Search results for "Surface force"
showing 10 items of 31 documents
Preliminary results on the electrostatic double-layer force between two surfaces with high surface potentials
1998
Abstract The aim of this study is to measure interaction forces between surfaces with high electric potentials in aqueous electrolyte solutions. Therefore the force between a gold sample and a gold sphere attached to the end of an atomic force microscope cantilever was measured. Gold sample and sphere were electrically connected and served as the working electrode. A potential was applied via a platinized platinum electrode. Experimental results are compared to forces approximated with the Poisson-Boltzmann theory.
The role of the hydrophobic force in bilayer adhesion and fusion
1991
The Surface Forces Apparatus technique was used for measuring the adhesion, deformation, and fusion of bilayers supported on mica. The technique allows the molecular rearrangements to be followed in real time during the fusion process, and the most important forces involved to be identified. The adhesion between two bilayers can be increased by two orders of magnitude if they are thinned so as to expose more hydrophobic groups. For all the bilayer systems studied a single basic fusion mechanism was found in which the bilayers do not “overcome” the short-range repulsive steric-hydration forces; instead, local bilayer deformations allow these repulsive forces to be “bypassed”. The results fur…
Investigations of Surface Forces between Gypsum Microcrystals in Air Using Atomic Force Microscopy
2000
This article introduces a new approach to the study of the interactions between gypsum faces in air. We have mounted a gypsum crystal on the end of a microcantilever to measure local forces (van der Waals, capillary forces, electrostatic) directly between two crystals. A systematic study with respect to the orientation of crystalline faces, relative humidity, and the duration of contact between crystals improves the understanding of the mechanism involved in the hardening of plaster in air. In dry air, a physicochemical process of matter transfer is added to the van der Waals forces to ensure the cohesion. Others force measurements were performed by varying the shape of the contact (interac…
Slippage of water over hydrophobic surfaces
1999
When water is confined between hydrophobic surfaces, its flow properties are significantly different from those in bulk, or between hydrophilic surfaces. These changes (that are usually ignored) may be interpreted in terms of hydrophobic slippage. This chapter reviews recent developments in the hydrodynamics of water confined between solid hydrophobic surfaces, emphasizing the main experimental facts, theoretical models suggested, and different aspects of thin film drainage. The relevance of slippage in hydrophobic surface force measurements and on the coagulation rate of hydrophobic particles is discussed.
Measuring electrostatic double-layer forces on HOPG at high surface potentials
1999
Abstract The aim of this study was to investigate surface forces in aqueous electrolyte solutions between surfaces with high electric potentials. Therefore the force between a surface of highly oriented pyrolytic graphite (HOPG) and a silicon nitride tip of an atomic force microscope was measured. Various electric potentials by a counter electrode were applied to the HOPG, which served as working electrode. As predicted by the Poisson–Boltzmann theory the electrostatic double-layer force changed only in a narrow potential range of ≈300 mV. At high negative sample potentials, where the negatively charged tip was repelled from the sample, the force saturated. At positive potentials an attract…
The Joining of LiNbO3, Quartz, TlBr-TlI and Other Optical Materials by the Use of Thin Metal Films as Bonding Agents
2000
A method of joining ferroelectric, optical and other non-metallic materials, such as lithium niobate, quartz, TlBr-TlI, glass, etc., at room temperature under a pressure of 0.1÷0.5 MPa is described. The surfaces to be joined are prepared to optical flatness, and indium or lead coatings as bonding agents are used. To obtain clean surfaces, procedures of the coating deposition and sample joining are performed in situ in a vacuum of l0-4 Pa. The strength of the obtained joints is about 20MPa for indium coatings and about 30MPa for lead coatings. It is supposed that attractive surface forces play a decisive role in the contact formation and bonding of the wafers. The method has been applied for…
Microsphere tensiometry to measure advancing and receding contact angles on individual particles
1999
In this paper, a method to measure the advancing and receding contact angles on individual colloidal spheres is described. For this purpose, the microspheres were attached to atomic force microscope cantilevers. Then the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble was measured. From these distances the contact angles were calculated. To test the method, experiments were done with silanized silica spheres (4.1 μm in diameter). From the experiments with drops, an advancing contact angle of 101 ± 4° was determined. A receding contact angle of 101 ± 2° was calculated from the jump-in distance into a bubble. Both ex…
Theory and Simulations of Friction between Flat Surfaces Lubricated by Submonolayers
2001
Recent simulations suggest that wearless friction between two solid surfaces can only be obtained if the two surfaces are commensurate or if they are lubricated by a film. Some simple theoretical arguments are given why the presence of a submonolayer film between two solids leads to friction. Possible implications of the symmetry of the confining walls on the tribological properties of the system are then investigated in the presence of a thin film by means of molecular dynamics simulation. Erratic stick-slip motion of the incommensurate system and oscillating friction forces for the commensurate system in the sliding regime are observed.
A thin absorbing layer at the center of a Fabry-Pérot interferometer
1994
The influence of a dye (Rhodamin B) dissolved in solution or adsorbed at an interface at the center of a Fabry-Perot interferometer on the transmission was investigated both experimentally and theoretically. We show that (i) spectra of extremely thin films are measurable at sub-monolayer concentration (one monolayer reduces the transmission by ≃50%), (ii) the transmission is sensitive to the location of an extremely thin film within nm range and (iii) the absorption coefficient is determined quantitatively by comparison between theory and experiment thus permitting one to estimate the local concentration. The results are relevant for the use of dye probes to monitor changes of organic inter…
Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus
2019
Preprint of the open access article Weiss, H., Cheng, H.-W., Mars, J., Li, H., Merola, C., Renner, F. U., Honkimäki, V., Valtiner, M., & Mezger, M. (2019). Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus. Langmuir, 35(51), 16679–16692. https://doi.org/10.1021/acs.langmuir.9b01215