By embedding “dilute” gold nanoparticles in single polystyrene thin films as “markers”, we probe the local viscosity of the free surface at temperatures far above the glass transition temperature (Tg). The techniq...
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By embedding “dilute” gold nanoparticles in single polystyrene thin films as “markers”, we probe the local viscosity of the free surface at temperatures far above the glass transition temperature (Tg). The technique used was x-ray photon correlation spectroscopy with resonance-enhanced x-ray scattering. The results clearly showed the surface viscosity is about 30% lower than the rest of the film. We found that this reduction is strongly associated with chain entanglements at the free surface rather than the reduction in Tg.
The commercialization of proton exchange membrane (PEM) fuel cells depends largely upon the development of PEMs whose properties are enhanced over current perfluorinated sulfonic acid PEMs. Understanding how a PEM'...
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作者：
张广照Department of Chemical Physics
Department of Polymer Science and Engineering The University of Science and Technology of China
The effects of the chain length, active end group and concentration on the association of living polystyryllithium (PS(-)Li(+)) chains in benzene were examined by a combination of static and dynamic laser light scatte...
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The effects of the chain length, active end group and concentration on the association of living polystyryllithium (PS(-)Li(+)) chains in benzene were examined by a combination of static and dynamic laser light scattering in a cuvette equipped with a high-vacuum stopcock. The results show that long PS(-)Li(+) chains (M(w) > 1 x 10(4)) usually form dimers in the solution. In contrast, shorter PS(-)Li(+) chains exhibit two relaxation modes, where the fast mode is related to the translational diffusion of the living chain dimers. The end capping of the living chain with bulky 1,1-diphenylethene (DPE) leads to an intensity increase of the slow mode, indicating that the slow mode is not due to the chain aggregates but to temporal aggregates or long-range density fluctuation induced by weak electrostatic dipole-dipole interaction between ionic pairs at the chain ends.
This article aims to illustrate an application of the Taguchi method of experimental design (TMED) for the preparation of poly(lactic acid) (PLA) nanoparticles via a nanoprecipitation technique. The effect of four per...
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Zirconia coated carbonyl iron particle-based magnetorheological fluid was developed for magnetorheological finishing. Particles were coated via sol-gel synthesis. Spot polishing tests were performed over 3 weeks with ...
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This article briefly overviews the pros and cons of pretreatment systems for bioenergy production relative to the use of green liquor (GL) pretreatment method to enhance saccharification. Quantitative analyses of gluc...
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This article briefly overviews the pros and cons of pretreatment systems for bioenergy production relative to the use of green liquor (GL) pretreatment method to enhance saccharification. Quantitative analyses of glucose yield from hardwood chips pretreated using GL as a function of different parameters is discussed. The influence of pretreatment conditions, such as alkalinity and sulfidity charge, were studied to analyze their influence on the glucan yield. The results suggest that higher alkalinity and sulfidity promote an increase in delignification in the cellulose matrix and facilitate enzymatic hydrolysis. The results also indicate that higher enzyme activity correlated well to higher glucan yield.
In common with many other structured fluids, block copolymers can be effectively oriented by shear. This susceptibility to shear alignment has previously been shown to hold even in thin films, containing as few as two...
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In common with many other structured fluids, block copolymers can be effectively oriented by shear. This susceptibility to shear alignment has previously been shown to hold even in thin films, containing as few as two layers of spherical microdomains, or even a single layer of cylindrical microdomains. A phenomenological model has been proposed [M. W. Wu, R. A. Register, and P. M. Chaikin, Phys. Rev. E 74, 040801(R) (2006)] to describe the alignment of such block-copolymer films, yielding the microdomain lattice order parameter as a function of shearing temperature, stress, and time. Here we directly test the central idea of that model, that the grains which are most misaligned with the shear direction are selectively destroyed, to reform in a direction more closely aligned with the shear. Films are first shear aligned from a polygrain state into a monodomain orientation and are then subjected to a second shear, at a variable stress (σ) and misorientation angle (δθ) relative to the monodomain director, allowing the effects of σ and δθ to be independently and systematically probed. For both cylinder-forming and sphere-forming block copolymers, these experiments confirm the basic premise of the model, as the stress required for realignment increases monotonically as δθ becomes smaller. For a cylinder-forming block copolymer, we find that the characteristic stress σc required to realign cylinders from one monodomain orientation to another is indistinguishable from that required to generate a monodomain orientation from the polygrain state. By contrast, the hexagonal lattice of spheres requires a value of σc more than 3 times as high for reorientation than for generation of the initial monodomain orientation.
Alumina nanofibers containing either platinum or rhodium crystalline nanoparticles have been successfully fabricated by electrospinning a solution of polyvinylpyrrolidone mixed with platinum or rhodium chloride and su...
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