Numerical simulation of electroosmotic flow in hydrophobic microchannels

Electroosmotic flow (EOF) is a promising way for driving and mixing fluids in microfluidics. For the parallel-plate microchannel with the hydrophobic surface, this paper solved the governing equations using the finite element method (FEM), and the effects of microchannel height, electric strength and ionic concentration on EOF were thus investigated. The simulation indicates that the transient characteristics of EOF are similar in hydrophobic and hydrophilic microchannels, the steady time of EOF is proportional to the square of microchannel height, and the scale is microsecond. EOF velocity is proportional to the electric strength and independent of the channel height, and decreases slowly with the ionic concentration, which is lower than that in hydrophilic microchannel due to the presence of slip length in hydrophobic microchannel. The results can provide valuable insights into the optimal design of microchannel surfaces to achieve accurate EOF control in hydrophobic microchannel. Supported by the National Natural Science Foundation of China (Grant No. 50730007)     

Research on polyfluorene derivatives end-capped by N-hexyl-carbazole and benzene

Copolymers of 9,9-dioctylfluorene (DOF) and 2-thienyl-benzothiadiazole (DBT) were synthesized by Suzuki reaction and end-capped by N-hexyl-carbazole and benzene, which were abbreviated as PDOF-DBT-Cz and PDOF-DBT-B, respectively. The photophysical, electrochemical and thermal properties of the copolymers were studied. The results indicated that replacement of N-hexyl-carbazole as end-capping group of PDOF-DBT can vary light color and improve luminescence efficiency. Supported by the Major Project of Science Foundation Ministry of Education of China (Grant No. 207015) and the National Natural Science Foundation of China (Grant No. 20671068)     

Ultralight X-type lattice sandwich structure (I): Concept,fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060,10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

Study on hydrogen atom adsorption and diffusion properties on Mg (0001) surface

Hydrogen atom adsorption and diffusion properties on clean and vacancy defective Mg (0001) surface have been investigated systematically by using a first-principles calculations method based on the density functional theory. The calculation results of adsorption energy and diffusion energy barrier show that hydrogen atom is apt to be adsorbed at fcc and hcp sites on clean Mg (0001) surface, and fcc adsorption site is found to be more preferred. The highest diffusion energy barrier is estimated as 0.6784 eV for the diffusion of hydrogen from clean Mg (0001) surface into its bulk. Surface effects, which affect hydrogen diffusion obviously, results in a slow diffusion velocity of hydrogen from surface to subsurface, while a fast one from subsurface to bulk, indicating the range of surface effects is only restricted within two topmost layers of Mg (0001) surface. Comparatively, Mg atom vacancy on Mg (0001) surface not only enhances the chemisorption interaction between H and Mg surface, but also benefits H atom diffusion in Mg bulk with relatively more diffusion paths compared with that of clean surface. Besides, hydrogen atom is found to occupy mostly the tetrahedral interstice when it diffuses into the Mg bulk. Further analysis of the density of states (DOS) shows that the system for hydrogen atom to be adsorbed at fcc site has a lower DOS value (N (E _F)) at Fermi level and more bonding electrons at the energy range blow the Fermi level of H/Mg (0001) system as compared with that at hcp site. On the other hand, the enhanced chemisorption interaction between hydrogen and defective surface should be attributed to the fact that the electronic structures of Mg (0001) surface are modified by an Mg vacancy, and the bonding electrons of the topmost layer Mg atoms are transferred from low energy range to Fermi level, which is in favor of improving the surface activity of Mg (0001) surface. Supported by the PhD Programs Foundation of Ministry of Education of China (Grant No. 200805321032), the Science and Technology Program Project of Hunan Province (Grant No. 2008GK3083) and the Program for Changjiang Scholars and the Innovative Research Team in university (Grant No. 531105050037)     

Optical property of amorphous semiconductor mercury cadmium telluride from first-principles study

