cutting energy. The experimental maximum cutting forces were very good agreement with the theoretical results. It also discussed that the design parameters of guillotining system such as the blade shape and the clearance between the blade and the die made effects to the deformation of the cutting cross section area. The results show that the guillotining method can be applicable to the pipe cutting system by optimizing the blade shape and the clearance between the blade and the die of the guillotined cutting system with respect to the sheared pipe material.