Shear-induced migration and clustering mechanisms of kaolinite clay particles under the oscillating face seal by Jinchul Hong
The migration and clustering mechanisms of clay particles under the contact band of an oscillating face seal are investigated. There are two seperate stages in the wear, which are called the break-in period and the aggressive wear period. First small particles in the slurry penetrate through a short distance under the seal lip, where a thin oil film is present and there is no sign of significant wear. This period is called breakin period. However, after a number of cycles, the particles aggregate and start to form clusters. These clusters grow and the seal wears rapidly. Thus cluster formation plays a critical role in the whole wear process. As a first step, we have compared the possible forces which drive particles inwards. These include the effects of Van der Waals interactions, hydrodynamic shear, Brownian diffusion, etc. In the initial stages of the process, when the particle concentration is not high, prior experiments are consistent with shear-induced migration as the primary mechanism. Particles migrate inwards due to gradients in concentration, shear rate, viscosity and the effects of curved-streamline. Van der Waals force are likely to be dominant when the concentration is high enough so that the distance between the particles is small. In order to confirm these mechanisms, a new experiment using steel seals was carried out and corroborates earlier studies. Finally, some clustering and dispersion mechanisms such as the effects of dissolved ions (leading to aggregation) and thermal expansion of the seal lip (leading to dispersion) were also studied. Thesis Supervisor: L.Mahadevan Title: Associate Professor
Influence of Retardation on the London–van der Waals Forces
IN the course of his work on the stability of colloidal solutions, in which the attraction between the particles is ascribed exclusively to London–van der Waals forces, the repulsion being due to the interaction of electric double layers, Overbeek arrived at the conclusion that in order to account for the stability of suspensions of comparatively large particles, it is necessary to assume that for long distances the London–van der Waals energy decreases more rapidly than R−6; and he pointed out that as soon as the distance becomes comparable to the wave-length corresponding to the excitation energies of the interacting atoms, the retardation of the electrostatic interaction between these atoms can no longer be neglected and will presumably lead to a decrease of the attractive force. Following Overbeek's suggestion, we have studied in detail the influence of retardation on the mutual attraction of two neutral atoms. As is well known, the usual expression for the London force is found by calculating the second order perturbation energy due to the interaction: where q1 and q2 are the operators of the total dipole moments of the two atoms. Since ΔV is proportional to e2, the London interaction is proportional to e4. In order to account for retardation effects, it is necessary also to consider the interaction with the radiation field, and since in this case the interaction operator is proportional to e, the perturbation method must be applied to the fourth order. Although several artifices are required to make the calculation feasible and to avoid divergences, the usual formulation of quantum electrodynamics leads to an unambiguous result.
Degradable polymers : principles and applications
1. Why Biodegradable Polymers? G. Scott. 2. An Overview of Biodegradable Polymers and Biodegradation of Polymers S.H. Huang. 3. Degradation and Stabilization of Carbon-Chain Polymers G. Scott. 4. Techniques and Methods of Polymer Degradation S. Karlsson, A.-C. Albertsson. 5. Biodegradation of Aliphatic Polyesters Suming Li, M. Vert. 6. Starch-Polymer Composites C. Bastioli. 7. Polymers from Renewable Sources E. Chiellini, et al. 8. Sustainable Poly(Hydroxyalkanoate) (PHA) Production G. Braunegg. 9. Polyhydroxyalkanoates: Properties and Modification for High Volume Application I. Chodak. 10. Biodegradable Polymers in Medicine E Piskin. 11. Environmentally Biodegradable Water-Soluble Polymers G. Swift. 12. Plastics and the Environment J. Guillet. 13. Degradable Hydrocarbon Polymers in Waste and Litter Control G. Scott, D.M. Wiles. Subject Index.