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1.
We obtained monocrystalline droplets in a thermotropic cubic phase, of approximate size 100μm, deposited on a flat surface.
The facets of these soft crystals are explored using both an optical microscope and an AFM. The height of individual steps
on the principal facets and the lateral distance between steps in vicinal facets are measured using AFM in imaging (tapping)
mode. Moreover, the elastic modulus is measured locally, using the AFM tip (in contact mode) as a local rheological probe. 相似文献
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The factors influencing the state and wetting transition of droplets on a rough surface are both complex and obscure. The
change in wetting is directly reflected by changes under the contact condition of the droplets with the surface. The recent
study about the wettability of the superhydrophobic surface under the condensing condition arouses the new understanding about
the apparent state of droplets on a rough surface. In this work, to validate the existence of droplets in an intermediate
state, a microscale pillar topological polydimethylsiloxane (PDMS) surface was manufactured and its wettability under various
conditions was studied. According to the experimental data, it is proposed that the wetting state of a rough surface may be
embodied using the contact area ratio of a solid/liquid/gas droplet with the projective plane. A general calculation model
for the apparent contact angle of droplets is given and expressed diagrammatically. It is found that the measured apparent
contact angles of droplets at different states on the surface falls within the range predicted by our proposed equation.
Supported by the National Natural Science Foundation of China (Grant No. 50606025) 相似文献
4.
本文采用高速摄像仪对水滴和乙醇液滴撞击加热壁面后的蒸发过程进行了实验观测, 分析了液滴撞击加热壁面后的蒸发特性参数. 实验中, 两种液体初始温度均为20 ℃, 不锈钢壁面初始温度范围为68-126℃. 水滴初始直径为2.07 mm, 撞击壁面时Weber 数为2-44; 乙醇液滴初始直径为1.64 mm, Weber数为3-88. 结果表明, 液滴受到重力、表面张力及流动性的影响, 在蒸发过程的大部分时间内, 水滴高度持续降低而接触直径几乎不变; 蒸发后期, 液滴发生回缩, 水滴的接触直径、高度和接触角出现振荡现象. 乙醇液滴的接触角随时间的增加呈现先减小随后保持不变的趋势, 而接触直径和高度则持续减小, 直到液滴完全蒸发. 液滴蒸发总时长与液体物性和壁面温度有关, 随壁面温度的升高而减小, 与液滴撞击壁面时的Weber 数无关. 同时, 随着壁面温度的升高, 液滴显热部分占总换热量的比重增大, 显热部分能量不可忽略, 本文实验条件下得到水滴的平均热流密度为0.014-0.110 W·mm-2. 相似文献
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基于分子两体势,用Monte Carlo方法计算向列相液晶微滴.两体势基于格点模型,是空间各向异性的且依赖于液晶的弹性常数.假定向列相液晶微滴具有自由表面,引入切向内禀强度定量描写表面引发的分子内禀易取向的强弱.通过各向异性势的两种方案,在低温下计算切向内禀强度和二阶序参数在微滴内不同区域的变化,与Lebwohl-Lasher模型作对比分析.结果表明:只有一种方案在微滴表面产生内禀易取向,且内禀强度值的大小与K33/K11值有关;空间不完整的向列相液晶使得微滴由内层到外层有序度越来越低. 相似文献
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Daniela Fritter Charles M. Knobler Didier Roux Daniel Beysens 《Journal of statistical physics》1988,52(5-6):1447-1459
We describe computer simulations of the growth of breath figures, the patterns formed when droplets condense on a cold surface. The focus is on the coalescence of droplets, which is an important growth mechanism, and the conditions for self-similar patterns, which are experimentally observed. It is assumed that individual droplets grow according to a power law; droplets that touch coalesce instantly and are replaced by a new droplet at the center of gravity of the coalescing pair. The average droplet radius, distribution of droplet sizes, surface coverage, and radial distribution function are determined as a function of the time for a variety of initial coverages and polydispersities. These quantities are compared to those determined by experiment, and our simple model is found to be in good accord with the observed behavior. It is observed that the process of coalescence induces spatial correlation between droplets.This paper is dedicated to Howard Reiss on his 66th birthday. 相似文献
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Classical Rayleigh theory predicts an instability of a surface charged liquid sphere, when the Coulomb energy E(C) exceeds twice the surface energy E(S). Previously, electrified liquid droplets have been found to disintegrate at a fissility X=E(C)/2E(S) well below one, however. We determine the stability of charged droplets in an electrodynamic levitator by observing the amplitude and phase of their quadrupolar shape oscillations as a function of the fissility. With this novel approach, which does not rely on an independent determination of the charge and surface tension of the droplets, we are able to confirm for the first time the Rayleigh limit of stability at X=1 for micrometer sized droplets of ethylene glycol. 相似文献
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Based on the effective medium approximation theory of composites, the
whitecap-covered sea surface is treated as a medium layer of dense seawater
droplets and air. Two electromagnetic scattering models of randomly rough
surface are applied to the investigation of microwave backscattering of breaking
waves driven by strong wind. The shapes of seawater droplets are considered
by calculating the effective dielectric constant of the whitecap layer. The
responses of seawater droplets shapes, such as sphere and ellipsoid, to the
backscattering coefficient are discussed. Numerical results of the models are in
good agreement with the experimental measurements of horizontally and
vertically polarized backscattering at microwave frequency 13.9GHz and
different incidence angles. 相似文献
11.
