The Experts below are selected from a list of 10101 Experts worldwide ranked by ideXlab platform
Hansjurgen Butt - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic Force between a sphere and a soft elastic surface
Langmuir, 2014Co-Authors: Farzaneh Kaveh, Javed Ally, Michael Kappl, Hansjurgen ButtAbstract:The Hydrodynamic drainage Force between a spherical silica particle and a soft, elastic polydimethylsiloxane surface was measured using the colloidal probe technique. The experimental Force curves were compared to finite element simulations and an analytical model. The Hydrodynamic repulsion decreased when the particle approached the soft surface as compared to a hard substrate. In contrast, when the particle was pulled away from the surface again, the attractive Hydrodynamic Force was increased. The Hydrodynamic attraction increased because the effective area of the narrow gap between sphere and the plane on soft surfaces is larger than on rigid ones.
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influence of the spring constant of cantilevers on Hydrodynamic Force measurements by the colloidal probe technique
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010Co-Authors: Tiago S Rodrigues, Hansjurgen Butt, Elmar BonaccursoAbstract:Abstract There is a substantial disagreement in literature on the interpretation of Hydrodynamic Forces measured with the colloidal probe technique (CPT). While some authors find indications of slip of polar liquids on hydrophilic surfaces (including two of the authors), Honig and Ducker [Phys. Rev. Lett. 98 (2007) 028305] noticed no slip when they used relatively stiff cantilevers. Here, we tested a number of cantilevers with different shapes, dimensions, and spring constants to analyse their influence on Hydrodynamic Force measurements. In accordance with Honig and Ducker, we show that results obtained with the CPT do not contradict the no-slip boundary condition if the experiments are carried out with stiff cantilevers. The slip lengths inferred from the measurements can be related to the cantilever spring constant, the velocity at which the cantilever is dragged through the liquid, and the viscosity of the liquid. An empirical threshold value is suggested that could help avoiding artefacts.
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Hydrodynamic Force measurements boundary slip of water on hydrophilic surfaces and electrokinetic effects
Physical Review Letters, 2002Co-Authors: Elmar Bonaccurso, Michael Kappl, Hansjurgen ButtAbstract:The Hydrodynamic drainage Force of aqueous medium between smooth hydrophilic surfaces was measured with the colloidal probe technique up to shear rates of typically 10 4 s 21 . Measured Force curves were compared to simulations. To reach agreement between experimental and simulated Force curves, the Hydrodynamic Force had to be fitted with a model allowing for boundary slippage. Boundary slip was characterized by a slip length of 8 9 nm. Force measurements with charged surfaces could be simulated taking only Hydrodynamic and electrostatic double-layer Forces into account. The structure and mechanical properties of fluids at solid surfaces is important in many phenomena such as lubrication, adhesion, wetting, colloidal Hydrodynamics, and microfluidics. In fluid mechanics, one usually relies on the assumption that, when liquid flows over a solid surface, the liquid molecules adjacent to the solid are stationary relative to the solid and that the viscosity is equal to the bulk viscosity. Though this might be a good assumption for macroscopic systems, it is questionable at molecular dimensions. Measurements with the surface Forces apparatus (SFA) [1 –3] and computer simulations [4–6] showed that the viscosity of simple liquids can increase by many orders of magnitude, or even undergo a liquid-to-solid transition, when they are confined between solid walls separated only few molecular diameters. Several experiments indicated that also isolated solid surfaces induce a layering in an adjacent liquid and that the mechanical properties of the first molecular layers are different from the bulk properties [7–10]. The change in the mechanical properties can be characterized by the position of the plane of shear. Simple liquids often show a shear plane which is typically 3– 5 molecular diameters away from the solid-liquid
Elmar Bonaccurso - One of the best experts on this subject based on the ideXlab platform.
