Adhesion electrostatic forces

Electrostatic Adhesion Electrostatic force is generated by conductive materials, which allow electrons to form a difference in electrical charge between the robot and the... 

It is clear that the presence of electrostatic charges, whether due to contact charging, fractoemissions, or some other mechanism, will affect particle adhesion. However, to date there has been no satisfactory attempt made at properly integrating electrostatic forces into partiele adhesion theory. 

In this theory, the adhesion is due to electrostatic forces arising from the transfer of electrons from one material of an adhesive joint to another. Evidence in support of this theory includes the observation that the parts of a broken adhesive joint are sometimes charged [48]. It has been shown that peeling forces are often much greater than can be accounted for by van der Waals forces or chemical bonds. 

For solid surfaces interacting in air, the adhesion forces mainly result from van der Waals interaction and capillary force, but the effects of electrostatic forces due to the formation of an electrical double-layer have to be included for analyzing adhesion in solutions. Besides, adhesion has to be studied as a dynamic process in which the approach and separation of two surfaces are always accompanied by unstable motions, jump in and out, attributing to the instability of sliding system. 

Campbell, S. D. and Hdber, A. C. (1999) Nanometer-scale probing of potential-dependent electrostatic forces, adhesion, and interfacial friction at the electrode/ electrolyte interface. Langmuir, 15, 891-899. 

Dipole-dipole forces are weaker than electrostatic forces, but they can represent a substantial fraction of monopole forces. They have important effects because they are predominantly positive. Therefore, they add up, and even though they decay rapidly with the distance between molecules, their sums remain significant, leading to measurable adhesive forces between macroscopic solid bodies. 

Several types of interaction can be probed with AFM (i) Van der Waals forces and ionic repulsion, (ii) magnetic and electrostatic forces, (iii) adhesion and frictional forces and (iv) the elastic and plastic properties of the surface. In terms of the interactions relevant to electrochemistry, only those interactions typified in (i) will be considered. 

Other explanations of the nature of the polymer to metal bond include mechanical adhesion due to microscopic physical interlocking of the two faces, chemical bonding due to acid/base reactions occuring at the interface, hydrogen bonding at the interface, and electrostatic forces built up between the metal face and the dielectric polymer. It is reasonable to assume that all of these kinds of interactions, to one degree or another, are needed to explain the failure of adhesion in the cathodic delamination process. 

The main forces liable to be exerted on fine particles are calculated in Table I. We can see from this table that the two main parameters that drive the particle adhesion-removal mechanisms are the van der Waals and electrostatic forces. 

Balachandran [23] analyzed the role of electrostatic forces in the adhesion between sohd particles and surfaces. According to the available information this role is not completely clear, the results are contradictory. Electrostatic forces can be significant in the case of polymer and semi-conductor particles. These forces have four main types Coulomb, image charge, space charge and dipole forces. 

The intermolecular forces of adhesion and cohesion can be loosely classified into three categories quantum mechanical forces, pure electrostatic forces, and polarization forces. Quantum mechanical forces give rise both to covalent bonding and to the exchange interactions that balance tile attractive forces when matter is compressed to the point where outer electron orbits interpenetrate. Pure electrostatic interactions include Coulomb forces between charged ions, permanent dipoles, and quadrupoles. Polarization forces arise from the dipole moments induced in atoms and molecules by the electric fields of nearby charges and other permanent and induced dipoles. 

The coarse carrier particles blended with micronized drug form an ordered or interactive mixture (Fig. 8.11) (Hersey 1975) stabilized by adhesive Lifshitz—van der Waals and electrostatic forces (Podczeck 1998 Hickey et al. 1994). The shear forces exerted in the airflow of a DPI device must be greater than the adhesive forces in order to provide sufficient deaggregation and dispersion of the drug particles. Unfortunately, however, this process is more or less incomplete and disperses only a proportion of the agglomerated drug particles depending on the inhalation airflow (Zanen et al. 1992). 

Due to their disperse character and small particle size, silicas are used as flow aids, i.e. they are used to improve the flow behaviour of other materials. The adsorption of the fine silica particles on other type powdered compounds reduces interparticle interactions. Particle adhesion, electrostatic adhesion, Van Der Waals forces and liquid bridge formation is reduced or avoided.33 This allows free-flowing behaviour of strongly interacting or irregularly shaped powdered materials. 

For very fine particles with intimate surface contact, these relatively weak secondary adhesive forces can be quite significant. For example, Rumpf [1] has estimated the contributions of van der Waals and electrostatic forces in agglomerates of fine-grained material. The calculations were made for quartz glass and yielded a binding force due to van der Waals forces between two spheres given by ... 

Adhesion — (a) When two compact materials, be they solid or liquid, are in intimate contact, attractive forces may act between their surface atoms or molecules. These forces are typically - van der Waals forces and electrostatic forces. The work of adhesion W (b)b(a) between the two phases (denoted A and B) is WAB = yA+yB -yAB> where yA and yg are the - interfacial tensions of A and B when each is interfaced only with the vapor phase, and yAB is the interfacial tension of the interface between A and B. In a more rigorous treatment (at thermodynamic equilibrium) each phase is regarded as saturated with the other phase [i]. In the case of liquid phases the equation for the work of adhesion is referred to as the -> Dupre equation. Adhesion forces between particles, or between particles and surfaces, dominate gravity for small particle sizes (pm and sub-pm range). In electrochemistry, increasing attention is being given to various phenomena related to the adhesion of vesicles [ii], particles [iii], droplets [iv], cells [v], etc. to electrode surfaces. 

In addition to these chemical reactions described above, many physical parameters need to be considered as well in terms of post-CMP cleaning. Extensive investigations have been conducted on the correlations between post-CMP cleaning efficiency and relevant physical forces such as the van der Waals force, electrostatic force, particle adhesion, chemical adsorption, surface charge modification, and wettability. It is expected that these factors strongly influence the particle-removal capability of post-CMP cleaning solution. 

First, bacterial adhesion (usually gram-positive cocci and filamentous bacteria) occurs primarily through a Ca + complex formation between carboxyl (COO ) and phosphate (HPOs ) groups of bacterial surface and acquired pelhcle, although van der Waals forces and repulsive electrostatic forces are also present. Some specific bacterial surface proteins also serve as adhesins for specific receptors on acquired peUicle. Pellicle-integrated immunoglobulins also bind bacteria specifically. 

Of critical importance in the development of DPI products is the evaluation, optimization, and control of flow and dispersion (deaggregation) characteristics of the formulation. These typically consist of drug blended with a carrier (e.g., lactose). The properties of these blends are a function of the principal adhesive forces that exist between particles, including van der Waals forces, electrostatic forces, and the surface tension of adsorbed liquid layers [7], These forces are influenced by several fundamental physicochemical properties, including particle density and size distribution, particle morphology (shape, habit, surface texture), and surface composition (including adsorbed moisture) [8]. In addition,... 

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