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61.
Jinlian Hu Bipin Kumar Harishkumar Narayana 《Journal of Polymer Science.Polymer Physics》2015,53(13):893-898
Like shape memory polymers, a novel phenomenon of stress memory was shown in which the stress of a material can respond to an external stimulus. This concept was further enlightened by a switch‐spring‐frame model that would eliminate the limitation of existing models which overlooked the stimulus responsive nature of such polymers. The discovery being reported in this article was stemmed from a real case study into shape memory polymer fibers in compression stocking for varicose veins. The breakthrough of stress memory enabled researchers to develop applications needing stimuli‐responsive forces, which can broaden the horizon of such smart polymers in emerging smart products in many multidisciplinary fields such as sensors, stress garments, and massage devices, electronic skins, and artificial muscles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 893–898 相似文献
62.
Xiaoming Chen Guoqing Qian Max A. Molleo Brian C. Benicewicz Harry J. Ploehn 《Journal of Polymer Science.Polymer Physics》2015,53(21):1527-1538
This work investigates the effects of polymer solids content and macromolecular structure on the high temperature creep behavior of polybenzimidazole (PBI) gel membranes imbibed with phosphoric acid (PA) after preparation via a polyphosphoric acid (PPA) mediated sol‐gel process Low‐solids, highly acid‐doped PBI membranes demonstrate outstanding fuel cell performance under anhydrous, ambient pressure, and high temperature (120–200 °C) operating conditions. However, PBI membranes are susceptible to creep under compressive loads at elevated temperatures, so their long‐term mechanical durability is a major concern. Here, we report results for the creep behavior of PBI membranes subject to compression at 180 °C. For para‐ and meta‐PBI homopolymers, increasing polymer solids content results in lower creep compliance and higher extensional viscosity, which may be rationalized by increasing chain density in the sol‐gel network. Comparing various homo‐ and copolymers at similar solids loading, differences in creep behavior may be rationalized in terms of chain–chain and chain‐solvent interactions that control macromolecular solubility and stiffness in the PA solvent. The results demonstrate the feasibility of improving the mechanical properties of PA‐doped PBI membranes by control of polymer solids content and rational design of PBI macromolecular structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1527–1538 相似文献
63.
Intrinsic Flexibility of the Zeolitic Imidazolate Framework ZIF‐7 Unveiled by CO2 Adsorption and Hg Intrusion 下载免费PDF全文
Dr. Marc Pera‐Titus 《Chemphyschem》2014,15(8):1581-1586
ZIF‐7, built as an assembly of ZnII centers and benzimidazolate ligands, shows prominent S‐shaped isotherms upon CO2 adsorption that can be attributed to sorbate‐induced gate‐opening phenomena involving a narrow‐to‐large pore phase transition. This peculiar sorption pattern can be captured via the formulation of thermodynamic isotherms, providing a direct enthalpic and entropic view of the gate‐opening process. Relying on such an approach, an energy barrier with preferential enthalpic nature for CO2 adsorption/desorption in the gate‐opening region could be unveiled. Moreover, the elastic energy involved during the gate‐opening process was revisited to 1.4–2.8 kJ mol?1 of solid in the temperature range 273–323 K, matching the value measured by isostatic compression of a ZIF‐7_lp sample filled with DMF and showing a dominant entropic contribution. 相似文献
64.
The Compressibility of pH‐Sensitive Microgels at the Oil–Water Interface: Higher Charge Leads to Less Repulsion 下载免费PDF全文
Dipl.‐Chem. Karen Geisel Prof. Dr. Lucio Isa Prof. Dr. Walter Richtering 《Angewandte Chemie (International ed. in English)》2014,53(19):4905-4909
pH‐responsive microgels are unique stabilizers for stimuli‐sensitive emulsions that can be broken on demand by changing the pH value. However, recent experiments have indicated that electrostatic interactions play a different role to that in conventional Pickering emulsions. The influence of charges on the interactions between microgels at the oil–water interface is now described. Compression isotherms of microgels with different charge density and architecture were determined in a Langmuir trough, and counter‐intuitive results were obtained: Charged microgels can be compressed more easily than uncharged microgels. The compressibility of microgels is thus not determined by direct Coulomb repulsion. Instead, the different swelling of the microgels in the charged and the uncharged states is proposed to be the key parameter. 相似文献
65.