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influence of the spring constant of cantilevers on Hydrodynamic Force measurements by the colloidal probe technique
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2010Co-Authors: Tiago S Rodrigues, Hansjurgen Butt, Elmar BonaccursoAbstract:Abstract There is a substantial disagreement in literature on the interpretation of Hydrodynamic Forces measured with the colloidal probe technique (CPT). While some authors find indications of slip of polar liquids on hydrophilic surfaces (including two of the authors), Honig and Ducker [Phys. Rev. Lett. 98 (2007) 028305] noticed no slip when they used relatively stiff cantilevers. Here, we tested a number of cantilevers with different shapes, dimensions, and spring constants to analyse their influence on Hydrodynamic Force measurements. In accordance with Honig and Ducker, we show that results obtained with the CPT do not contradict the no-slip boundary condition if the experiments are carried out with stiff cantilevers. The slip lengths inferred from the measurements can be related to the cantilever spring constant, the velocity at which the cantilever is dragged through the liquid, and the viscosity of the liquid. An empirical threshold value is suggested that could help avoiding artefacts.
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Hydrodynamic Force measurements boundary slip of water on hydrophilic surfaces and electrokinetic effects
Physical Review Letters, 2002Co-Authors: Elmar Bonaccurso, Michael Kappl, Hansjurgen ButtAbstract:The Hydrodynamic drainage Force of aqueous medium between smooth hydrophilic surfaces was measured with the colloidal probe technique up to shear rates of typically 10 4 s 21 . Measured Force curves were compared to simulations. To reach agreement between experimental and simulated Force curves, the Hydrodynamic Force had to be fitted with a model allowing for boundary slippage. Boundary slip was characterized by a slip length of 8 9 nm. Force measurements with charged surfaces could be simulated taking only Hydrodynamic and electrostatic double-layer Forces into account. The structure and mechanical properties of fluids at solid surfaces is important in many phenomena such as lubrication, adhesion, wetting, colloidal Hydrodynamics, and microfluidics. In fluid mechanics, one usually relies on the assumption that, when liquid flows over a solid surface, the liquid molecules adjacent to the solid are stationary relative to the solid and that the viscosity is equal to the bulk viscosity. Though this might be a good assumption for macroscopic systems, it is questionable at molecular dimensions. Measurements with the surface Forces apparatus (SFA) [1 –3] and computer simulations [4–6] showed that the viscosity of simple liquids can increase by many orders of magnitude, or even undergo a liquid-to-solid transition, when they are confined between solid walls separated only few molecular diameters. Several experiments indicated that also isolated solid surfaces induce a layering in an adjacent liquid and that the mechanical properties of the first molecular layers are different from the bulk properties [7–10]. The change in the mechanical properties can be characterized by the position of the plane of shear. Simple liquids often show a shear plane which is typically 3– 5 molecular diameters away from the solid-liquid
John F Brady - One of the best experts on this subject based on the ideXlab platform.
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the temporal behaviour of the Hydrodynamic Force on a body in response to an abrupt change in velocity at small but finite reynolds number
Journal of Fluid Mechanics, 1995Co-Authors: Phillip M Lovalenti, John F BradyAbstract:A modification to the O(Re)-accurate expression for the Hydrodynamic Force acting on a body in arbitrary time-dependent motion, determined by Lovalenti & Brady (1993), is presented. This simple modification captures the O(Re^2) transient behaviour of the Force, which has been recently shown to dominate at large time (Lawrence & Mei 1995), while maintaining the overall O(Re) accuracy.
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the Hydrodynamic Force on a rigid particle undergoing arbitrary time dependent motion at small reynolds number
Journal of Fluid Mechanics, 1993Co-Authors: Phillip M Lovalenti, John F BradyAbstract:The Hydrodynamic Force acting on a rigid spherical particle translating with arbitrary time-dependent motion in a time-dependent flowing fluid is calculated to O(Re) for small but finite values of the Reynolds number, Re, based on the particle's slip velocity relative to the uniform flow. The corresponding expression for an arbitrarily shaped rigid particle is evaluated for the case when the timescale of variation of the particle's slip velocity is much greater than the diffusive scale, a^2/v, where a is the characteristic particle dimension and v is the kinematic viscosity of the fluid. It is found that the expression for the Hydrodynamic Force is not simply an additive combination of the results from unsteady Stokes flow and steady Oseen flow and that the temporal decay to steady state for small but finite Re is always faster than the t^-½ behaviour of unsteady Stokes flow. For example, when the particle accelerates from rest the temporal approach to steady state scales as t^-2.
