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991.
Dongsheng Wen 《Journal of nanoparticle research》2008,10(7):1129-1140
Research on nanofluids has progressed rapidly since their enhanced thermal conductivities were identified about a decade ago.
For boiling heat transfer with nanofluids, however, many contradictory results have been reported, which cannot be explained
by conventional theories developed for pure fluids. Recent progress in colloidal science shows that the presence of nanoparticles
could enhance the spreading and wettability of base fluids through a long-range structural disjoining pressure. This article
explores theoretically the influence of structural disjoining pressure to the nucleate boiling heat transfer through a four-zoned
microlayer evaporation model. The influence of particle size, particle concentration, and heat flux on the structural disjoining
pressure and the interfacial shape of the microlayer are investigated. The calculated equilibrium interfacial shape shows
that the meniscus is displaced toward the vapor phase in the presence of nanoparticles, an implication of enhanced wettability.
Such an improved wettability affects the number of active nucleate sites and bubble dynamics significantly, which could be
one of the important parameters that is responsible for the controversy of boiling heat transfer with nanofluids reported
in the literature. 相似文献
992.
A combination Monte Carlo and equivalent-continuum simulation approach was used to investigate the structure-mechanical property
relationships of titania nanoparticle deposits. Films of titania composed of nanoparticle aggregates were simulated using
a Monte Carlo approach with diffusion-limited aggregation. Each aggregate in the simulation is fractal-like and random in
structure. In the film structure, it is assumed that bond strength is a function of distance with two limiting values for
the bond strengths: one representing the strong chemical bond between the particles at closest proximity in the aggregate
and the other representing the weak van der Waals bond between particles from different aggregates. The Young’s modulus of
the film is estimated using an equivalent-continuum modeling approach, and the influences of particle diameter (5–100 nm)
and aggregate size (3–400 particles per aggregate) on predicted Young’s modulus are investigated. The Young’s modulus is observed
to increase with a decrease in primary particle size and is independent of the size of the aggregates deposited. Decreasing
porosity resulted in an increase in Young’s modulus as expected from results reported previously in the literature. 相似文献
993.
Hongjin Jiang Kyoung-sik Moon Yangyang Sun C. P. Wong Fay Hua Tarasankar Pal Anjali Pal 《Journal of nanoparticle research》2008,10(1):41-46
Shape and size controlled gram level synthesis of tin/indium (SnIn) alloy nanoparticles and nanobundles is reported. Poly(N-vinylpyrrolidone)
(PVP) was employed as a capping agent, which could control the growth and structure of the alloy particles under varying conditions.
Transmission electron microscopy showed that unique SnIn alloy nanobundles could be synthesized from the bulk materials above
a certain concentration of PVP and below this concentration, discrete spherical nanoparticles of variable size were evolved.
The morphology and the composition of the as-synthesized SnIn alloy nanobundles were investigated by high-resolution transmission
electron microscopy (TEM). The possible mechanisms on the formation of these structures were discussed. 相似文献
994.
CdS hollow/solid nanospheres and their chain-structures were successfully synthesized through supporting liquid membrane (SLM) system with bio-membrane. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), UV–Vis spectroscopy, and photoluminescence (PL) spectroscopy have been used for the characterization of the products. The average diameters of CdS solid/hollow spheres are about 10, 40 nm, respectively. The wall of the hollow spheres is about 5 nm. CdS products are all cubic face-centered structure with the cell constant a = 5.830 Å. We also explore the morphology, structure and possible synthesis mechanism. A possible template mechanism has been proposed for the production of the hollow CdS nanocrystals, that is, CdS nanoparticles grow along the non-soakage interface between CHCl3 and reactant solution. During this process, the organic functional groups were crucial to the control of crystal morphologies. 相似文献
995.
Nanoparticles are ubiquitous in environment and are potentially important in many environmental processes such as sorption,
coprecipitation, redox reactions, and dissolution. To investigate particle size effects on nanoparticle aggregation and stability,
this study tested aggregation behavior of 12(±2), 32(±3), and 65(±3) nm (hydrated radius) hematite particles under environmental
relevant pH and ionic strength conditions. The results showed that at the same ionic strength and pH conditions, different
particle sizes show different tendency to aggregate. At the same ionic strength, aggregation rates are higher for smaller
particles. The critical coagulation concentration also depends on particle size, and decreases as particle size decreases.