Stanelle RD Mignanelli M Brown P Marcus RK 《Analytical and bioanalytical chemistry》2006,384(1):250-258
Microbore columns utilizing polypropylene capillary-channeled polymer (C-CP) fibers as the stationary phase in high-performance
liquid chromatography (HPLC) have been investigated. The polypropylene C-CP fiber diameter is ∼50 μm, with eight channels
along the periphery of the fiber ranging in diameter from ∼12 to 35 μm. The polypropylene C-CP fibers were packed into fluorinated
ethylene propylene (FEP) tubing, 1.3 mm inner diameter, with lengths of 500, 750, and 1,000 mm, to examine the effects of
increased column length with regards to plate height, resolution and analysis time. The low backpressures characteristic of
the C-CP fiber stationary phases allow the length of the column to be increased without significantly decreasing the specific
permeability. The high specific permeability (∼5×10−8 cm2) of the C-CP packed microbore columns yields a relatively low backpressure of 2.35 MPa at the highest flow rate of 17 μL/s
(54 mm/s) for a 1,000 mm column. Radial compression of the soft-walled FEP tubing is accomplished by pulling the 1.7 mm o.d.
column through a 1.4 mm diameter orifice. Reducing the inner diameter of the column from 1.3 to 1.0 mm lowered the interstitial
fraction from 47% to 42%, decreased the A-term contributions to band broadening, resulted in a significant decrease in average
plate height (∼30%), and increased resolution (∼36%) at identical linear velocities. Although the lower void volume of the
radially compressed column increased the backpressure from 0.57 to 2.11 MPa at a linear velocity of ∼20 mm/s, the specific
permeability only decreased from ∼7×10−8 to 4×10−8 cm2.
相似文献
66.
Zheng Deng Chang‐Jong Kang Mark Croft Wenmin Li Xi Shen Jianfa Zhao Richeng Yu Changqing Jin Gabriel Kotliar Sizhan Liu Trevor A. Tyson Ryan Tappero Martha Greenblatt 《Angewandte Chemie (International ed. in English)》2020,59(21):8240-8246
Given the consensus that pressure improves cation ordering in most of known materials, a discovery of pressure‐induced disordering could require recognition of an order–disorder transition in solid‐state physics/chemistry and geophysics. Double perovskites Y2CoIrO6 and Y2CoRuO6 polymorphs synthesized at 0, 6, and 15 GPa show B‐site ordering, partial ordering, and disordering, respectively, accompanied by lattice compression and crystal structure alteration from monoclinic to orthorhombic symmetry. Correspondingly, the long‐range ferrimagnetic ordering in the B‐site ordered samples are gradually overwhelmed by B‐site disorder. Theoretical calculations suggest that unusual unit‐cell compressions under external pressures unexpectedly stabilize the disordered phases of Y2CoIrO6 and Y2CoRuO6. 相似文献
67.
68.
Most of the literature on coded excitation describes the signal-to-noise ratio gain of a coded waveform in terms of the time-bandwidth product. We have shown that in the context of ultrasound imaging, the expression for the SNR gain provided by matched filtering a coded waveform, can be reduced to the total number of chips in the transmit signal. Hence, the SNR gain is independent of both the bandwidth and the duration of a single-chip. This concept is described in detail, clarifying this seeming contradiction. The impact of bandwidth and pulse duration on the SNR, SNR gain and axial resolution is described. Bandwidth requirements and the impact of regulatory peak-power limitations are also addressed. 相似文献
69.
提出分析中心裂纹板剪切断裂的断裂过程区D-B模型的叠加原理,考虑了压剪断裂的摩擦阻力和体现有限权宽影响的载荷修正,以非常简便的方法推导出计算断裂过程区长度和位移的公式。 相似文献
70.
This work seeks to determine how the mesostructure of seven types of cement composites containing alumina particles or not
controls their deviatoric strength, compaction law, and damage under high-pressure of confinement. First, the method of analysis
of quasi-oedometric compression tests is presented. Accuracy of the method for concrete is discussed by means of numerical
simulations. The confined compression tests performed show the effects of adding ceramic aggregates. Furthermore, an application
of post-mortem analysis by infiltration technique of each specimen is presented, revealing a highly micro-cracked pattern
depending of the mesostructure of these materials. From these observations, a discussion is presented on the influence that
the addition of ceramic aggregates exerts on the confined behaviour of these composites. The tests showed a highly beneficial
effect of the presence of particles, on both the deviatoric strength and the compaction law of the concretes considered. 相似文献