Direct measurement of colloidal forces using an atomic force microscope
TL;DR: In this article, the authors used the atomic force microscope to measure the forces between a planar surface and an individual colloid particle, a silica sphere of radius 3.5 µm, attached to the force sensor in the microscope and measured in solutions of sodium chloride.
Abstract: THE forces between colloidal particles dominate the behaviour of a great variety of materials, including paints, paper, soil, clays and (in some circumstances) cells. Here we describe the use of the atomic force microscope to measure directly the force between a planar surface and an individual colloid particle. The particle, a silica sphere of radius 3.5 µm, was attached to the force sensor in the microscope and the force between the particle and the surface was measured in solutions of sodium chloride. The measurements are consistent with the double-layer theory1,2 of colloidal forces, although at very short distances there are deviations that may be attributed to hydration forces3–6 or surface roughness, and with previous studies on macroscopic systems4–6. Similar measurements should be possible for a wide range of the particulate and fibrous materials that are often encountered in industrial contexts, provided that they can be attached to the microscope probe.
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TL;DR: The atomic force microscope (AFM) is not only used to image the topography of solid surfaces at high resolution but also to measure force-versus-distance curves as discussed by the authors, which provide valuable information on local material properties such as elasticity, hardness, Hamaker constant, adhesion and surface charge densities.
3,281 citations
TL;DR: The spring constant of microfabricated cantilevers used in scanning force microscopy (SFM) can be determined by measuring their resonant frequencies before and after adding small end masses as mentioned in this paper.
Abstract: The spring constant of microfabricated cantilevers used in scanning force microscopy (SFM) can be determined by measuring their resonant frequencies before and after adding small end masses These masses adhere naturally and can be easily removed before using the cantilever for SFM, making the method nondestructive The observed variability in spring constant—almost an order of magnitude for a single type of cantilever—necessitates calibration of individual cantilevers in work where precise knowledge of forces is required Measurements also revealed that the spring constant scales with the cube of the unloaded resonant frequency, providing a simple way to estimate the spring constant for less precise work
1,635 citations
TL;DR: Atomic force microscopy (AFM) force-distance curves have become a fundamental tool in several fields of research, such as surface science, materials engineering, biochemistry and biology.
1,559 citations
TL;DR: An alternative interpretation of why hydrophilic surfaces and macromolecules remain well separated in water is suggested, in which hydration forces are either attractive or oscillatory, and where repulsions have a totally different origin.
Abstract: The conventional explanation of why hydrophilic surfaces and macromolecules remain well separated in water is that they experience a monotonically repulsive hydration force owing to structuring of water molecules at the surfaces. A consideration of recent experimental and theoretical results suggests an alternative interpretation in which hydration forces are either attractive or oscillatory, and where repulsions have a totally different origin. Further experiments are needed to distinguish between these possibilities.
1,225 citations
TL;DR: In this article, a review of colloidal processing of ceramics is presented with an emphasis on interparticle forces, suspension rheology, consolidation techniques, and drying behavior.
Abstract: Colloidal processing of ceramics is reviewed with an emphasis on interparticle forces, suspension rheology, consolidation techniques, and drying behavior. Particular attention is given to the scientific concepts that underpin the fabrication of particulate-derived ceramic components. The complex interplay between suspension stability and its structural evolution during colloidal processing is highlighted.
1,211 citations
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TL;DR: The atomic force microscope as mentioned in this paper is a combination of the principles of the scanning tunneling microscope and the stylus profilometer, which was proposed as a method to measure forces as small as 10-18 N. As one application for this concept, they introduce a new type of microscope capable of investigating surfaces of insulators on an atomic scale.
Abstract: The scanning tunneling microscope is proposed as a method to measure forces as small as 10-18 N. As one application for this concept, we introduce a new type of microscope capable of investigating surfaces of insulators on an atomic scale. The atomic force microscope is a combination of the principles of the scanning tunneling microscope and the stylus profilometer. It incorporates a probe that does not damage the surface. Our preliminary results in air demonstrate a lateral resolution of 30 A and a vertical resolution less than 1 A.
12,344 citations
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19 Mar 1987
TL;DR: The structure of concentrated dispersions thin films Emulsions Microemulsions Rheology of colloidal dispersions and their properties are described in detail in this paper, with a focus on statistical mechanics of fluids.
Abstract: Introduction to statistical mechanics of fluids Adsorption from Solution The electrokinetic effects The structure of concentrated dispersions Thin films Emulsions Microemulsions Rheology of colloidal dispersions.
3,325 citations
TL;DR: Theory of the Stability of Lyophobic Colloids The Interaction of Sol Particles having an Electric Double Layer and the nature of the electrical double layer which exists around them in salt solutions is discovered.
Abstract: MANY of the classical investigations of colloidal chemistry were concerned with the stability of colloidal solutions of insoluble substances, such as gold, arsenic sulphide, silver halides, etc. The well-known phenomenon of coagulation of these sols by comparatively small concentrations of electrolytes suggested that their stability was connected with their electric charges. A considerable amount of research has been made in the past to discover the magnitude and origin of the electric charge on the particles and the nature of the electrical double layer which exists around them in salt solutions. Although qualitative and semi-quantitative explanations have been given of the phenomenon of coagulation and of the rule of Hardy and Schulze, according to which the ionic concentration required for precipitation diminishes rapidly with the charge of the effective ion, yet a complete and satisfactory theory was still lacking. Theory of the Stability of Lyophobic Colloids The Interaction of Sol Particles having an Electric Double Layer. By E. J. W. Verwey and J. Th. G. Overbeek., with the collaboration of K. van Nes. Pp. xi + 205. (New York and Amsterdam : Elsevier Publishing Co., Inc. ; London : Cleaver-Hume Press, Ltd., 1948.) 22s. 6d. net.
3,099 citations