Donald S. Rimai

Surface roughness and its influence on particle adhesion using atomic force techniques

The surface force interactions between individual 8 μm diameter spheres and atomically flat substrates have been investigated using atomic force techniques. The lift-off force of glass, polystyrene, and tin particles from atomically smooth mica and highly oriented pyrolitic graphite substrates was determined as a function of the applied loading force in an inert nitrogen environment. While the relative magnitudes of the measured lift-off force were found to scale as expected between the various systems studied, the absolute values were a factor of ∼50 smaller than expected from the Johnson, Kendall, and Roberts theory. The surface topography of representative spheres was characterized with atomic force microscopy, allowing a quantitative assessment of the role that surface roughness plays in the adhesion of micrometer-size particles to substrates. Taking into account the radius of curvature of the asperities measured from the atomic force scans, agreement between the measured and theoretical estimates for...

Mechanics of particle adhesion

The adhesion of particles to surfaces is accompanied by deformations of the materials arising from adhesion force-induced stresses. These deformations, which can be the result of an elastic, a nonlinear elastic, a viscoelastic, or a plastic response of the materials to the stresses, can significantly affect the forces needed to remove the particles from the substrate. The mechanics of adhesion-induced deformations between micrometer-size particles and various substrates are discussed in this paper. Examples of elastic and plastic deformations resulting from the adhesion forces are presented. The experimental results are analyzed in terms of various adhesion theories, which, under certain circumstances, permit the calculation of the thermodynamic work of adhesion for contacting solids. The ranges of validity of these theories and their predictions are discussed. Finally, adhesion-induced deformations which are not currently explicable in terms of these theories are presented.

Surface-force-induced deformations of monodisperse polystyrene spheres on planar silicon substrates

The contact radii between polystyrene spheres, having diameters between approximately 1.5 and 12 μm, and polished silicon wafers, arising from adhesion forces, were determined using scanning electron microscopy. It was found that the contact radius varied approximately as the square root of the particle radius. This dependence is consistent with nonelastic response models of adhesion, such as those proposed by Krupp [H. Krupp, Adv. Colloid Interface Sci. 1, 111 (1967)] and by Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984)], but is inconsistent with various elastic response models which assume Hertzian deformations. The experimentally determined contact radii are also compared to those obtained for polystyrene spheres on a polyurethane substrate [D. S. Rimai, L. P. DeMejo, and R. C. Bowen, J. Appl. Phys. 66, 3574 (1989)].

Surface force interactions between micrometer-size polystyrene spheres and silicon substrates using atomic force techniques

The surface force interactions between a single micrometer-size polystyrene sphere and a p-type silicon substrate were investigated using atomic force microscope techniques. The force of removal and the degree of deformation of the particle determined as a function of the applied loading force. The work of removal, estimated assuming a perfectly spherical particle and a smooth substrate, was also determined. The influence of surface contamination and the implications of the short contact times used in these experiments are discussed.

Adhesion‐induced deformations of polymeric substrates: Particle size dependence of the contact area

Adhesion‐induced deformations of a polyurethane substrate in contact with cross‐linked polystyrene spheres, having diameters ranging from less than 2 μm to approximately 12.5 μm were observed using scanning electron microscopy. The diameters of the contact areas were measured from the micrographs. It was found that the contact radius varied as the particle radius raised to the 0.75±0.05 power. Experimental results are compared to the predictions of various adhesion models. The results are also discussed in terms of the Dupre work of adhesion.

Adhesion-induced deformations of polyurethane substrates in contact with spherical glass particles : the effect of particle size on the radius of contact

Spherical glass particles having radii between approximately 0.5 and 100 *m were deposited onto a polyurethane substrate and the radii of contact, resulting from the adhesion forces between the particles and the substrate, were determined using SEM. For particles having radii less than approximately 5 μm, it was found that the contact radius varied as the particle radius to the 0.75 power. In addition, large menisci, presumably resulting from tensile interations, were observed. For particles having radii between 5 and 60 μm, the contact radius varied as the particle raidus to the 2/3 power. Stretching of the substrate was also observed for particles having radii of approximately 100 μm. This is probably a harbinger of the impending separation of the particle from the substrate, due to gravitational forces. The thermodynamic work of adhesion was calculated from the data and the results were compared with the predictions of several theories of particle adhesion.

The Interaction between Micrometer-size Particles and Flat Substrates: A Quantitative Study of Jump-to-Contact

Abstract The interaction force acting on an individual micrometer-size polystyrene particle near a flat, electrically conducting substrate has been measured by attaching the particle to an atomic force microscope cantilever. From the spatial dependence of the interaction force, the equations of motion governing a particle near the substrate can be determined. These considerations allow a prediction of the jump-to-contact distance of the particle as it approaches the substrate. This distance is measured as a function of particle radius and compared with predictions based on the relevant interaction force models.

Direct observations of deformations resulting from particle-substrate adhesion

Deformations of planar substrates and contacting particles due to surface forces, such as the van der Waals interactions, were postulated long ago. Direct observations of such deformations between submicrometer Kynar 301 F™ particles and substrates consisting of polyester-siloxane block copolymers or polished silicon, obtained using scanning electron microscopy (SEM), are presented. The deformations observed in the polyester-siloxane substrate are too large to be explained using Hertzian theory of elastic behavior but are consistent with the plastic deformation model of Krupp and the tensile model of Johnson et al. Potential experimental artifacts, such as space charge effects and the effect of using conducting coatings, are discussed.

Observations of adhesion-induced deformations between spheroidal gold particles and conducting substrates

Spheroidal gold particles, approximately 3 μm in diameter, were deposited on both hard and soft planar, electrically conducting substrates, and the interfaces were observed using scanning electron microscopy. It was observed that the particles appeared to embed into the softer substrate, but not into the harder one. The softer substrate also appeared to flow up the sides of the particles. The diameters of the craters formed are compared with the predictions based on Hertz’ [Zimon, Adhesion of Dusts and Powders (Consultants Bureau, New York, 1982)] model of elastic deformation, Krupp’s [Adv. Colloid Interface Sci. 1, 111 (1967)] model of plastic response [assuming van der Waals (Zimon, ibid. and Krupp, ibid.) interactions], and Johnson, Kendall, and Roberts’ [Proc. R. Soc. London Ser. A 324, 301 (1971)] model of tensile response due to surface tension. These calculations suggest that the observed deformation on the softer substrate is predominantly plastic rather than elastic and that surface tension is si...

Particle adhesion and removal in electrophotography

Particle adhesion and removal is often controlled by the interplay of electrostatic forces, related to electrical charges on the particles, and electrodynamic forces, such as those arising from van der Waals interactions. In addition, when electrostatically detaching a charged particle from a substrate, the manner in which the electric field is applied can alter the charge on the particle, thus changing both the attractive and detachment forces. The effects are clearly illustrated in the transfer of a toned image from the photoconductor in an electrophotographic engine. This paper reviews present day understanding of the interplay between electrostatic and electrodynamic interactions, as they occur within the electrophotographic process, and presents the results of previous studies in a unified manner.