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91.
92.
Effect of interfacial pretreatment on the properties of montmorillonite/poly(vinyl alcohol) nanocomposites 下载免费PDF全文
Shailesh Shori Xiaoming Chen Michael Peralta Hongsheng Gao Hans‐Conrad zur Loye Harry J. Ploehn 《应用聚合物科学杂志》2015,132(18)
This work explores the factors that control the dispersion of exfoliated montmorillonite (MMT) in poly(vinyl alcohol) (PVOH) during solution blending and solvent evaporation. Nanocomposite films were prepared by solution blending of aqueous PVOH solutions with dilute suspensions of fully exfoliated MMT platelets (as confirmed by AFM). Dynamic light scattering (DLS) indicates that addition of MMT suspensions to PVOH solutions results in undesired particle aggregation and thus poor MMT dispersion in cast films (as evidenced by transmission electron microscopic images and gas permeation measurements). We believe that PVOH bridging induces MMT platelet aggregation. To counteract bridging aggregation, we explore the novel idea of pretreating the MMT surface with a small amount of compatible polymer prior to solution blending with PVOH. We hypothesize that “pretreating” the MMT platelet surfaces with adsorbed polymer in dilute suspensions will protect the platelets from bridging aggregation during solution blending and solvent evaporation. MMT/PVOH composite films have been prepared using low‐molecular‐weight PVOH as the pretreatment polymer; and low‐, medium‐, and high‐molecular‐weight PVOH as the matrix polymer. A PEO‐PPO‐PEO triblock copolymer (F108 from the Pluronics® family) was also evaluated as the pretreatment polymer. DLS shows that pretreated MMT platelets are less susceptible to aggregation during blending with PVOH solutions. Results compare the crystalline structure, thermal properties, dynamic mechanical properties, gas permeability, and dissolution behavior of MMT/PVOH films incorporating untreated versus pretreated MMT. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41867. 相似文献
93.
Shailesh Vidhate Lucia Innocentini‐Mei Nandika Anne D'Souza 《Polymer Engineering and Science》2012,52(6):1367-1374
In this work, nanocomposites of poly(hydroxybutyrate‐co‐hydroxyvalerate) PHBV and multiwalled carbon nanotubes (MWNT) were prepared by melt blending. Mechanical, thermal, morphological, and electrical properties of the prepared PHBV/MWNT nanocomposites were investigated. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) results showed MWNT effectively enhanced the crystallization and nucleation of PHBV. Dynamic thermo‐mechanical and static uniaxial mechanical tensile and compressive properties were increased by the addition of MWNT. MWNT observed in the nanocomposites using transmission electron microscopy (TEM) showed dimensions similar to separated nanotubes inferring a good dispersion. The presence of nanotubes in close vicinity with each other formed an interconnecting network that led to the formation of electrically conductive nanocomposites. The electrical resistance of the nanocomposites was reduced with the addition of MWNT. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers 相似文献
94.
Longzhou Ma Keh-Minn Chang Sarwan K. Mannan Shailesh J. Patel 《Metallurgical and Materials Transactions A》2002,33(11):3465-3478
The effect of isothermal exposure on the elevated-temperature, time-dependent fatigue-crack propagation (FCP) in INCONEL Alloy
783 is investigated. Commercially produced Alloy 783 was annealed and aged following the standard heat-treatment procedure.
One set of specimens was then isothermally exposed at 500 °C for 3000 hours. All specimens were subjected to FCP tests with
various hold-time periods and sustained-loading crack-growth tests at 538 °C and 650 °C in a laboratory-air environment. Without
a hold time, the as-produced and isothermally exposed materials had comparable FCP rates at both test temperatures. With hold
times of 100 and 300 seconds, the as-produced and isothermally exposed specimens had comparable FCP rates at 538 °C. Hold-time
testing of the as-produced material at 650 °C showed abnormal time-dependent FCP and sustained-loading crack-growth retardation.
However, hold-time testing of isothermally exposed material at 650 °C showed the steady sustained-loading crack growth and
fully time-dependent FCP typically observed in many superalloys. Comparison with Alloy 718 data from the literature shows
that FCP rates of as-produced Alloy 718 and isothermally exposed Alloy 783 are comparable at 650 °C. A fully time-dependent
FCP model based on the damage-zone concept and a thermal-activation equation is proposed to characterize the FCP behaviors. 相似文献
95.
Jinghua Fang Shailesh Kumar Donghan Seo Kostya Ostrikov 《Science and Technology of Advanced Materials》2014,15(5)
Various morphologies of the vertically-aligned graphene flakes were fabricated on the nanoporous templates treated with metal ions in solutions, as well as coated with a thin gold layer and activated in the low-temperature Ar plasma. The thickness and level of structural defects in the graphene flakes could be effectively controlled by a proper selection of the pre-treatment method. We have also demonstrated that various combinations of the flake thickness and defect levels can be obtained, and the morphology and density of the graphene pattern can be effectively controlled. The result obtained could be of interest for various applications requiring fabrication of large graphene networks with controllable properties. 相似文献
96.
