Interaction Forces between Two Hard Surfaces in Particle-Containing Aqueous Systems

Abstract

The interaction forces between two hard surfaces in the presence of particle-containing aqueous systems were measured with an atomic force microscope. Bare silica and sodium dodecyl sulfate (SDS)-modified paraffin were used for the surfaces. SDS micelles and colloidal silica were used for the particles. Increasing the number of micelles between two silica surfaces increased the number and magnitude of the oscillations. The effect of the compression speed was seen only with fast speeds g3420 nm s -1 , probably because of a hydrodynamic force. The decay length of the observed electrostatic repulsion decreased with a SDS concentration increase, as a result of an increase in the number of free ions above the critical micelle concentration resulting from a finite dissociation of ions from the surfactant. The effect of using a silica particle instead of a micelle did not show any measurable differences in the oscillations of the force curves. The effect of using an asymmetric system (silica-solution-SDS-modified paraffin) instead of a symmetric system (silica-solution-silica) showed differences only in the Derjaguin-Landau-Verway-Overbeek forces. In all cases, the forces could be explained well by a summation of an electrostatic, van der Waals, and a structural force.

AFM colloidal forces measured between microscopic probes and flat substrates in nanoparticle suspensions

“…(F is the force, D is the separation, and R is the probe radius) than what we could expect for the glass-water-silicon (∼4.7 × 10 −21 J by our estimate, and 1.2 × 10 −20 J for silica-watersilica provided by McNamee et al [8]) is needed to overcome the repulsive forces at 5 nm separation. We also considered the depletion interactions as a source of the step at ∼5 nm in Fig.…”

“…Little work has been reported on force measurements with colloidal probes in solid nanoparticle suspensions using the AFM technique. McNamee et al [8] showed one set of force measurements between two silica surfaces in concentrated suspensions of 10 nm silica particles. However, their experiments were conducted with silica particles of a relatively high surface charge density.…”

Selected Topics of Computational and Experimental Fluid Mechanics

“…Different mechanisms of adsorption affecting the global stability of a colloidal dispersion, including surface-modifying polymer chains versus end-grafted polymer chains, have been studied in [5]. Attempts to measure the forces themselves that act in a confined complex fluid in thermodynamic equilibrium with its surroundings have been made using atomic force microscopy (cf., e.g., [6]), while it has been argued [7] that it is more appropriate to use the concept of disjoining pressure, which is the difference between the 1 force (per colloidal particle unit area) normal to the conning surfaces and the fluids bulk pressure. This disjoining pressure allows for a direct determination of the free energy of interaction, hence its importance.…”

“…The approximation being made is to consider the potential V (r) to be constant during the time step δt which, if taken very small, can make the error negligible. Typical choices for the force field are the electrostatic interaction V (r) = k q q /r and a Lennard-Jones type potential V (r) = 4ε (σ/r) 12 − (σ/r) 6 , where the adjustable parameters (ε, σ, k) must be obtained by other means (first principles or experimentation). Relevant quantities of the system are computed as time-averages over a macroscopic time interval…”

Investigation of stabilization mechanisms for colloidal suspension using nanoparticles.

“…177 The interaction forces between two hard surfaces in sodium dodecyl sulfate containing aqueous systems have also been studied by CP-AFM. 178 Subsequently, Drelich and co-workers have measured the colloidal surface forces between different surfaces in alumina/silica nanoparticle suspensions. 179,180 Because the CP-AFM technique provides an easy and accurate method to qualify the interaction force between colloidal surfaces in both electrolyte and nanoparticle solutions, it is used to investigate the nanoparticle-haloing system in our work.…”