Crown behavior and bubble entrainment during a drop impact on a liquid film

Physical and mathematical models are established to simulate a single liquid drop impinging onto a liquid film using the coupled level set and volume of fluid method. The crown liquid sheet after impact is obtained, which coincides well with the experimental results in literatures. Influence of Weber number, Reynolds number and the dimensionless film thickness on the crown diameter and height is discussed quantitatively. Results indicate that the crown diameter is independent of the two non-dimensional numbers, while it can be increased by reducing the dimensionless film thickness. The crown height increases with the increasing of Weber number, but Reynolds number has small effect on it. Mechanism of the jet formation process is revealed by analyzing pressure distribution and velocity field in the liquid. It is found that both pressure difference in the neck region and velocity discontinuity can greatly affect the jet formation. Besides, the bubble entrainment phenomenon during a liquid drop impact on a liquid film is successfully captured with this numerical method. It is found that the increase in both impact Weber number and the drop diameter contributes to the emerging of bubble rings.     

Heparin-like macromolecules for the modification of anticoagulant biomaterials

A heparin‐like structured macromolecule (HLSM) is synthesized by RAFT polymerization using carboxyl‐terminated trithiocarbonate as the RAFT agent. The HLSM can be directly blended with PES in DMAC to prepare flat‐sheet membrane by means of a liquid–liquid phase separation technique. The synthesized polymeric material retard blood clotting and the modified membrane exhibits good anticoagulant ability due to the existence of the important functional groups ? SO₃H, ? COOH and ? OH. The anionic groups on the membrane surface may bind coagulation factors and thus improve anticoagulant ability. The results indicate that the HLSM has potential to improve the anticoagulant properties of biomaterials and to be applied in blood purification including hemodialysis and bioartificial liver supports.

     

Comparison of surface segregation and anticoagulant property in block copolymer blended evaporation and phase inversion membranes

In our recent study, an ABA amphiphilic triblock copolymer poly(vinyl pyrrolidone)‐b‐poly(methyl methacrylate)‐b‐poly(vinyl pyrrolidone) (PVP‐b‐PMMA‐b‐PVP) was synthesized and directly blended with polyethersulfone (PES) to prepare membranes. To further investigate the effects of surface energy and miscibility on the near‐surface composition profile of the membranes, evaporation membrane and phase inversion membrane of PES/PVP‐b‐PMMA‐b‐PVP were prepared by evaporating the solvent in a vacuum oven, and by a liquid–liquid phase separation technique, respectively. The surface composition and morphology of the membranes were investigated using XPS and tapping mode atomic force microscopy, and the surface segregations of the membranes were compared and discussed. For the evaporation membrane, PVP blocks were buried below the lower surface energy PMMA blocks and PES substrate at the airside surface. For the phase inversion membrane, however, the hydrophilicity of PVP blocks were the biggest driving force because of the high speed exchange between water and solvent, and present at the membrane surface. Thus, the modified PES membrane prepared by using phase inversion method has a layer of PVP block brushes on its surface and has the better anticoagulant property, which might improve the blood compatibility of the membrane and has potential to be used in blood purification. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanical behavior of a pH-sensitive hydrogel ring used in a micro-optical device

A hydrogel is a polymer network that can absorb a large quantity of solvent and swell due to a physical or chemical stimulus. Hydrogels are more and more used as smart materials in recent micro-applications. This fact requires the development of adequate models and simulation tools for their large deformation behavior. These models must also predict the onset of instabilities, such as folding or creasing. In this work, we study an interesting application of adaptive optical microsystem using a previously developed theory of inhomogeneous large deformation of a pH-sensitive hydrogel. The devices function is based on the swelling of a ring made of a pH-sensitive hydrogel. The latter controls the focal length of the liquid microlens. Our aim is to analyze major design parameters that affect the hydrogel ring behavior and the function of the micro-optical device. The problem is solved numerically with the finite element commercial software ABAQUS. Various modes of large deformation and the influence of the rings aspect ratio on the behavior of the micro-device are investigated. Results show that, for relatively short rings, a stable swelling takes place. Rings with a relatively big aspect ratio can have an unstable swelling with the propagation of a creasing instability. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Resonant behavior of a membrane of a dielectric elastomer

