Correlation of nanoscale behaviour of forces and macroscale surface wettability (original) (raw)
Related papers
Chemical Physics Letters, 2003
We have measured the force acting on neutral tips as function of distance to hydrophobic surfaces in aqueous solutions. The unusually large magnitude of this force is attributed to an electrostatic response of the aqueous fluid structure (hydration layer). The exchange of a volume of this region with a dielectric permittivity int by the tip with a dielectric constant tip is responsible for the tip attraction when it is immersed in the hydration layer. Hydrophobic hydration layers, characterized by a variable dielectric permittivity profile, have measured widths of 4and4 and 4and8 nm for hydrophobic silicon and CTAB monolayer covering mica surfaces, respectively.
International Journal of …, 2012
The increasing importance of studies on soft matter and their impact on new technologies, including those associated with nanotechnology, has brought intermolecular and surface forces to the forefront of physics and materials science, for these are the prevailing forces in micro and nanosystems. With experimental methods such as the atomic force spectroscopy (AFS), it is now possible to measure these forces accurately, in addition to providing information on local material properties such as elasticity, hardness and adhesion. This review provides the theoretical and experimental background of AFS, adhesion forces, intermolecular interactions and surface forces in air, vacuum and in solution.
Use of atomic force microscope for the measurements of hydrophobic forces
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1994
An atomic force microscope (AFM) was used to measure the short-and long-range hydrophobic attractive forces between a silanated silica plate and a glass sphere. Octadecyltrichlorosilane (ODTCS) and trimethylchlorosilane (TMCS) were used to render the surfaces hydrophobic with advancing contact angles (8,) in the 88-115" range. The forces measured with surfaces coated with TMCS ((1. = 88") are comparable to those obtained previously using the surface force apparatus (SFA). On the other hand, the hydrophobic forces measured with ODTCS-coated surfaces are much larger than those measured with mica surfaces coated with other long-chain surfactants such as dimethyldioctadecylammonium bromide. The long-range hydrophobic force increases sharply at (I, > 95 '. The AFM images show that the surfactants adsorb on the silica surface forming domains (or molecular clusters). With ODTCS. elliptical domains begin to form at relatively low coverages. their size and the distance between them remaining relatively constant with increasing 0.. At the same time, the decay length of the long-range hydrophobic force does not change significantly with U.. while its strength increases sharply at (I, > 95". These findings suggest that the decay lengths of long-range hydrophobic forces vary with the domain size and the distance between them, with their strength increasing with increasing packing density and hence the ordering of the hydrocarbon chains in the domains. The AFM force measurements conducted in the present work also show that the hydrophobic force significantly increases in argon-saturated water, suggesting that the cavitation mechanism may play a role. Only short-range hydrophobic forces have been observed between hydrophilic silica and hydrophobic (silanated) glass. The adhesion forces measured by AFM show a strong dependence on II,, which can be explained by the Young-Dupri equation with appropriate corrections.
Modern Research and Educational Topics in Microscopy, 2007
Atomic force microscopy (AFM) has been useful to investigate materials performance, processes, physical and surface properties at the nanometer scale. In addition to the standard AFM, which measures surface topography, many accessories have been developed to obtain specific additional information. In this chapter, we shall concentrate on atomic force spectroscopy (AFS), which derived from AFM and is used to measure surface forces through force curves. The latter curves have become an important tool to study materials properties, such as elasticity, surface charge densities and wettability. With AFS one probes interactions at the nanometer scale, especially van der Waals interactions and double-layer forces. A brief theoretical background is included, and we comment on the large variety of measurements involving AFS.
Journal of Colloid and Interface Science, 2019
The interface between water and a textured hydrophobic surface can exist in two regimes; either the Wenzel (surface-engulfed) or Cassie-Baxter (water-suspended) state. Better understanding of the influence of pattern geometry and spacing is crucial for the design of functional (super)hydrophobic surfaces, as inspired by numerous examples in nature. In this work, we have employed amplitude modulated-atomic force microscopy to visualize the air-water interface with an unprecedented degree of clarity on a superhydrophobic and a highly hydrophobic nanostructured surface. The images obtained provide the first real-time experimental visualization of the Cassie-Baxter wetting on the surface of biomimetic silicon nanopillars and a naturally superhydrophobic cicada wing. For both surfaces, the air-water interface was found to be remarkably well-defined, revealing a distinctly nanostructured air-water interface in the interstitial spacing. The degree of interfacial texture differed as a function of surface geometry. These results reveal that the air-water interface is heterogeneous in its structure and confirmed the presence of short-range interfacial ordering. Additionally, the overpressure values for each point on the interface were calculated, quantifying the difference in wetting behavior for the biomimetic and natural surface. Results suggest that highly-ordered, closely spaced nanofeatures facilitate robust Cassie-Baxter wetting states and therefore, can enhance the stability of (super)hydrophobic surfaces.
Quantitative Analysis of Fluid Interface–Atomic Force Microscopy
Journal of Colloid and Interface Science, 2001
Net repulsive interactions between n-hexadecane and a polystyrene microsphere in aqueous solutions are measured with atomic force microscopy and interpreted using the augmented Young-Laplace equation. The true separation between probe and fluid interface is implicitly computed from the force-distance data, providing a more accurate description of drop or bubble deformation. Experiments and theoretical arguments demonstrate that a fluid interface stiffens with increasing deformation and is not accurately treated as a Hookean spring. The unexpected stability of the draining aqueous film between hydrophobic bodies in electrolyte solutions is explained primarily by the deformation of the oil drop in response to the applied normal force, as well as the increased hydrodynamic resistance due to the increased drainage area.
Influence of roughness on capillary forces between hydrophilic surfaces
Physical Review E, 2008
Capillary forces have been measured by atomic force microscopy in the plate-sphere setup between gold, borosilicate glass, GeSbTe, titanium, and UV-irradiated amorphous titanium-dioxide surfaces. The force measurements were performed as a function contact time and surface roughness in the range 0.2-15 nm rms and relative humidity ranging between 2% and 40%. It is found that even for the lowest attainable relative humidity ͑ϳ2% Ϯ 1%͒ very large capillary forces are still present. The latter suggests the persistence of a nanometersthick adsorbed water layer that acts as a capillary bridge between contacting surfaces. Moreover, we found a significantly different scaling behavior of the force with rms roughness for materials with different hydrophilicity as compared to gold-gold surfaces.
Adsorption of Water on Solid Surfaces Studied by Scanning Force Microscopy
Langmuir, 2000
Tip-sample interaction of an oscillating tip near a surface is determined. The experimental results show that the presence of the surface can be detected without mechanically touching the surface. By adjusting the appropriate operating conditions of a scanning force microscope setup, tip-sample contact can be avoided during imaging at atmospheric pressure. This allows study of even the softest samples. In the present work, we demonstrate that molecularly thin water films can be imaged with nanometer resolution on different substrates such as mica, gold, and highly oriented pyrolitic graphite. Correspondingly, scanning force microscopy can be used to investigate wetting properties of liquids with very high spatial resolution.