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91.
Associating polymers are hydrophilic long-chain molecules containing a small amount of hydrophobic groups. The aqueous solutions
show viscoelastic responses above some critical concentrations because a three-dimensional structure is formed by association
of hydrophobic groups. When the associating polymers are added to silica suspensions at low concentrations, the flocculation
is induced by bridging mechanisms, and the flow of suspensions become shear-thinning. For suspensions prepared with polymer
solutions in which the associating network is developed, the viscosity decreases, shows a minimum, and then increases with
increasing particle concentration. The viscosity decrease may arise from the breakdown of associating network due to adsorption
of polymer chains onto the silica surfaces. As the particle concentration is increased, the polymer concentration in solution
is decreased, and finally, all polymer chains are adsorbed on the surfaces. Beyond this point, the partial coverage of particle
surfaces takes place and strong interactions are generated between particles by polymer bridging. Since the stable suspensions
are converted to highly flocculated systems, the viscosity is increased and the flow becomes shear-thinning. The concentration
effect of silica particles on the viscosity behavior of suspensions can be explained by a combination of viscosity decrease
in solution due to polymer adsorption and viscosity increase due to flocculation. 相似文献
92.
A concept demonstration has been made to simultaneously enhance both O2 and CO2 gas permeance and O2/N2 and CO2/CH4 selectivity via intelligently decoupling the effects of elongational and shear rates on dense-selective layer and optimizing spinning conditions in dual-layer hollow fiber fabrication. The dual-layer polyethersulfone hollow fiber membranes developed in this work exhibit an O2/N2 selectivity of 6.96 and an O2 permeance of 4.79 GPU which corresponds to an ultrathin dense-selective layer of 918 Å at room temperature. These hollow fibers also show an impressive CO2/CH4 selectivity of 49.8 in the mixed gas system considering the intrinsic value of only 32 for polyethersulfone dense films. To our best knowledge, this is the first time to achieve such a high CO2/CH4 selectivity without incorporating any material modification. The above gas separation performance demonstrates that the optimization of dual-layer spinning conditions with balanced elongational and shear rates is an effective approach to produce superior hollow fiber membranes for oxygen enrichment and natural gas separation. 相似文献
93.
94.
An asymptotic theory based on multipole expansions is presented for multiparticle interactions in unbounded, weakly viscoelastic, creeping flows. The theory accounts for non-Newtonian sphere–sphere interactions that are of order O(De(a/R)2), where De is the Deborah number, a the sphere radius and R is the sphere–sphere separation. Analytic expressions are derived for the non-Newtonian correction to the multisphere mobility matrix for non-neutrally buoyant sedimenting spheres, and for neutrally buoyant spheres suspended in a shear flow. It is shown that these expressions give rise to particle chaining in simulations of interacting spherical particles. 相似文献
95.
一种探针-样品距离的切变力控制新方法 总被引:1,自引:1,他引:0
报道了近场扫描光学显微镜(Near-filed Scanning Optics Microscope NSOM)中一种基于切变力的探针 样品间距控制新方法.条形压电蜂鸣器片的上表面电极被沿着中心线分成两半,一半用于驱动,其上施加振荡源谐振频率进行激励,另一半上粘附光纤探针,并利用压电效应作为光纤探针的振幅传感器.当受振动激励的光纤探针由远处逐渐接近样品表面时,由于样品与探针之间的切变力阻尼作用使得探针的振幅减小,通过检测探针振幅的变化可以控制探针与样品的间距.我们建立了一套探针 样品间距探测控制系统并利用该系统获得了CD盘片表面8μm×8μm范围内的切变力形貌图. 相似文献
96.
Motoaki Kimura Steve Tung James Lew Chih-Ming Ho Fukang Jiang Yu-Chong Tai 《Fluid Dynamics Research》1999,24(6):679-342
Measurements of wall shear-stress streaks of a turbulent boundary layer in the channel flow were carried out using a MEMS-based micro-shear-stress imaging chip, which contains about 100 sensors. The chip is designed and fabricated by surface micromachining technology. One arrray of 25 micro-shear-stress sensors in the chip that covers a length of 7.5 mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The statistics of high shear-stress streaks were established. Based on the measurement, the physical quantities associated with the high shear-stress streaks, such as their length, width and peak shear-stress level, were obtained. We found out that a high correlation exists between the peak shear-stress level and front-end shear-stress slope of a high shear-stress streak. This important property is currently being applied to the deisgn of a real-time flow control logic. 相似文献
97.
This paper describes the application of multiple beam shearing interferometry to a position magnifying sensor. A multiple beam shearing interferometer (MBSI) with a shear plate wedged in the vertical direction produces sharp multiple beam fringes. When the lateral displacement of a point source (which gives rise to the input beam of the MBSI) or its image occurs in the horizontal direction, these fringes move vertically in a magnified manner. This characteristic was used in a position magnifying sensor to detect the displacement of a point image. The advantages of the sensor include a large displacement magnification (more than a hundred times) and a large working distance. 相似文献
98.
Daisuke Sawai Mika Miyamoto Tetsuo Kanamoto Masayoshi Ito 《Journal of Polymer Science.Polymer Physics》2000,38(19):2571-2579
No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution‐cast films or their drawn products, generally shows no small‐angle X‐ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm−1 ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (ta) and the temperature (Ta). Depending on ta, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (ta = 0.5–3 min, depending on Ta), rapidly increased in stage II (ta = 0.5–8 min), and stayed at a constant value characteristic for each Ta at yet longer ta's in stage III. The lamellar thickness characteristic for Ta increased rapidly with increasing Ta at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (Tm = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the Tm is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide‐angle X‐ray diffraction. The structural changes associated with annealing are also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2571–2579, 2000 相似文献
99.
100.
Kerim Isik Yoshinori Yoshida Lin Chen Till Clausmeyer A. Erman Tekkaya 《Comptes Rendus Mecanique》2018,346(8):770-778
This paper presents a methodology to model a blanking process using a continuum mechanical damage model. A variant of the Lemaitre model, in which the quasi-unilateral conditions are taken into consideration to modify the damage behavior under compressive stress states, is selected as material model. S45C high-carbon steel is analyzed experimentally. To characterize the damage behavior of the material, notched round bar tensile tests with three different notch radii (6 mm, 10 mm, and 20 mm) using image analysis are performed. Using digital image processing, the strain at the deformation zone can be computed for the load–strain curves. Those curves are used as an objective function to determine the parameters of the Lemaitre damage model. The experimental results are compared with the results of the FE analysis of the tensile test. The identified model parameters are used in numerical investigations of axisymmetric blanking. The effect of the model's extension to quasi-unilateral damage evolution is discussed. The crack progress in high-carbon steel sheet during blanking and the final sheared part morphology are predicted and compared with the experimental results. Sheared surface and burr height obtained by the analysis coincide with the results of the blanking experiment. 相似文献