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Transition between superhydrophobic states on rough surfaces 总被引:11,自引:0,他引:11
Patankar NA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(17):7097-7102
Surface roughness is known to amplify hydrophobicity. It is observed that, in general, two drop shapes are possible on a given rough surface. These two cases correspond to the Wenzel (liquid wets the grooves of the rough surface) and Cassie (the drop sits on top of the peaks of the rough surface) formulas. Depending on the geometric parameters of the substrate, one of these two cases has lower energy. It is not guaranteed, though, that a drop will always exist in the lower energy state; rather, the state in which a drop will settle depends typically on how the drop is formed. In this paper, we investigate the transition of a drop from one state to another. In particular, we are interested in the transition of a "Cassie drop" to a "Wenzel drop", since it has implications on the design of superhydrophobic rough surfaces. We propose a methodology, based on energy balance, to determine whether a transition from the Cassie to Wenzel case is possible. 相似文献
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K. Usha Deniz E. B. Mirza P. S. Parvathanathan A. V. Patankar A. S. Paranjpe 《Molecular Crystals and Liquid Crystals》2013,570(2-4):271-276
The phase transitions occurring in nBABAs (n = 1 to 5), especially those involving the nematic phase, have been studied by DSC. Schemes of transition are presented and the chain length (n) dependences of the the transition temperatures and entropies are discussed. 相似文献
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A hitherto unknown mechanism for wetting transition is reported. When a pendant drop settles upon deposition, there is a virtual "collision" where its center of gravity undergoes rapid deceleration. This induces a high water hammer-type pressure that causes wetting transition. A new phase diagram shows that both large and small droplets can transition to wetted states due to the new deceleration driven and the previously known Laplace mechanisms, respectively. It is explained how the attainment of a nonwetted Cassie-Baxter state is more restrictive than previously known. 相似文献
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Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
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CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
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Magnetoelectric (ME) composites yBa0.8Pb0.2TiO3–(1−y)CuFe2O4 are prepared by ceramic method. The component phases are prepared from two different routes, viz. CuFe2O4 (ferrite phase) is prepared by oxalate precursor route and Ba0.8Pb0.2TiO3 (ferroelectric phase) by solid-state reaction route. No intermediate phases are observed in the composites containing these ferrite and ferroelectric phases. ME conversion factor (measure of ME effect) is found to be enhanced compared to those reported in the composites, in which the component phases were prepared by only one route, i.e. solid-state reaction route. The results on ME conversion are well accounted by measuring the complex impedance and analyzing their Nyquist plots. 相似文献
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It is common knowledge that flow around bluff bodies exhibits oscillatory behaviour. The aim of the present study is to compute the steady two-dimensional flow around a square cylinder at different Reynolds numbers and to determine the onset of unsteadiness through a linear stability analysis of the steady flow. Stability of the steady flow to small two-dimensional perturbations is analysed by computing the evolution of these perturbations. An analysis of various time-stepping techniques is carried out to select the most appropriate technique for predicting the growth of the perturbations and hence the stability of the flow. The critical Reynolds number is determined from the growth rate of the perturbations. Computations are then made for periodic unsteady flow at a Reynolds number above the critical value. The predicted Strouhal number agrees well with experimental data. Heat transfer from the cylinder is also studied for the unsteady laminar flow. 相似文献