Use of the light-lever technique for the measurement of colloidal forces (original) (raw)
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Application of the Light-Lever Technique to the Study of Colloidal Forces
Langmuir, 1996
Force measurements in a variety of colloidal systems have been conducted using a new device which utilizes the light-lever technique employed in atomic force microscopy. The systems studied include electrostatic double-layer forces, hydrophobic interactions, liquid crystal structures, and polymer adsorption forces. The new device has some clear advantages over adaptation of an imaging atomic force microscope for force measurements.
Langmuir, 2009
The well-established atomic force microscopy (AFM)-based colloidal probe technique (CPT) and optical tweezers (OT) are combined to measure the interaction forces between blank SiO 2 surfaces in aqueous ionic solutions (CaCl 2 ) of varying concentration at pH 7. Spherical colloids (SiO 2 , diameter ∼ 4.63 ( 0.05 μm) taken out of the same batch are used by both methods. In the case of CPT, a single colloid is glued to a cantilever, and the interaction forces with a plain SiO 2 surface are determined in dependence on the concentration of the surrounding medium. For the OT studies, two colloids (one fixed to a micropipet by capillary action, the other held with the optical trap) are approached to each other in nanometer steps, and the resulting forces are measured for the same media as in the CPT experiment. Both techniques fit well to each other and enable one to cover interaction energies ranging from 10 -5 to 1 mN/m. The experimental data are well described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory revealing that the effective surface charge density changes slightly with concentration.
Journal of Colloid and Interface Science, 2006
Colloidal forces between atomic force microscopy probes of 0.12 and 0.58 N/m spring constant and flat substrates in nanoparticle suspensions were measured. Silicon nitride tips and glass spheres with a diameter of 5 and 15 µm were used as the probes whereas mica and silicon wafer were used as substrates. Aqueous suspensions were made of 5-80 nm alumina and 10 nm silica particles. Oscillatory force profiles were obtained using atomic force microscope. This finding indicates that the nanoparticles remain to be stratified in the intervening liquid films between the probe and substrate during the force measurements. Such structural effects were manifested for systems featuring attractive and weak repulsive interactions of nanoparticles with the probe and substrate. Oscillation of the structural forces shows a periodicity close to the size of nanoparticles in the suspension. When the nanoparticles are oppositely charged to the probes, they tend to coat the probes and hinder probe-substrate contact.
Atomic force microscopy and direct surface force measurements (IUPAC Technical Report
Pure and Applied Chemistry, 2005
Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment, with full reference to the source, along with use of the copyright symbol ©, the name IUPAC, and the year of publication, are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.
Atomic force microscopy and direct surface force measurements
Pure and Applied Chemistry, 2005
Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment, with full reference to the source, along with use of the copyright symbol ©, the name IUPAC, and the year of publication, are prominently visible. Publication of a translation into another language is subject to the additional condition of prior approval from the relevant IUPAC National Adhering Organization.
The measurements of colloidal forces between an AFM probe and nanoparticles deposited on a substrate
We report structural forces measured for 10 nm silica particles deposited on alumina substrate and 5-80 nm alumina particles on mica using atomic force microscopy technique. For nanoparticles forming clusters, oscillation of structural forces was recorded with a periodicity that is close to the size of the nanoparticles used. Additionally, selected force-separation results indicate that the forces involved between the AFM probe and individual nanoparticles can be studied using the nanoparticle-coated substrates.
Interaction forces between colloidal particles in liquid: Theory and experiment
Advances in Colloid and Interface Science, 2007
The interaction forces acting between colloidal particles in suspensions play an important part in determining the properties of a variety of materials, the behaviour of a range of industrial and environmental processes. Below we briefly review the theories of the colloidal forces between particles and surfaces including London-van der Waals forces, electrical double layer forces, solvation forces, hydrophobic forces and steric forces. In the framework of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, theoretical predictions of total interparticle interaction forces are discussed. A survey of direct measurements of the interaction forces between colloidal particles as a function of the surface separation is presented. Most of the measurements have been carried out mainly using the atomic force microscopy (AFM) as well as the surface force apparatus (SFA) in the liquid phase. With the highly sophisticated and versatile techniques that are employed by far, the existing interaction theories between surfaces have been validated and advanced. In addition, the direct force measurements by AFM have also been useful in the explaining or understanding of more complex phenomena and in engineering the products and processes occurring in many industrial applications.
Non-destructive force measurement in liquid using atomic force microscope
Applied Surface Science, 2002
Atomic force microscopy (AFM) has been applied to measure inter-or intra-molecular forces acting to hold biological molecules and structures. For these measurements, it is important to keep the target molecules biologically active on a solid surface. Besides the strategy for immobilizing them on the surface keeping their biological activities intact, it is crucial to reduce the force applied to them through the AFM tip to avoid mechanical inactivation of the sample. In this paper, we propose a new procedure to minimize the effect of contact force. The first step of the procedure is to bring the cantilever tip close to the sample surface within less than 3 mm, but short of contact with the sample surface. The approximate distance of the tip from the sample stage is measured using the thermal fluctuation of the cantilever. The second step is a ''compression-free'' force spectroscopy for the measurement of protein-protein interactions only, which is possible when the piezo scanner was retracted before the cantilever starts upward deflection. The interaction force can be measured in the retraction period provided a physical contact is established between the proteins on the tip and the substrate. This procedure allowed to measure interaction forces between GroEL and a denatured protein without mechanical deformation. #
Measuring forces with the AFM: polymeric surfaces in liquids
Advances in Colloid and Interface Science, 2002
This review links together for the first time both the practicalities of force measurement and the work carried out to date on force detection between polymeric surfaces in liquids Ž . using the atomic force microscope AFM . Also included is some of the recent work that has been carried out between surfactant surfaces and biologically coated surfaces with the AFM. The emphasis in this review is on the practical issues involved with force measurement between these types of surfaces, and the similarities and irregularities between the observed types of forces measured. Comparison is made between AFM and surface force apparatus Ž . SFA measurements, as there is a much longer history of work with the latter. Results indicate that forces between the surfaces reviewed here are a complicated mixture of steric-type repulsion, conformational behaviour on separation and long-range attraction, which is often ascribed to 'hydrophobic' forces. The origin of this latter force remains uncertain, despite its almost ubiquitous appearance in force measurements with these types of surfaces. ᮊ
Langmuir, 1997
Measurements are made of the forces acting on the tip of an atomic force microscope when the sample and cantilever are in air and also immersed in polar solvents like water and DMSO. For large tip/substrate separations (>1000 nm) the liquid drag force can be modeled using a classical hydrodynamic drag force expression. For separations between the tip and substrate smaller than around 100 nm in a water medium, the force due to the effective viscosity increase of the compressed films for high tip/substrate relative velocity is comparable to the contribution of the double-layer repulsion and the van der Waals attraction. After tip/substrate contact these compressed films produce an attractive force that is a function of the liquid medium. In the DMSO medium the attractive force between tip and substrate shows an adhesive force that has at least two components indicating a multilayered structure between the tip and substrate during the tip/substrate separation. The scanning of a surface immersed in water and DMSO with a tip "in contact" produces distinct AFM images which depend on the liquid. These images show diverse symmetries and spacings between features which presumably correspond to the solvated atomic structure and are only obtained with atomic resolution for a scanning speed of ∼2 nm/s. It is possible to estimate the viscous relaxation time of the compressed layer value to be ∼250 ms from the observed resolution of substrate structures as a function of scanning speed.