The increased attention has been focused on the re-searches of soft materials proposed by Pierre-Gilles de Gennes, a Nobel Prize Laureate in Physics. A special issue of “Science” on soft surfaces was published in 2002 to review specific surface properti… 相似文献
Sodium succinate sulfate (MAPEG1500-OSO3Na) was prepared using maleic anhydride (MA) and polyethylene glycols (PEG1500) as raw materials. The structure was characterized by Fourier transform infrared spectrometry (FTIR) and 1H-nuclear magnetic resonance (1H NMR). Its physicochemical properties, such as surface activity, adsorption behavior, spreading performance, and rheological property, were investigated by static/dynamic surface tension (DST) measurements, contact angle techniques, and rheological techniques at 25°C. Surface tension measurement for this surfactant is about 17?mN/m. The DST results indicated that the adsorption process is mixed diffusion-kinetic adsorption mechanism. The spreading measurement demonstrated that MAPEG1500-OSO3Na possessed an excellent spreading ability. Besides, the dispersion performances of MAPEG1500-OSO3Na on barium sulfate (BaSO4) particles under different conditions have been studied by the weighing method and transmission electron microscope (TEM). These results showed that there exist optimum pH value and added amount of MAPEG1500-OSO3Na corresponding to the highest dispersion rate. 相似文献
Velocities of motion V of advancing meniscus of water in quartz capillaries with radii from 45 to 270 nm was directly measured using an optical microscope. In the case, when the meniscus advanced over the wetting film that is remained after the previous meniscus receding, hysteresis was not observed, and the wetting was complete. When the meniscus advanced over the yet unwetted surface, the dynamic contact angle d greatly depended on V, this dependence was the more pronounced, the smaller the r value. As the velocity V increases to 10–3 cm s–1, the value of d rises to 60°–70° reaching the plateau. Preliminary adsorption of water vapors on the capillary surface markedly decreases the values of d. The results obtained cannot be explained in terms of hydrodynamic and barrier theories of the contact angle. It was assumed that the controlling factor is the kinetics of vapor adsorption on the capillary surface in front of advancing meniscus. 相似文献
We report on the wetting dynamics of a 4.3 μL deionized (DI) water droplet impinging on microtextured aluminum (Al 6061) surfaces, including microhole arrays (hole diameter 125 μm and hole depth 125 μm) fabricated using a conventional microcomputer numerically controlled (μ-CNC) milling machine. This study examines the influence of the texture area fraction ?(s) and drop impact velocity on the spreading characteristics from the measurement of the apparent equilibrium contact angle, dynamic contact angle, and maximum spreading diameter. We found that for textured surfaces the measured apparent contact angle (CA) takes on values of up to 125.83°, compared to a CA of approximately 80.59° for a nontextured bare surface, and that the spreading factor decreases with the increased texture area fraction because of increased hydrophobicity, partial penetration of the liquid, and viscous dissipation. In particular, on the basis of the model of Ukiwe and Kwok (Ukiwe, C.; Kwok, D. Y. Langmuir 2005, 21, 666), we suggest a modified equation for predicting the maximum spreading factor by considering various texturing effects and wetting states. Compared with predictions by using earlier published models, the present model shows better agreement with experimental measurements of the maximum spreading factor. 相似文献
A new methodology capable of providing reliable and reproducible contact angle (theta) data has been employed to study the effect of clinical treatments grinding, acid etching, and deproteinization on medial dentin tissue. It is based on the application of the ADSA-CD algorithm to the determination of low-rate dynamic contact angles, obtained from slowly growing drops, and on contact angle measurement, as well as spreading behavior analysis, during the relaxation of the system (water on treated dentin) after initial drop growth. The theta data obtained were substantially more reproducible than those obtained with classical methods. A net effect of the treatment on theta was found, increasing dentin wettability: theta (polished) >theta (etched) >theta (deproteinized). The spreading rates correlate with the angles and are adequate for the dentin surface characterization. ANOVA and SNK tests show that for advancing contact angles the means corresponding to all treatments are significantly different. In the relaxing phase, mean angle and spreading rates on polished dentin differ significantly from those on etched and deproteinized dentin, but the latter do not differ significantly from each other. 相似文献