This paper analyzes a membrane of a dielectric elastomer, prestretched and mounted on a rigid circular ring, and then inflated by a combination of pressure and voltage. Equations of motion are derived from a nonlinear field theory, and used to analyze several experimental conditions. When the pressure and voltage are static, the membrane may attain a state of equilibrium, around which the membrane can oscillate. The natural frequencies can be tuned by varying the prestretch, pressure, or voltage. A sinusoidal pressure or voltage may excite superharmonic, harmonic, and subharmonic resonance. Several modes of oscillation predicted by the model have not been reported experimentally, possibly because these modes have small deflections, despite large stretches.     

Toughening of poly(lactide acid) with low crystallinity through biaxial poststretching

Poly(lactide acid) (PLA) is an eco-friendly, biocompatible and biodegradable polymer that has been extensively explored in diverse applications ranging from biomedical devices to food packages. One well-known limitation of PLA in the applications is its low mechanical toughness and small stretchability. In this work, we have conducted systematic studies of the effects of the thermo-mechanical processing on the mechanical behaviors of PLA with extremely low crystallinity (less than 3%). It is found that a freshly quenched PLA after hot pressing can be quite stretchable and tough. However, after only 2 days of aging at room temperature, the PLA becomes very brittle. We attribute such aging-induced ductile-to-brittle transition of the PLA to its plastic deformation mode changing from shearing to crazing. To increase the toughness and stability of the PLA, we apply poststretching onto the PLA. Our results have shown that after poststretching, both the toughness and stretchability of aged PLA can be greatly increased. Moreover, the mechanical properties of the PLA after poststretching become more aging resistant.     

Research on La–Co-substituted strontium ferrite magnets for high intrinsic coercive force

M-type strontium ferrites with substitution of Sr²⁺ by rare-earth La³⁺, and a little amount of Fe³⁺ by Co²⁺ according to the formula Sr_1−xLa_xFe_12−xCo_xO₁₉, are prepared by the ceramic process. Effects of the substituted amount of La³⁺ and Co²⁺ on structure and magnetic properties of Sr_1−xLa_xFe_12−xCo_xO₁₉ compounds have systematically been investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and B–H hysteresis curve measurements. In our results, the suitable amount of La³⁺–Co²⁺ substitution may remarkably increase saturation magnetization. Intrinsic coercive force (H_cj) of Sr ferrite magnets is evidently increased without significant decrease in residual flux density (B_r) by La³⁺–Co²⁺ substitution.     

冠醚与碱金属苦味酸盐在氯仿中形成络合物的电导

测定了氯仿中碱金属苦味酸盐——冠醚络合物的电导率及络合比。确定了体系中电导率、冠醚浓度和络合比之间的关系。讨论了这些结果的某些应用。     

Effects of nano-TiO2 dispersion on the thermoelectric properties offilled-skutterudite Ba0.22Co4Sb12

Homogeneously dispersed nano-TiO₂ was introduced into the matrix of n-type barium-filled cobalt antimony (Ba_0.22Co₄Sb₁₂) via sol–gel method successfully. The Seebeck coefficients are improved and the lattice thermal conductivities are depressed with a proper addition of nano-TiO₂ not more than 0.8 vol.%, while the electrical conductivities nearly remain unchanged. The effects of n-type semiconductive nanoscale inclusions on the electrical and thermal transport characteristics are discussed. Microstructure analyses indicate that the fine nanoinclusions locate on the grain boundaries as well as inside grains, which serve as extra phonon scattering mode and new type energy filtering. As a result, the optimal ZT value was achieved for the sample of 0.4 vol.% TiO₂ composition.