Donald Saul Rimai

Molecular Dynamic Modeling of Particle Adhesion

Abstract Molecular dynamic modeling was used to study the interactions between nanometer size two-dimensional particles in proximity to the surface of a two-dimensional crystal composed of the same material. The modeling was conducted by using triangular lattices of atoms that interact through a Lennard-Jones potential. The atoms were configured such that the particle consisted of a circle with 463 atoms. The crystal was in the shape of a rectangle and contained 442 atoms. The system was assumed to have periodic boundary conditions. It was first allowed to equilibrate with an assumed dimensionless kinetic energy per atom of 0.2 e. Subsequently, the particle was made to approach the surface at a velocity of 0.387 [sgrave]/t (corresponding to 6.25 m/s for argon), which is small compared with the speed of sound in the material. The approach was conducted in two modes: (1) centroidal displacement control at constant temperature and (2) free flight at the same intercentroidal velocity of approach. For each cas...

The adhesion of spherical particles: Contributions of Van Der Waals and electrostatic interactions

The forces needed to detach monodisperse spherical polystyrene particles having radii between approximately 1 μm and 6 μm from a polyester substrate were determined using electrostatic detachment. It was found that the removal force varied linearly with particle radius, as predicted by the JKR theory (K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Soc. London, Ser. A 324 , 301 (1971)). In addition, the work of adhesion, estimated from JKR theory, was found to be approximately 0.01 J/m 2 . This is a reasonable value for a system such as this. These results are, however, inconsistent with the predictions of models that assume that particle adhesion is dominated by electrostatic forces due to either a uniform charge distribution over the surface of the particle or localized charged patches.

Effects of Electrostatic and van der Waals Interactions on the Adhesion of Spherical 7 µm Particles

ABSTRACT The force needed to detach spherical particles having a number average diameter of 7.1 μm from a polymeric, photoconducting substrate was determined by ultracentrifugation. In the absence of any release agents applied to the substrate, it was found that only a small fraction of the particles could be removed from the substrate even at the highest centripetal accelerations (354,000 g). However, when the substrate was coated with a thin layer of a release aid (zinc stearate), the force needed to separate the particles from the substrate was greatly reduced, thereby allowing the detachment force to be determined. Under these conditions, it was found that the release force varied with the square of the particle charge-to-mass ratio. Moreover, it was also found by extrapolation that the detachment force at zero charge, corresponding to the residual van der Waals interactions, was finite. These results suggest that both van der Waals and electrostatic interactions affect the adhesion of particles and, for micrometer-sized particles, electrostatic forces can become dominant under some circumstances. Conversely, the large increase in the adhesion of the particles to the substrate, in the absence of a good release agent, suggests that van der Waals forces would often dominate adhesive interactions of particles in this size range.

Particle adhesion : applications and advances

Preface Biological Applications of Particle Adhesion Concepts 1. A Particle Adhesion Perspective of Metastasis B.J. Love and J.E. Forsten 2. Adhesion of Cancer Cells to Endothelial Monolayers: A Study of Initial Attachment Versus Firm Adhesion M.A. Moss and K.W. Anderson 3. Cell-Cell Adhesion of Erythrocytes F.R. Attenborough and K. Kendall 4. Particle-Induced Phagocytic Cell Responses are Material Dependent: Foreign Body Giant Cells vs Osteoclasts from a Chick Chorloallantoic Membrane Particle-implantation Model L .C. Carter, J.M. Carter, P.A. Nickerson Elastic and Viscoelastic Contributions to Understanding Particle Adhesion 5. The Bodys Response to Deliberate Implants: Phagocytic Cell Responses to Large Substrata Vs Small Particles R. Baier, E. Axelson, A. Meyer, L. Carter, D. Kaplan, G. Picciolo and S. Jahan 6. The Bodys Response to Inadvertant Implants: Respirable Particles in Lung Tissues R. Baier, A. Meyer, D. Glaves-Rapp, E. Axelson, R. Forsberg, M. Kozak and P. Nickerson 7. Measurement of the Adhesion of a Viscoelastic Sphere to a Flat Non-Compliant Substrate M. Reitsma. V.S.J. Craig and S. Briggs 8. Surface Forces and the Adhesive Contact of Axisymmetric Elastic Bodies A.-S. Huguet and E. Barthel 9. Finite Element Modeling of Particle Adhesion: A Surface Energy Formalism D.J. Quesnal and D.S. Rimai 10. Creep Effects in Nanometer-scale Contacts to Viscoelastic Materials: A Status Report W.N. Unerti Particle Surface Interactions that Influence Adhesion 11. Experiments and Engineering Models of Microparticle Impact and Deposition R.M. Brach, P.F. Dunn, and X. Li 12. The Adhesion of Irregularly-Shaped 8 m Diameter Particles to Substrates: The Contributions of Electrostatic and van der Waals interactions D.S. Riami, D.J. Quesnel and Reifenberger Electrical Conductivity Through Particles 13. Copper-based Conductive Polymers: A New Concept in Conductive Resins D.W. Marshall Exploring Particle Adhesion with Single Particle Experiments 14. Interactions Between Micron-sized Glass Particles and Poly (dimethyl siloxane) in the Absence and Presence of Applied Load G. Tolkka, G.M. Spinks and H.R. Brown 15. Atomic Force Microscope Techniques for Adhesion Measurements D.M. Schaefer and J. Gomez 16. Limitation of the Young-Dupre Equation in the Analysis of Adhesion Forces Involving Surfactant Solutions J. Drellch, E. Beech, A. Gosiewska and J.D. Miller 17. Mechanical Detachment of Nanometer Particles Strongly Adhering to a Substrate: An Application of Corrosive Tribology J.T. Dickinson, R.F. Harladi and S.C. Langford Advances in Controlling the Attachement and Removal of Groups of Particles 18. The Effect of Relative Humidity on Particle Adhesion and Removal A.A. Busnaina and T. Elsawy 19. The Effect of Time and Humidity on Particle Adhesion and Removal J.Tang and A.A. Busnaina

