Adsorption mechanisms particle surfaces

As a contaminant moves through soil and groundwater, chemical processes will affect both contaminant concentration and overall hydrogeochemistry (Schoonen, 1998) of the system. Different adsorption mechanisms cause pollutants to adsorb onto the soil, volatilize, precipitate, and be part of the oxidation-reduction processes. Adsorption is loosely described as a process in which chemicals partition from a solution phase into or onto the surfaces of solid-phase materials. Adsorption at particle surfaces tends to retard contaminant movement in soil and groundwater. 

Solubilization of insoluble oxidation products and soot particles. Reverse micelles (RMs) formations manage the prevention of agglomeration and the contamination process of insoluble oxidation particles and soot particles by both steric stabilization (Fig.2.1) and electrostatic stabilization mechanisms (Fig.2.2). The steric stabilization mechanism provides a physical barrier to agglomeration of particles by adsorption on particle surfaces. Adsorbed dispersant acts as a physical barrier to attraction between particles. 

Kendall, M., Brown, L and Trought, K. (2004) Molecular adsorption at particle surfaces a PM toxicity mediation mechanism. Inhalation Toxicology, 16 (Suppl.), 99 105. 

The presence of moisture on steel above the critical humidity but below the saturation point may be caused by an adsorption mechanism or by the presence of particles of deliquescent salts on the surface. Once rusting has begun, the composition of the rust already formed will influence the relative humidity at which further rusting will occur, because rusts formed in polluted atmospheres contain hygroscopic salts. The method by which moisture reaches the surface is probably less important, however, than the length... 

Suspension Model of Interaction of Asphaltene and Oil This model is based upon the concept that asphaltenes exist as particles suspended in oil. Their suspension is assisted by resins (heavy and mostly aromatic molecules) adsorbed to the surface of asphaltenes and keeping them afloat because of the repulsive forces between resin molecules in the solution and the adsorbed resins on the asphaltene surface (see Figure 4). Stability of such a suspension is considered to be a function of the concentration of resins in solution, the fraction of asphaltene surface sites occupied by resin molecules, and the equilibrium conditions between the resins in solution and on the asphaltene surface. Utilization of this model requires the following (12) 1. Resin chemical potential calculation based on the statistical mechanical theory of polymer solutions. 2. Studies regarding resin adsorption on asphaltene particle surface and... 

As an example of composite core/shell submicron particles, we made colloidal spheres with a polystyrene core and a silica shell. The polar vapors preferentially affect the silica shell of the composite nanospheres by sorbing into the mesoscale pores of the shell surface. This vapor sorption follows two mechanisms physical adsorption and capillary condensation of condensable vapors17. Similar vapor adsorption mechanisms have been observed in porous silicon20 and colloidal crystal films fabricated from silica submicron particles32, however, with lack of selectivity in vapor response. The nonpolar vapors preferentially affect the properties of the polystyrene core. Sorption of vapors of good solvents for a glassy polymer leads to the increase in polymer free volume and polymer plasticization32. 

The measurements of the reaction activation energies indicated that the reaction mechanism in the nanomatrix was different than in the bulk solution. Both adsorption-based diffusion and simple diffusion appeared to control the reaction rate in the nanomatrix. The adsorption-based diffusion corresponded to the relatively fast reaction of the doped TTMAPP, which were close to the particle surfaces. The simple diffusion correlated to the slow reaction of the deeply embedded TTMAPP. 

As we consider the mechanical properties of SPs, it is often useful to consider them in the context of entanglements, which are intermolecular interactions that transfer mechanical forces from one molecule to the next. In this chapter we use the term entanglement in a very general way, so that it includes topological entanglements (one polymer chain is physically wrapped around another), chemical entanglements (attractive intermolecular interactions between polymer chains), and surface adsorption (attractive intermolecular interactions between polymer chains and a particle surface, e.g., from a filler). The important, fundamental characteristic is that it is an interaction that allows a mechanical stress on one molecule to be distributed or transferred to another molecule with which it is entangled. 

If particles enter the surface activated complexes directly from the volume, e.g., when the reaction occurs as a result of impact of molecules from the gas phase upon the adsorbed molecules, the expression for the reaction rate will contain, together with surface concentrations, the values of volume concentrations. These impact mechanisms were long ago proposed by Langmuir (22) for the reactions of CO and H2 with 02 on the surface of platinum the reaction occurs at the impact of a CO or H2 molecule against an adsorbed O atom. Such reactions seem to be numerous (23). Along with this, the above-mentioned adsorption mechanisms that involve the reaction between two adsorbed particles are possible. Elementary acts of surface reactions in which more than two particles participate are hardly probable. 

Correlation of logKp vs. log p([ have been explained as a combination of both adsorption to the surface of the particle and absorption into an organic surface layer [59]. More recently partitioning to the surface of soot carbon has been suggested as playing an important role in this gas/particle distribution [60]. While the relative importance of these mechanisms remains unclear, the overall behavior can be summarized by the following equation [59] ... 

The mechanism of particle capture by depth filtration is more complex than for screen filtration. Simple capture of particles by sieving at pore constructions in the interior of the membrane occurs, but adsorption of particles on the interior surface of the membrane is usually at least as important. Figure 2.34 shows four mechanisms that contribute to particle capture in depth membrane filters. The most obvious mechanism, simple sieving and capture of particles at constrictions in the membrane, is often a minor contributor to the total separation. The three other mechanisms, which capture particles by adsorption, are inertial capture, Brownian diffusion and electrostatic adsorption [53,54], In all cases, particles smaller than the diameter of the pore are captured by adsorption onto the internal surface of the membrane. 

Consider a reactive species A in a solution in contact with soil particles. Its concentration at the interface where the reaction is taking place is CA. The rate of the reaction at the surfaace will therefore depend on the concentration at the interface, which is itself directly dependent on the rate of the actual adsorption mechanism at the surface or at interlayer sites. Assuming a first-order reaction, the rate is defined as... 

We also note that carboxylate ions which are chemically combined at the polymer-water Interface are known to be considerably more effective in conferring mechanical stability upon a latex than are carboxylate ions which are held at the interface by adsorption. Presumably this is because the latter are able to move laterally in the particle surface, whereas the former are not.) We propose that a given number of adsorbed soap anions is more effective in conferring mechanical stability if able to move independently of... 

Modified Gouy-Chapman theory has been applied to soil particles for many years (Sposito, 1984, Chapter 5). It postulates only one adsorption mechanism -the diffuse-ion swarm - and effectively prescribes surface species activity coefficients through the surface charge-inner potential relationship contained implicitly in the Poisson-Boltzmann equation (Carnie and Torrie, 1984). Closed-form... 

If the sole mechanism of ion adsorption is via the diffuse-ion swarm, the anions in an electrolyte solution in which clay mineral particles are suspended will, in general, be excluded from a portion of the suspension volume near the particle surface [23,27]. If q- is the specific adsorbed charge of anions resulting from this exclusion and c is their bulk concentration in a 1 1 electrolyte... 

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