As the particle size decreases, fast aggregation shifted to lower pH. This may be related to a dependence of PZC on particle
size originating from change of structure and surface energy characteristics as particle size decreases. Under the same conditions,
aggregation occurs faster as particle concentration increases. Even though the nanoparticles of different sizes show different
response to the same pH and ionic strength, DLVO theory can be used to qualitatively understand hematite nanoparticle aggregation
behavior. 相似文献
996.
Prashant Mohanpuria Nisha K. Rana Sudesh Kumar Yadav 《Journal of nanoparticle research》2008,10(3):507-517
Nanotechnology involves the production, manipulation and use of materials ranging in size from less than a micron to that
of individual atoms. Although nanomaterials may be synthesized using chemical approaches, it is now possible to include the
use of biological materials. In this review, we critically assess the role of microorganisms and plants in the synthesis of
nanoparticles. 相似文献
997.
Zhiguo Liu Yuangang Zu Yujie Fu Songlin Guo Yuliang Zhang Huili Liang 《Journal of nanoparticle research》2008,10(8):1271-1278
A new kind of hybrid nanoparticles composed of copper ions and poly(p-phenylenediamine) has been synthesized in aqueous solution at room temperature. The nanoparticles have been characterized
and studied by TEM, AFM, XPS, and UV spectroscopy. The synthesized nanoparticles are prone to connect with each other and
form large nanoclusters. The diameters of the nanoparticles are 46 ± 26 nm. It is believed that a porous network structure
exists inside the nanoparticles. The UV absorption spectra of the nanoparticles are sensed with pH and can be reversibly changed
according to the pH level. This phenomenon of the nanoparticles has some potential applications. Nanosheets and branched rods
composed of copper ions and poly(p-phenylenediamine) have also been obtained by using different ratios of copper ions and p-phenylenediamine as the initial reactant. 相似文献
998.
Leszek Bychto Maria Balaguer Ester Pastor Vladimir Chirvony Eugenia Matveeva 《Journal of nanoparticle research》2008,10(8):1241-1249
The time changes of photoluminescence (PL) characteristics of porous silicon (porSi) powder during storing in different ambients
have been reported. A porous silicon material with embedded Si nanocrystals of size of few nanometers was prepared by an electrochemical
method from 10 to 20 Ωcm p-type Si wafers, and both constant and pulse current anodization regimes were used. A powder with
a submicron average particle size was obtained by simple mechanical lift-off of the porous layer followed by additional manual
milling. The air, hexane, and water as storage media were used, and modification by a nonionic surfactant (undecylenic acid)
of the porSi surface was applied in the latter case. Dependence of PL characteristics on preparation and storage conditions
was then studied. A remarkable blue shift of a position of PL maximum was observed in time for porSi powders in each storage
media. In water suspension a many-fold build-up (10–30) of PL intensity in a time scale of few days was accompanied by an
observed blue shift. Photoluminescence time behavior of porSi powders was described by a known mechanism of the change of
porSi PL from free exciton emission of Si nanocrystals to luminescence of localized oxidized states on the Si nanocrystal
surface. 相似文献
999.
S. Kawabata N. Ishikawa M. Mitsui A. Nakajima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):155-158
Uniform-sized silver nanoparticles with average diameter of 13.7 nm have been prepared in the gas-phase by combining a pulsed
laser ablation method
with a low pressure-differential mobility analyzer (LP-DMA). By depositing
the silver nanoparticles onto a silicon substrate, a granular film
consisting of size-selected silver nanoparticles has been fabricated and its
morphology and electronic properties have been examined using transmission
electron microscopy (TEM) and UV-visible absorption spectroscopy. This
granular silver film serves as a highly active substrate for
surface-enhanced Raman scattering (SERS). 相似文献
1000.
M. Dubiel R. Schneider H. Hofmeister K.-D. Schicke J. C. Pivin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):291-294
The formation of argentic clusters and very small Ag
nanoparticles of 0.5 to 2 nm size in commercial soda-lime glass silver-doped
by Ag/Na ion exchange in a mixed nitrate melt has been studied by electron
microscopy and EXAFS. Particles formation was induced already during the ion
exchange procedure, or by subsequent ion irradiation with 1.5 MeV He+
or 3 MeV Au+. The presence of nanoparticles was also macroscopically
revealed by their surface plasmon resonance. The structural characterization
indicates that specific configurations of silver oxide-like structures,
so-called argentic clusters, are involved in the initial stage of
nanoparticles formation. 相似文献