The initial stages of spontaneous spreading of a solvent drop (toluene) on the surface of a soluble polymer (polystyrene)
have been studied with a high-speed camera. For drops of 1–4 μL volume, the increase in contact radius r can be described by a power law r μ ta r \propto {t^{\alpha }} , with the spreading exponent α = 0.50 and for the first ≈8 ms. Thereafter, the three-phase contact line was pinned leading to a macroscopic static contact
angle of Θ0 = 12–15°. The insoluble liquids ethanol (α = 0.47, Θ0 = 0) and water (α = 0.35, Θ0 = 90°) showed a slower spreading. We attribute the fast spreading of toluene to the strong interaction with the polymer,
like in reactive wetting. The finite macroscopic contact angle indicates the formation of a ridge by softening of polystyrene
due to permeated toluene and the subsequent plastic deformation by the surface tension of the liquid. This interpretation
is supported by experiments on polymers grafted from a silicon wafer. Toluene completely wets polymer brush surfaces. Transport
of toluene through the vapor phase plays a significant role. 相似文献
The wetting and spreading of nanofluids composed of liquid suspensions of nanoparticles have significant technological applications. Recent studies have revealed that, compared to the spreading of base liquids without nanoparticles, the spreading of wetting nanofluids on solid surfaces is enhanced by the structural disjoining pressure. Here, we present our experimental observations and the results of the statics analysis based on the augmented Laplace equation (which takes into account the contribution of the structural disjoining pressure) on the effects of the nanoparticle concentration, nanoparticle size, contact angle, and drop size (i.e., the capillary and hydrostatic pressure); we examined the effects on the displacement of the drop-meniscus profile and spontaneous spreading of a nanofluid as a film on a solid surface. Our analyses indicate that a suitable combination of the nanoparticle concentration, nanoparticle size, contact angle, and capillary pressure can result not only in the displacement of the three-phase contact line but also in the spontaneous spreading of the nanofluid as a film on a solid surface. We show here, for the first time, that the complete wetting and spontaneous spreading of the nanofluid as a film driven by the structural disjoining pressure gradient (arising due to the nanoparticle ordering in the confined wedge film) is possible by decreasing the nanoparticle size and the interfacial tension, even at a nonzero equilibrium contact angle. Experiments were conducted on the spreading of a nanofluid composed of 5, 10, 12.5, and 20 vol % silica suspensions of 20 nm (geometric diameter) particles. A drop of canola oil was placed underneath the glass surface surrounded by the nanofluid, and the spreading of the nanofluid was monitored using an advanced optical technique. The effect of an electrolyte, such as sodium chloride, on the nanofluid spreading phenomena was also explored. On the basis of the experimental results, we can conclude that a nanofluid with an effective particle size (including the electrical double layer) of about 40 nm, a low equilibrium contact angle (<3°), and a high effective volume concentration (>30 vol %) is desirable for the dynamic spreading of a nanofluid system with an interfacial tension of 0.5 mN/m. Our experimental observations also validate the major predications of our theoretical analysis. 相似文献
The spreading of polymer nanodroplets upon a sudden change from partial to complete wetting on an ideally flat and structureless solid substrate has been studied by molecular dynamic simulations using a coarse‐grained bead‐spring model of flexible macromolecules. Tanner's law for the growth of the lateral droplet radius {R(t) ∝ t0.1} is found to hold as long as the droplet does not disintegrate into individually moving chains. The data for the contact angle θ following from Tanner's law correspond to a dependence on time {θ(t) ∝ t−0.3}. Our analysis of the mean square displacements of the polymer centers of mass reveals several dynamic regimes during the process of spreading. PACS numbers: 68.10.Gw, 05.70.Ln, 61.20.Ja, 8.45.Gd.