We present a comparative study of gallium (Ga) and aluminium (Al) droplets fabricated on GaAs (100) and AlAs (100) surfaces. Higher density of Ga droplets is achieved on AlAs surface compared with GaAs surface. Similarly, the density of Al nanostructures is higher on AlAs surface than on GaAs surface, even though different morphologies are obtained on each surface. Further, while uniform Ga droplets are formed on both GaAs and AlAs surfaces, Al rings and dots, with big inhomogeneity, are observed on GaAs and AlAs surface, respectively. This investigation suggests that size and shape of nanostructures grown by the droplet epitaxy method can be designed by employing different surfaces. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
This article is a concise overview about the developing microfluidic systems named surface-tension-confined droplet microfluidics(STORMs). Different from traditional complexed droplet microfluidics which generated and confined the droplets by three-dimensional(3D) poly(dimethylsiloxane)-based microchannels, STORM systems provide twodimensional(2D) platforms for control of droplets. STORM devices utilize surface energy, with methods such as surface chemical modification and mechanical processing, to control the movement of fluid droplets. Various STORM devices have been readily prepared, with distinct advantages over conventional droplet microfluidics, which generated and confined the droplets by 3D poly(dimethylsiloxane)-based microchannels, such as significant reduction of energy consumption necessary for device operation, facile or even direct introduction of droplets onto patterned surface without external driving force such as a micropump, thus increased frequency or efficiency of droplets generation of specific STORM device, among others. Thus, STORM devices can be excellent alternatives for majority areas in droplet microfluidics and irreplaceable choices in certain fields by contrast. In this review, fabrication methods or strategies, manipulation methods or mechanisms,and main applications of STORM devices are introduced. 相似文献
13.
It is shown that a smectic A droplet deposited on a solid substrate treated for strong homeotropic anchoring is faceted at
the top in spite of the fact that there are no steps at the free surface, but instead edge dislocations in the bulk. The radius
of the facet and the full profile of the curved part of the droplet are determined as a function of the temperature in the
vicinity of a nematic-smectic A phase transition. It is shown that the observed profiles do not correspond to the actual equilibrium
shape, but to metastable configurations close to their point of marginal stability. In addition, we predict that the profiles
must be different for a given temperature depending on whether the droplet has been heated or cooled down to reach this temperature.
Finally, we discuss the problem of the formation of giant dislocations in big droplets (Grandjean terraces). 相似文献
14.