Michael Kappl - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic Force between a sphere and a soft elastic surface
Langmuir, 2014Co-Authors: Farzaneh Kaveh, Javed Ally, Michael Kappl, Hansjurgen ButtAbstract:The Hydrodynamic drainage Force between a spherical silica particle and a soft, elastic polydimethylsiloxane surface was measured using the colloidal probe technique. The experimental Force curves were compared to finite element simulations and an analytical model. The Hydrodynamic repulsion decreased when the particle approached the soft surface as compared to a hard substrate. In contrast, when the particle was pulled away from the surface again, the attractive Hydrodynamic Force was increased. The Hydrodynamic attraction increased because the effective area of the narrow gap between sphere and the plane on soft surfaces is larger than on rigid ones.
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Hydrodynamic Force measurements boundary slip of water on hydrophilic surfaces and electrokinetic effects
Physical Review Letters, 2002Co-Authors: Elmar Bonaccurso, Michael Kappl, Hansjurgen ButtAbstract:The Hydrodynamic drainage Force of aqueous medium between smooth hydrophilic surfaces was measured with the colloidal probe technique up to shear rates of typically 10 4 s 21 . Measured Force curves were compared to simulations. To reach agreement between experimental and simulated Force curves, the Hydrodynamic Force had to be fitted with a model allowing for boundary slippage. Boundary slip was characterized by a slip length of 8 9 nm. Force measurements with charged surfaces could be simulated taking only Hydrodynamic and electrostatic double-layer Forces into account. The structure and mechanical properties of fluids at solid surfaces is important in many phenomena such as lubrication, adhesion, wetting, colloidal Hydrodynamics, and microfluidics. In fluid mechanics, one usually relies on the assumption that, when liquid flows over a solid surface, the liquid molecules adjacent to the solid are stationary relative to the solid and that the viscosity is equal to the bulk viscosity. Though this might be a good assumption for macroscopic systems, it is questionable at molecular dimensions. Measurements with the surface Forces apparatus (SFA) [1 –3] and computer simulations [4–6] showed that the viscosity of simple liquids can increase by many orders of magnitude, or even undergo a liquid-to-solid transition, when they are confined between solid walls separated only few molecular diameters. Several experiments indicated that also isolated solid surfaces induce a layering in an adjacent liquid and that the mechanical properties of the first molecular layers are different from the bulk properties [7–10]. The change in the mechanical properties can be characterized by the position of the plane of shear. Simple liquids often show a shear plane which is typically 3– 5 molecular diameters away from the solid-liquid
Phillip M Lovalenti - One of the best experts on this subject based on the ideXlab platform.
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the temporal behaviour of the Hydrodynamic Force on a body in response to an abrupt change in velocity at small but finite reynolds number
Journal of Fluid Mechanics, 1995Co-Authors: Phillip M Lovalenti, John F BradyAbstract:A modification to the O(Re)-accurate expression for the Hydrodynamic Force acting on a body in arbitrary time-dependent motion, determined by Lovalenti & Brady (1993), is presented. This simple modification captures the O(Re^2) transient behaviour of the Force, which has been recently shown to dominate at large time (Lawrence & Mei 1995), while maintaining the overall O(Re) accuracy.
-
the Hydrodynamic Force on a rigid particle undergoing arbitrary time dependent motion at small reynolds number
Journal of Fluid Mechanics, 1993Co-Authors: Phillip M Lovalenti, John F BradyAbstract:The Hydrodynamic Force acting on a rigid spherical particle translating with arbitrary time-dependent motion in a time-dependent flowing fluid is calculated to O(Re) for small but finite values of the Reynolds number, Re, based on the particle's slip velocity relative to the uniform flow. The corresponding expression for an arbitrarily shaped rigid particle is evaluated for the case when the timescale of variation of the particle's slip velocity is much greater than the diffusive scale, a^2/v, where a is the characteristic particle dimension and v is the kinematic viscosity of the fluid. It is found that the expression for the Hydrodynamic Force is not simply an additive combination of the results from unsteady Stokes flow and steady Oseen flow and that the temporal decay to steady state for small but finite Re is always faster than the t^-½ behaviour of unsteady Stokes flow. For example, when the particle accelerates from rest the temporal approach to steady state scales as t^-2.