Hiromasa Yagyu

Micropowder blasting with nanoparticles dispersed polymer mask for rapid prototyping of glass chip

We present a new rapid prototyping technique without a photolithography step to produce a glass chip with high aspect ratio channel for a micro total analysis system (µTAS). This technique consists of a powder blasting technique and direct laser patterning of Au nanoparticles dispersed polymer mask technique, and is useful in the development stage of a glass chip. The mask thickness and powder blasting condition were optimized for the fabrication of a glass chip with a higher aspect ratio channel. Under the optimized processing condition, the microchannel with a maximum aspect ratio of 2.1 in a glass substrate was successfully realized. The proposed technique was applied to a glass chip for electrophoresis and its performance for DNA separation analysis was confirmed.

Application of nanoparticles dispersed polymer to micropowder blasting mask

Improvements in micropowder blasting have been realized for rapid prototyping of channels in glass substrates. The technique presented in this study consists of laser patterning of Au nanoparticles dispersed polymer and micropowder blasting. The patterned polymer was utilized as a mask material for the subsequent mechanical removal of the glass by the micropowder blasting. Five different polymers were tested for the matrix material. Using a line and space mask pattern of 110 /spl mu/m in width, fabricated channels were created in the glass with a maximum aspect ratio of 2.1. The validity of the micropowder blasting using Au nanoparticles dispersed polymer mask was confirmed; additionally, we demonstrated that the micropowder blasting technique with elevated polymer mask temperature was able to reduce erosion of the polymer mask.

Coarse-grained Molecular Dynamics Simulation of the Effects of Strain Rate on Tensile Stress of Cross-Linked Rubber

A cross-linked rubber model with different cross-linking densities was created using the bead-spring model, and a uniaxial elongation simulation was conducted to evaluate the strain rate dependence of tensile stress. To evaluate the effect, the relaxation rate, which is calculated from Rouse relaxation time using the uncross-linked linear polymer model with different numbers of beads, was compared with the strain rate of a rubbery state, indicated by the flat region in the stress–strain rate curve. Moreover, by comparing the stress–strain curve of the models and that of cross-linked chloroprene rubber in an experiment, the reduced unit of the model was converted to realistic units. Thus, it was confirmed that the model can be used to simulate elongation behavior using standard elongation speed. From the uniaxial elongation simulation results of the cross-linked rubber model, it was found that the variation of stress at a small strain rate affected the number of cross-links, which contributed to the relaxation rate of the molecules between cross-links.

Three-dimensional simulation of powder blasting with a polymer mask using a cellular automaton

A three-dimensional (3D) simulation for micropowder blasting was carried out for the first time to predict the convex corner structure of a processed glass substrate with patterned mask erosion. The simulator utilized a cellular automaton algorithm which consisted of combinations of two orthogonal planes of two-dimensional (2D) cells and a solid particle erosion model. It was confirmed that the effect of erosion at the convex corner of the mask on the glass processing profile, which cannot be predicted in the previous 2D simulation, was successfully simulated using our 3D simulator.

Laser microfabrication using nano-particles dispersed polymer resist

A new laser microfabrication technique to realize a high aspect ratio microstructure with free shaped wall using newly developed resist was proposed. The resist is made of ethylcellulose in which nano-particles with average diameter of 3.4 nm was dispersed. Since this resist has a strong absorption at wavelength of about 530 nm, it can be processed using focused low power output Nd:YVO/sub 4/-SHG laser. From the experiments, it was confirmed that the cross-sectional shape of processed resist microstructure can be controlled by the gold (Au) concentration (1-50 wt%) and the laser beam power. The processed depth showed a strong dependency on Au concentration and showed maximum at 17 wt% Au concentration. From analysis of the processed resist surface, it was revealed that the Au aggregation at the bottom of the processed channel played an important role for the resultant processed depth.

Negative-photoresist mechanical property for nano-filtration membrane embedded in microfluidics

We report on a simple UV photolithography based fabrication for an epoxy-based filtration membrane and its primary features such as the permeability and the elastic modulus toward a design of polymer-based microfluidic systems. The elastic modulus of filtration membrane was measured by an indentation test, and then which was evaluated by a cross-linked ratio of epoxy group to clarify the dependence on the process parameters. It was revealed for the first time that the elastic modulus for filtration membrane varied from 3.8 GPa to 4.9 GPa according to the cross-linked ratio of 0.5 to 0.75.

Particle size dependence of the laser microfabrication of gold nanoparticles dispersed in polymer resists

A laser microfabrication technique for a polymer film based on the absorbance of Au nanoparticles for realizing a nano-microstructure was proposed. The polymer films were made of ethylcellulose wherein Au nanoparticles were dispersed. Since the absorption spectrum, which influences laser processing ability, depends on the size of the Au nanoparticles in the polymer, four sizes of Au nanoparticles were prepared using a liquid-phase reduction method and a newly developed size control technique. The polymer films with Au nanoparticles of different sizes were processed using a Nd:YVO4-SHG laser. The results confirmed that the laser processing ability was unrelated to the absorption coefficient of the polymer film but the increase of the processed depth can be explained by the decrease of full width at half maximum of the absorption peak, indicated by the sharpness of the peak.

Simulations of the effects of filler aggregation and filler-rubber bond on the elongation behavior of filled cross-linked rubber by coarse-grained molecular dynamics

ABSTRACT The effects of aggregation of filler and filler-rubber bond on the elongation behavior of filled cross-linked rubber were studied using coarse-grained molecular dynamics. Models with aggregated and dispersed fillers were applied for elongation simulations. The results confirmed that the aggregation of fillers conduced to large stress at small strain values and resulted in a large bond stress. In addition, an increase in the number of filler-rubber bonds affected the elongation stress in the large strain region. Furthermore, the simulations of the elongation behaviors of the models with different numbers of filler-rubber bonds confirmed that the stress in the large strain region increased with the elongation of the bonds of the polymer chain between the fillers.

Coarse-Grained Molecular Dynamics Model of Double-Stranded DNA for DNA Nanostructure Design

A new coarse-grained molecular dynamics double-stranded DNA model (nCG-dsDNA model) using an improved beads-spring model was proposed. In this model, nucleotide comprising phosphate, sugar, and base group were replaced by a single bead. The double stranded model with 202 base pairs was created to tune the parameters of the bond, the nonbond, stack, angle bending, and electrostatic interaction. The average twisted angle and the persistence length of the model without electrostatic interaction were calculated at 35.3° and 120.3 bp, confirming that the proposed model successfully realized the experimentally observed double-stranded DNA structure. Moreover, the model with electrostatic interaction was discussed. From calculation results, we confirmed that the dependency of the salt concentration on the persistence length of the nCG-dsDNA model at the 30% charge is in good agreement with the Poisson-Boltzmann theoretical model.

New coarse-grained molecular dynamics model of double stranded DNA chain for DNA origami

New coarse-grained molecular dynamics model of double stranded DNA (nCG-dsDNA model) was reported. The nCG-dsDNA model was made by newly developed simple bead-spring model for realizing a helix structure. The phosphate group, sugar group, and base group in an actual double stranded DNA chain were represented by a single bead. The nCG-dsDNA model with 202 base pair was utilized to tune the bond potential between connected two beads of a chain, the nonbond potential between stack sites and the angle bending potential between three beads. The twisted angle of each chains in the model was calculated as 35.3 degree. From this result, it was confirmed that the actual double stranded DNA structure was well realized by the proposed model. Moreover, it was confirmed that a persistence length of the nCG-dsDNA model was in good agreement with the results of conventional DNA model (oxDNA model) and experiments.