Moh. Sattar Praveen Ch. DurgaPrasad Ajay Verma Shailesh Kumar Sangit Kumar 《Advanced Synthesis \u0026amp; Catalysis》2016,358(2):240-253
A mild and efficient palladium‐catalyzed synthetic method for the C H functionalization of N‐(quinolin‐8‐yl)ferrocenecarboxamide has been developed. Various aryl iodides containing I, NO2, CN, COMe, CO2Et, and NH functionalities and also alkyl iodides underwent the Pd‐catalyzed intermolecular carbon‐carbon bond forming reaction with ferrocenecarboxamide successfully which led to a diverse array of bis(aryl/alkyl)ferrocenecarboxamides in 34–92% yields. Cross‐coupling of the ferrocenyl C H bond with aryl iodides can also be achieved utilizing an economical Ni catalyst. Additionally, selective monoalkylation of ferrocenecarboxamide was studied using sodium bicarbonate as base and dibenzylphosphoric acid as additive under Pd‐catalyzed reaction conditions. Subsequently, removal of the directing group, 8‐aminoquinoline, from bis(aryl)ferrocenecarboxamides led to bis(aryl)ferrocenes bearing versatile methyl ester and carboxaldehyde functional groups.
97.
A nano-composite coating was formed using nano-Fe2O3 as pigments in different concentrations, to a specially developed alkyd based waterborne coating. The nano-Fe2O3 based composite coatings were applied on mild steel substrate by dipping. The dispersion of nano-Fe2O3 particles in coating system was investigated by SEM and AFM techniques. The effect of addition of these nano-pigments on the electrochemical behavior of the coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy (EIS). Coating modified with higher concentration of nano-Fe2O3 particles showed comparatively better performance as it was evident from Rpo and Cc values after 30 days of exposure. In general, the study showed an improvement in the corrosion resistance of the nano-particle modified coatings as compared to the neat coating, confirming the positive effect of nano-particle addition in coatings. 相似文献
98.
We propose an adaptive algorithm Adaptmin to create perfectly periodic schedules. A perfectly periodic schedule schedules a client regularly after a predefined amount of time known as the period of the client. The periodicity of such schedules can be used to save battery life of nodes in a wireless network. The quality of a perfectly periodic schedule is a function of the ratio between the granted and requested periods. We find a worst case performance bound on the quality of schedules produced by Adaptmin. We compare our algorithm to previously proposed algorithm A in [Z. Brakerski, A. Nisgav, B. Patt-Shamir, General perfectly periodic scheduling, in: Proc. 21st Annual Symp. on Principles of Distributed Computing, 2002, pp. 163-172], and show families of input instances where either Adaptmin does no worse than A, or always outperforms A. The better performance of the proposed algorithm is also confirmed by simulations results for randomly generated input instances. Adaptmin produces 25% more efficient schedules as compared to A in our experiments. We also propose a variant of Adaptmin which is computationally much less demanding compared to A, but is very close to Adaptmin in terms of efficiency. Finally, we compare our algorithms to exponential-time optimal scheduling. Our simulation results indicate that the performance of the proposed algorithms is close to that of optimal scheduling. 相似文献
99.
For an optimum performance of colloidal nanocrystal devices for a variety of applications such as photonic devices, solar cells and biological labelling, the determining factors are the nanocrystal surface and size. In this work, these two factors have been tuned via wet chemistry to tailor the material properties: The absorption and emission spectra have been tailored by choice of the nanocrystal size; nanocrystal shape by surface modification and photoluminescence (PL) efficiency determined by surface traps, has been tuned via appropriate selection of the nanocrystal capping ligands. Here, we have shown that through ligand-exchange process, the surface of the CdSe quantum dots (QDs) can be modified by replacing the longer-chain ligands of conventional trioctyl phosphine oxide (TOPO) or oleic acid (OA) with shorter-chain ligand of butyl amine. This imparts colloidal stability and water solubility to CdSe QDs for its potential applications in biosensors and biological imaging. It is conjectured that crystallite sizes, oxidation potential of CdSe QDs and stereochemical compatibility of ligands (TOPO, oleic acid and butyl amine) greatly influences the photophysics and photochemistry of CdSe QDs. 相似文献
100.
P. G. Mukunda Rao A. Shailesh Shrikantha S. Rao 《Metals and Materials International》2010,16(1):137-143
Although the manner in which the molten metal flows plays a major role in the formation of the uniform cylinder in centrifugal casting, not much information is available on this topic. The flow in the molten metal differs at various rotational speeds, which in turn affects the final casting. In this paper, the influence of the flow of molten metal of hyper eutectic Al-2Si alloys at various rotational speeds is discussed. At an optimum speed of 800 rpm, a uniform cylinder was formed. For the rotational speeds below and above these speeds, an irregular shaped casting was formed, which is mainly due to the influence of melt. Primary á-Al particles were formed in the tube periphery at low rotational speed, and their sizes and shapes were altered with changes in rotational speeds. The wear test for the inner surface of the casting showed better wear properties for the casting prepared at the optimum speed of rotation. 相似文献