Molecular dynamics results for the average mean square displacement of all polymer chains plotted vs. time for a broad range of values for εwall. 相似文献
Hydrophobic and oleophobic surfaces with multi-scale structures were prepared on epoxy coating surfaces by using a facile process with fluorosilicone copolymer and SiO2 nano-particles. The fluorosilicone copolymers were synthesized using perfluoroalkyl acrylate (FA), vinyltriethoxysilane (VTES) and styrene (St) as comonomers via radical emulsion polymerization. In this paper, the surface properties of epoxy coating modified by fluorosilicone copolymer and SiO2 nano-particles were analyzed by using the contact angle measurement. The results showed that the modified epoxy coating surface exhibited not only excellent hydrophobicity but also oleophobicity, the water contact angle reached as high as 149° and the oil (atoleine) contact angle 101°, respectively. 相似文献
The effect of temperature T and weight-average molecular weight M?w on the rate of spreading of polystyrene melts on plane solid surfaces has been examined. The activation energy E of spreading was estimated to be 25.2 ± 3 kcal/mole, which is of the same magnitude as the activation energy for flow of polystyrene melts. The rate of spreading was found to be inversely proportional to M?w raised to the 1.5 power. This rate of spreading, measured as the time rate of increase in the liquid–solid contact area, dA/dt, could be expressed as where γ1v is the melt surface tension and θd and θs are the dynamic and static contact angles, respectively. The numerical value of K has been calculated to be (6.025 ± 3.693) × 10?14 in the temperature range of 110–260°C and for the values of M?w from 2000 to 37000. 相似文献
Foaming properties and the dynamic surface tension (DST) were carried out with aqueous solutions of sodium branched-alkyl benzene sulfonates to elucidate the relationship between foaming properties and surfactant structures. The parameters of the DST (t*, n, R1/2) are correlated with the foaming ability for alkyl benzene sulfonates with benzene ring substituting at positions 2, 4, and 8 of hexadecane. The parameters of the DST (t*, n, R1/2) are correlated with the foaming ability of the same surfactant solutions. The results indicated that the molecular diffusion in the solution, adsorption, and arrangement at the air/water interface were changed with different molecular structures: changing the substituted position of benzene ring from 2 to 8 of hexadecane, the value of t* and n decrease, and the value of R1/2 increases, which lead to the high dynamic surface activity and high foam volume. The foam stability is correlated with the high surface dilational elasticity and the strength of surface monolayer: changing the substituted position of benzene ring from 2 to 8 of hexadecane, the branched-alkyl chain becomes more flexible, which is characterized by densely packed adsorbed molecules and high film elasticity of the adsorption film. Therefore, the foam stability increases. 相似文献
The paper reports on the wetting characterization of two surfaces presenting reentrant shapes at micro- and nanoscale using low surface tension liquids (down to 28 mN/m). On the one hand, mushroom-like microstructures are fabricated by molding poly(dimethylsiloxane) (PDMS) onto a patterned sacrificial photoresist bilayer. On the other hand, zinc oxide nanostructures (ZnO NS) are synthesized by easy and fast chemical bath deposition technique. The PDMS and ZnO NS surfaces are then chemically modified with 1H,1H,2H,2H-perfluorodecyltrichlorosilane in vapor phase. Both PDMS and ZnO NS surfaces exhibit a large apparent contact angle (>150°) and contact angle hysteresis varying from 50° to a quasi-null value. This large discrepancy can be ascribed to the length scale and topography of the structures, promoting either a vertical imbibition or a lateral spreading within the roughness. 相似文献
The spontaneous spreading of ionic liquids on a fluoropolymer surface (Teflon AF1600) in air is investigated by high-speed video microscopy. Six ionic liquids (EMIM BF(4), BMIM BF(4), OMIM BF(4), EMIM NTf(2), BMIM NTf(2) and HMIM NTf(2)) are used as probe liquids. The dependence of the dynamic contact angle on contact line velocity is interpreted with a hydrodynamic model and a molecular-kinetic model. The usefulness of the hydrodynamic model is rather limited. There is a good correspondence between the molecular dimensions of the liquids and the physical parameters of the molecular-kinetic model. The viscous and molecular-kinetic contributions to energy dissipation are calculated, revealing that energy is dissipated in the bulk as well as at the contact line during dynamic wetting. There are wide ramifications of these results in areas ranging from lubrication and biology to minerals processing and petroleum recovery. 相似文献
The dynamics of super-twisted nematic (STN) liquid crystal displays was studied by detailed computer simulation. The time evolution of director configuration and velocity of flow as obtained by solving Ericksen-Leslie hydrodynamic equations. The influence of d/p value and pretilt angle on the dynamic response was also studied. A comparison was also made between twisted nematic and STN liquid crystal displays. 相似文献
Simulations of a droplet impacting a flat solid surface with a small initial speed have been studied using molecular dynamics. Approximating the shape of the drop by a spheroid, spreading radii, and dynamic contact angles are measured. The data reproduce well experimental results from literature. We show that the difference between the equilibrium and the dynamic contact angle cosines, that is, the spontaneous driving force, versus the spreading velocity of the three-phase line varies with impact speed and consists of two distinct regimes which can be described by existing models of moving contact lines. 相似文献