Adhesion of Fine Particles at Solid/Solution Interfaces
- PDF / 801,500 Bytes
- 7 Pages / 604.8 x 806.4 pts Page_size
- 49 Downloads / 172 Views
TIN/JANUARY1990
kinetics of déposition and detachment of small colloid particles in liquid média. Studies of adhésion phenomena are of interest in several fields of technology, biology, medicine, agriculture, and ecology. One of the most significant applications is in particle séparations; e.g., it is relatively simple to remove suspended particles from a liquid by deep bed filtration. A more important, but also a more involved, problem is the séparation of unlike particles from a mixture. Again, sélective adhésion may be employed; it is possible, in principle, to adjust conditions so that one kind of particle attaches to a solid substance, while the other kind remains suspended in the liquid. The selectivity dépends on the surface properties of ail interacting surfaces, such as their electrokinetic p o t e n t i a l (which is d e t e r m i n e d by adsorption affinities of potential determining or other specifically adsorbing ions), or on the spécifie chemical bond formation. Several reviews describe adhésion and related phenomena, 2 " 5 some treating spécial cases, such as binding of biological cells.6 Récent developments in adhésion are addressed in a spécial issue of Colloids and Surfaces7 t h a t c o n t a i n s papers presented at the Symposium on "Particle Déposition at Solid-Liquid Interface" (London, 1988). Adhérence A particle adhères to a solid surface if mutual attraction prevails. When adsorbed, such a particle is located in a minimum of the total interaction energy function (zéro force). As a resuit, an
attractive force will be felt if the particle moves away from the surface, while repulsion occurs if it tends to approach the surface more closely. The energy minimum requires the contributions of short-range repulsion and long-range attraction forces. While the latter are due to van der Waals-London interaction (dispersion force) (see Figure la), short-range repulsion forces are less well u n d e r s t o o d . It has been established, that under certain conditions, adhered particles may detach spontaneously. In other Systems, they either do not deposit on the surface, or do so very slowly. To explain thèse findings, one needs to consider long-range repulsion forces, which are electrostatic in nature (Figure l b ) . I n d e e d , spontaneous particle detachment may take place only if the particles and the surface bear the charge of the same sign. When the charge on the particle and the surface is of opposite sign, the electrostatic attraction produces a deep energy minimum and, consequently, strong adhérence (Figure le). Thèse three contributions to the total interaction energy are the basis of the classic D e r y a g i n - L a n d a u - V e r v e y Overbeek (DLVO) theory and can semiquantitatively explain most findings of aggregation and adhésion experiments. Discrepancies between calculated and measured values of adhésion forces and rate constants of déposition or detachment could be accounted for in différent ways: 1. Contributions of short-range repulsion, dispersion attraction, and electrostatic i
Data Loading...
