Yu Min Yang
National Cheng Kung University
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Featured researches published by Yu Min Yang.
Applied Physics Letters | 2007
Sheng Chih Lin; Yuh-Lang Lee; Chi Hsiu Chang; Yu Jen Shen; Yu Min Yang
Two methods, coupling self-assembled monolayer and chemical bath deposition (CBD), were utilized to assemble cadmium sulfide (CdS) quantum dots (QDs) onto mesoporous TiO2 films for dye-sensitized solar cell (DSSC) applications. Colloidal CdS QDs were first self-assembled on the TiO2 surface. CBD was then introduced to replenish the incorporated amount and increase the coverage ratio of CdS QDs on the TiO2 surface. The preassembled CdS QDs act as nucleation sites in the CBD process, forming a CdS nanofilm with an interfacial structure capable of inhibiting the recombination of injected electrons. An efficiency as high as 1.35% for the QD-sensitized DSSC was achieved using the present strategy.
Journal of Microencapsulation | 2006
L.-Y. Wang; Ping Szu Tsai; Yu Min Yang
Spherical silica microcapsules containing phase-change material (PCM) were prepared by the sol-gel method in O/W emulsion. This is the first time that inorganic encapsulation of PCM with core/shell structure has been studied. The results of this synthesis revealed that micron size (4 ∼ 8 µm) silica microspheres encapsulating n-pentadecane can be successfully created from acidic solutions ([H+] ≥ 1.44 N) by using cationic surfactants as the emulsifiers. The identification of the mechanisms for the formation of silica shell at the oil–water interface indicates that it should be the charge-controlled mechanism through S+X−I+ (positively charged surfactant-halide ion-positively charged silica species) electrostatic interactions or the reaction rates-controlled mechanism working on cationic emulsifiers.
Journal of Microencapsulation | 2005
Y.-H. Tseng; M.-H. Fang; Ping Szu Tsai; Yu Min Yang
Microcapsules for energy storage and/or heat transfer applications containing phase-change materials (PCMs—including n-pentadecane, n-eicosane and a paraffin wax) were successfully produced by emulsifying the PCMs as small droplets in an aqueous, water-soluble urea-formaldehyde pre-polymer solution substantially free of emulsifier while polymerizing the pre-polymer at the interface by acid-catalyst. The core/shell structured microcapsules were also characterized with size distribution analysis, scanning electron microscopy, FTIR spectrometry and differential scanning calorimetry.
Journal of Heat Transfer-transactions of The Asme | 1990
Ying Liang Tzan; Yu Min Yang
In the first part of this work, nucleate boiling of aqueous solutions of sodium lauryl sulfate (SLS) over relatively wide ranges of concentration and heat flux was carried out in a pool boiling apparatus. The experimental results show that a small amount of surface active additive makes the nucleate boiling heat transfer coefficient h considerably higher, and that there is an optimum additive concentration for higher heat fluxes. Beyond this optimum point, further increase in additive concentration makes h lower. In the second part of this work, nucleate boiling heat transfer rate for n-propanol-water binary mixtures with various amounts of sodium lauryl sulfate were measured in the same pool boiling apparatus. The importance of the mass diffusion effect, which is caused by preferential evaporation of the more volatile component at the vapor-liquid interface on the boiling of the binary mixture, has been confirmed. However, it is shown that the effect exerted by the addition of a surfactant dominates over the mass diffusion effect in dilute binary mixtures.
Physical Chemistry Chemical Physics | 2013
Ching Lun Chen; Ting Wei Chang; Hsisheng Teng; Chun Guey Wu; Chia-Yuan Chen; Yu Min Yang; Yuh Lang Lee
Poly(acrylonitrile-co-vinyl acetate) (PAN-VA) is utilized as a gelation agent to prepare gel-state electrolytes for dye-sensitized solar cell (DSSC) applications. Based on the synergistic effect of PAN-VA and TiO(2) fillers in the electrolyte, the gel-state DSSC can achieve a conversion efficiency higher than that of a liquid counterpart. The high performance of the gel-electrolyte is attributed to the in situ gelation property of the gel-electrolyte, the contribution of the PAN-VA to the charge transfer, as well as the enhancement effect of TiO(2) fillers on the charge transfer at the Pt-electrolyte interface. The experimental results show that the efficiencies of the gel-state cells have little dependence on the conductivity of the electrolytes with various contents of PAN-VA, but are closely related to the penetration situation of the electrolyte in the TiO(2) film. For PAN-VA concentrations ≤15 wt%, the electrolyte can be easily injected at room temperature based on its in situ gelation property. For higher PAN-VA concentrations, good penetration of the high viscous electrolyte can be achieved by elevating the operation temperature. By utilizing a heteroleptic ruthenium dye (coded CYC-B11), gel-state DSSCs with an efficiency of above 10% are obtained. Acceleration tests show that the cell is stable under one-sun illumination at 60 °C.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | 2000
Chin-Ming Chen; Chun-Hsiung Lu; Chien Hsiang Chang; Yu Min Yang; Jer-Ru Maa
Abstract A laboratory study was conducted to evaluate the effect of pH on the stability of oil-in-water emulsions stabilized by a commercial splittable surfactant Triton SP-190 by comparison with the results obtained by a common surfactant Triton X-100. The emulsion stability was explored by measuring the volume of oil phase separated and the size of the dispersed droplets. It was found that the addition of inorganic acids did not significantly affect the stability of emulsions stabilized by Triton X-100, but had a profound influence on the stability of emulsions stabilized by Triton SP-190. Moreover, the droplet size of a Triton X-100-stabilized emulsion and its dynamic interfacial activity were insensitive to acids. However, at lower pH the droplet size of the emulsions stabilized by Triton SP-190 was considerably increased. From the dynamic interfacial tension measurements the dynamic interfacial activity of Triton SP-190 at the oil/water interface was found to be strongly inhibited by the addition of acids, resulting in a slower decreasing rate of dynamic interfacial tension. The results demonstrate that the dramatic destabilization of Triton SP-190-stabilized emulsions could be realized by the use of acids, which evidently changed the interfacial properties of the surfactant and resulted in a higher coalescence rate of oil droplets.