A. I. Aleksandrov N. A. Tebeneva V. G. Shevchenko I. A. Aleksandrov I. B. Meshkov A. M. Muzafarov 《JETP Letters》2017,105(1):51-54
Cholesteric droplets dispersed in a polymer with homeotropic surface anchoring are studied. A director configuration with the bipolar distribution of the axis of the helix is formed in droplets. The untwisting of the helical structure (i.e., an increase in the pitch of the helix) is experimentally observed at a decrease in the size of droplets. This dependence is analyzed for liquid crystal droplets with various concentrations of the chiral addition. A proposed empirical relation describes well the correlation of the helix pitch and the size of droplets in the studied samples. 相似文献
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A simple model for size-dependent surface tension of liquid binary alloy droplets has been established based on Bulter’s equation and our model for size-dependent surface tension of pure liquid component. As an example, the surface tension of liquid Bi–Sn alloy droplets are calculated and discussed. The results show that as the size of the liquid alloy droplets decreases, the corresponding surface tension decreases. The component with lower surface tension is enriched in the surface layer at all times while relatively more another component with higher surface tension appear in the surface region when the size decreases. The effect of decreasing size on liquid alloy surface tension is like that of increasing temperature. When size is larger than about 12 nm, the size effect is small and negligible. 相似文献
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利用有效介质近似理论方法,本文提出了计算强风驱动下海浪破碎的海洋表面微波辐射率的一种修正模式。该模式修正Pandey等人的经验模式,通过把海浪破碎的白冠层等效为海水和空气的复合介质,并利用复合介质有效介电常数的计算方法,在该模式中充分考虑了海洋表面水滴形态、白冠层厚度和覆盖率对海洋表面微波辐射率的影响。实验表明,该模式在不同风速、不同水滴形态以及微波频率下(6.6GHz,10.7GHz,37GHz)计算的海洋表面微波辐射率与实测结果一致。 相似文献
18.
Deeder M. Aurongzeb 《Solid State Communications》2005,134(3):165-169
Effect of temperature and surface tension on surface during sedimentation is studied using atomic force microscopy. Effects of surface tension is incorporated by using ∼1 mm radius water droplets. Surface tension of water droplet directed the deposition of dissolved particles around the perimeter of the droplet; leaving almost hollow circle in the middle with light deposition due to the particles being close to the surface. Evaporating shallow water solutions left random salt structures on the surface. Growth exponents are calculated along with the fractal dimension. For sedimentation process in shallow water (depth of ∼2 mm), a transition is observed from continuum model (1.88±0.2) to KPZ (0.406±0.082) universality class around ∼1 μm at room temperature. For droplets evaporation, turbulent (multi-affine) to self-affine transition is observed. Fractal dimensions (FD) for the droplets are found to be between one and two. The FD values are consistent with the fact that competing nonlinear terms are present in the system. 相似文献
19.
为了提高聚合物/液晶(HPDLC)光栅的衍射效率并改善光栅的表面形貌,研究了表面垂直取向处理对HPDLC光栅的影响。首先,研究了表面垂直处理对液晶分子的取向作用,发现垂直取向层对液晶的锚定作用随着盒厚的增加而逐渐减弱,取向层的作用范围大概在3 m ~5 m之间;其次,对相分离程度进行了实验表征,结果表明,随着液晶盒厚度的增加,相分离开始的时间越来越快,并且分离程度也越来越彻底。最后,讨论了表面垂直取向对HPDLC光栅衍射效率的影响,随着盒厚的增加,相分离出来的液晶微滴形成连续的区域,光栅的衍射效率逐渐升高,当盒厚增加到一定程度,其衍射效率和无取向处理的光栅接近。当盒厚过大时,垂直取向处理对HPDLC光栅散射损失并没有太大的改善,只有当盒厚适中(12 m)时,光栅的衍射效率最高,散射损失最小。 相似文献
20.
采用分子动力学模拟方法研究了改进的Simple pointcharge模型SPC/E水滴在Cu_(50)Zr_(50)非晶薄膜上的润湿行为和铺展过程.通过与CuZr(110)和(100)晶面对比研究发现,水滴在Cu_(50)Zr_(50)非晶薄膜表面上表现出较高的铺展速度.水滴在非晶合金表面的铺展过程中形成了明显的吸附层;而在晶态表面,水滴铺展前沿呈脚状形态.分析结果表明非晶表面的水分子在吸附层内呈现完全无序的单层排列方式,而在晶态表面,特别是(100)晶面,吸附层水分子呈双层有序排列.这种吸附层结构的差异导致了吸附层内水分子方向的差异:非晶表面吸附层内水分子方向倾向平行于表面,而晶态基底上吸附层内的水分子倾向于指向液滴内部.由此造成了非晶表面吸附层中的水分子与液滴内部以相对较弱的氢键相互作用,这使得上层水分子能够较容易扩散至吸附层前沿,促进液滴铺展. 相似文献