The structural and optical properties of amorphous semiconductor mercury cadmium telluride (a-MCT) are obtained by the first principles calculations. The total pair distribution functions and the density of states show that the a-MCT has the semiconductor characteristic. The calculated results of dielectric function show that E ₂ peak of the imaginary of dielectric function for the crystal mercury cadmium telluride abruptly disappears in the amorphous case due to the long-range disorders. And the imaginary of dielectric function of a-MCT shows a large broad peak, which is in agreement with the available results of other amorphous semiconductors. From the linear extrapolation of the curve ħωɛ ₂(ω)^1/2 versus ħω, it can be obtained that the optical energy gap of amorphous semiconductor Hg_0.5Cd_0.5Te is 0.51±0.05 eV. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2007CB613205), the National Natural Science Foundation of China (Grant Nos.10725418, 10734090, 60576068), the Key Fund of Shanghai Science and Technology Foundation (Grant No. 08JC1421100) and the Knowledge Innovation Program of the Chinese Academy of Sciences     

Separation of nanocolloids driven by dielectrophoresis: A molecular dynamics simulation

The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis (DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive potential energy, which accorded with the DLVO theory. Supported by the National Hi-Tech Research and Derelopment Program of China (“863” Project) (Grant No. 2006AA04Z351) and the National Natural Science Foundation of China (Grant Nos. 50675033, 30770553)     

Effect of coagulation temperature on structures and properties of poly(<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) (DHPBO) fibers during dry-jet wet-spinning process

The effect of coagulation temperature on the morphology, microstructures and mechanical properties of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) fibers was investigated during dry-jet wet-spinning process, in which the coagulation bath concentration and drawn ratio were kept as 10 wt% of PPA in water and 1.7, respectively. The structures and mechanical properties of the as-spun DHPBO fibers were characterized by FTIR, XRD, SEM, and single fiber tensile testing. The results indicated that in PPA/H₂O coagulation system, when the coagulation temperature was 25°C, highly crystallized DHPBO as-spun fibers possessing fine crystallites, circular and smooth morphology, and excellent mechanical properties could be achieved. Supported by the National Natural Science Foundation of China (Grant No. 50673017), Shanghai Leading Academic Discipline Project (Grant No. B603) and the Program of Introducing Taleuts of Discipline to University of People’s Republic of China (“111” Program) (Grant No. 111-2-04)     

Development of a unified viscoplasticity constitutive model based on classical plasticity theory

The traditional unified viscoplasticity constitutive model can be only applied to metal materials. The study of the unified constitutive theory for metal materials has discovered the correlation between the classical plasticity theory and the unified viscoplasticity constitutive model, thus leading to the concepts of the classic plastic potential and yield surface in the unified constitutive model. Moreover, this research has given the continuous expression of the classical plastic multiplier and presented the corresponding constructive method, which extends its physical significance and lays down a good foundation for the application of the unified constitutive theory to the material analysis in more fields. This paper also introduces the unified constitutive model for metal materials and geo-materials. The numerical simulation indicates that the construction should be both reasonable and practical. Supported by the National Natural Science Foundation of China (Grant No. 90410012)     

Rapid prediction method for nonlinear expansion process of medical vascular stent

A neural network model with high nonlinear recognition capability was constructed to describe the relationship between the deformation impact factors and the deformation results of vascular stent.Then,using the weighted correction method with the attached momentum term,the network training algorithm was optimized by introducing learning factor η and momentum factor ψ,so the speed of the network training and the system robustness were enhanced.The network was trained by some practi-cal cases,and the statisti...     

A new type counter electrode for dye-sensitized solar cells

A new type counter electrode for dye-sensitized solar cells (DSCs) was proposed which consists of substrate, aluminum film and platinum film. The new type counter electrode can obviously improve the photoelectric conversion efficiency of DSCs from 3.46% to 7.07% under the standard AM1.5 irradiation condition. Advantages and shortcomings of this new type counter electrode in terms of electrical properties, optical properties and anti-corrosive properties were analyzed. As a result, some improvements were proposed. Supported by the Key Foundation for Fundamental Research of Tianjin Municipal Science & Technology Commission in China ( Grant No. 06YFJZJC01700) and the National Basic Research Program of China (“973“ Project) (Grant Nos. 2006CB20260, 2006CB202603)