Journal of Colloid and Interface Science | 1984
Yu Min Yang; Jer Ru Maa
Abstract In order to understand the behaviors of the stretching gas-liquid interface and the effects of surfactants, the coalescence of nitrogen bubble pairs issued from neighboring nozzles submerged in water has been studied by means of high-speed photography. It is shown that small amount of surface active additive is able to increase the coalescence time greatly. The transition from 0 to 100 percent bubble coalescence during their stay at the nozzle mouths happens over a very narrow concentration range. The central value of this concentration range increases with the increase of bubbling frequency, which is proportional to the heat flux in the case of nucleate boiling.
Experimental Thermal and Fluid Science | 1998
Wuu-Tsann Wu; Yu Min Yang; Jer-Ru Maa
Abstract While certain surfactant additives are well known to significantly enhance boiling heat transfer, the enhancement mechanism is still not so clear for the present. In order that more conclusive information of fundamental boiling phenomena in surfactant solutions can be collected, surfactant effects on interfacial properties at gas/liquid interface, nucleate boiling heat transfer, boiling incipience, and single vapor bubble growth dynamics for three additives – including 99% SDS, 95% SDS, and Triton X-100 – were experimentally studied in this work. The nucleate boiling heat transfer coefficients were tried to correlate with the equilibrium and dynamic surface tension of the aqueous surfactant solutions. The results reveal that neither equilibrium nor dynamic surface tension can successfully explain the boiling phenomena. On the other hand, different appearance of boiling above the heater surface suggests that different heat transfer mechanism may prevail in surfactant solutions. A correlation between the nucleate boiling heat transfer coefficient enhancement and the vapor bubble occupied area increase was satisfactorily obtained. The micro-wedge model considering the evaporation at the interface of the bubble base and the mass flow in the wedge between the interface and the heated wall due to capillary forces may then be assumed for heat transfer processes in surfactant solutions. Surfactant effect on boiling incipience at a target cavity was also examined. The results show that surface tension only cannot determine boiling incipience in surfactant solutions in general. The variations in individual behavior of the successive vapor bubbles from even the same cavity, however, seems to overwhelm the effect of surfactant on single vapor bubble growth dynamics. No convincing conclusion can be drawn for bubbling periods and departure diameter.
Sensors and Actuators B-chemical | 2003
Yuh-Lang Lee; Chuan Yi Hsiao; Chien Hsiang Chang; Yu Min Yang
Abstract Copper phthalocyanine (CuPc) and copper tetra-tert-butyl phthalocyanine (CuTTBPc) were vacuum deposited onto alumina substrates. The surface morphology and crystalline structures of the films prepared by the two compounds were studied first. These films were then used for the experiments of NO2 sensing. The effects of gas sensing temperature, as well as the NO2 concentration, on the sensing properties were studied for both films. The experimental results show that both CuPc and CuTTBPc films exhibit fine-grain morphology and low crystallinity. Due to the tetra-tert-butyl (ttb) substitution on the periphery of phthalocyanine, CuTTBPc film has a larger lattice spacing, higher film resistance, and a higher recovery ratio in the NO2 sensing experiments. On the contrary, the response rate and sensitivity of a CuPc film are superior to that of a CuTTBPc film. By varying the sensing temperature, it was found that the elevation of sensing temperature can improve the sensing response, recovery ratio, and sensitivity of the sensing films. At high concentrations of NO2, a longer response time is required and the recovery ratio becomes smaller. In addition, the disadvantage caused by the elevation of NO2 concentration can also be improved by using an elevated sensing temperature.
Chemical Engineering Research & Design | 2001
Yu Min Yang; Jer-Ru Maa
By testing against collected data from twelve surfactant additives, criteria for a given surfactant as a competent additive in enhancing nucleate boiling heat transfer of water is proposed in this work. As a result of the criteria, high solubility, high equilibrium surface tension depression, and low equilibrium contact angle depression are required. A surfactant is incapable of enhancing boiling of water, in which it dissolves sparsely. For a highly soluble surfactant, boiling heat transfer enhancement by its addition is enhanced by the depression of equilibrium surface tension but suppressed by the depression of equilibrium contact angle. These two effects counterbalance each other and result in different degrees of boiling enhancement. Surfactant additives can be categorized accordingly.