Effects of submicrometer particulate silica addenda on the adhesion of micrometer-size particles to a polyester-composite substrate

The force needed to detach five sets of different size particles, having number-averaged diameters between 3.6 and 8.5 µm, from a composite substrate was measured using an ultracentrifuge. In addition to size variations, the asperity concentration for each size particle was adjusted by varying the silica concentration, adjusted so that the surface area concentration at each level was kept constant for the five sizes of particles. Due to the changing silica concentration and particle size, the charge per particle also varied. It was found that the detachment force appeared to be virtually independent of charge, with any correlation actually appearing slightly negative, if anything. However, the detachment force increased monotonically with increasing particle diameter and decreased monotonically with increasing silica concentration. Moreover, upon normalizing the detachment force to the particle diameter and the silica concentration to the surface area concentration of silica, it was found that the detachment force clustered into groups in which the force needed to separate the particle from the substrate depended only on the silica concentration. These results suggest that van der Waals interaction, rather than electrostatic forces, are the dominant mechanism controlling toner adhesion in this instance.

The Adhesion of Irregularly-shaped 8 μm Diameter Particles to Substrates: The Contributions of Electrostatic and van der Waals Interactions

Abstract The forces needed to remove irregularly-shaped, 8 μm diameter, polyester particles from a polyester substrate were measured using an ultracentrifuge. Measurements were also made on a second set of similar particles where nanometer-size silica clusters had been placed on their surfaces. These silica clusters acted as spacers, reducing direct contact between the particle and the substrate. It was found that the separation forces for the bare particles were consistent with predictions of the JKR theory of adhesion, but were much larger than could be accounted for from simple electrostatic interactions associated with either uniformly-charged particles or particles with localized charged patches. It was found, however, that the forces needed to effect separation decreased with increasing silica concentration. For particles with 2% by weight silica clusters on their surfaces, the separation force was only about 5% of the separation forces of the bare particles. At this concentration of silica, the estimates of the separation forces obtained from JKR theory, from the uniformly-charged model, and from the localized-charged-patch model are all about equal. The numerical estimates are consistent with the experimentally-obtained values.

The Time Dependence of the Detachment Force of Ground Micrometer-Size Particles from a Planar Substrate: Effect of Particle Rotation

The time dependence of the detachment force applied to 7 µm ground polyester particles coated with silica nanoparticles was determined by ultracentrifugation. It was found that the force required to separate the particles from the substrate increased during the first 24 hours and changed very little thereafter. Scanning electron microscopy (SEM) results suggest that the increase in adhesion is due to the particles rotating from their initial positions obtained during deposition. The role of the silica nanoparticles in determining the time dependence of the detachment force is discussed in terms of the JKR and Fuller–Tabor models.

Time-Dependence of the Adhesion of Micrometer-Size Particles to Substrates: Correlation with Postdeposition Particle Rotation

The time dependence of the detachment force of 7-µm ground polyester particles coated with silica nanoparticles from a ceramer-coated substrate was determined by ultracentrifugation. The detachment force of the particles from the substrate was found to increase with the time since the particle deposition. Scanning electron microscopy (SEM) results show that, following deposition, the particles rotate at approximately the same scale as the observed increase in the detachment force. This suggests that the increase in adhesion may be due to particle rotation from their initial positions obtained upon deposition to a more stable position that results from torques generated by either electrostatic or van der Waals forces acting on the particles.

Finite Element Modeling of Particle Adhesion: A Surface Energy Formalism

Abstract The adhesion of particles is modeled with finite element analysis using an energy approach comparable with that used in the JKR formalism. The strain energy of a cylindrically symmetric system, comprising a particle adhering to a surface with a fixed contact size, is computed as a function of contact size and then added to an energy term that is linearly proportional to the contact patch area. These computations also include contributions from the potential energy of a body force comparable with that which might be applied by a centrifuge. The results show regions of stability (adhesion) where a local energy minimum exists and regions of release where separation of the particle from the surface leads to a continuous decrease in the energy of the system. The effect of the deformation of the particle is included implicitly as a result of the FEM which provides details of the strains and stresses within the system. Discussion concentrates on the physical meaning of the behaviors and the significance of JKR-like theories that use an effective surface energy to represent electrostatic and van der Waals contributions to the adhesion. Modeling the effects of surface roughness of particles and the plastic deformation of particles through an effective surface energy is considered.