Stabilizers adsorption

Figure 9 The schematical representation of dispersion polymerization process, (a) initially homogeneous dispersion medium (b) particle formation and stabilizer adsorption onto the nucleated macroradicals (c) capturing of radicals generated in the continuous medium by the forming particles and monomer diffusion to the forming particles (d) polymerization within the monomer swollen latex particles, (e) latex particle stabilized by steric stabilizer and graft copolymer molecules (f) list of symbols.

A representative TEM image of the sonochemically formed Au particles in the absence of stabilizer is shown in Fig. 5.9 [33]. In this experiment, only 20 mM of 1-propanol is included as an organic additive. It can be seen that the size of Au particles is in the nanometer regime. The sizes of the sonochemically formed metal nanoparticles are dependent on the initial concentration of metal ions and the types of stabilizers [26] as same as the conventional methods smaller metal particles are formed in the presence of lower initial concentration of metal ions. In addition, if a suitable stabilizer were used, the growth of particles would be suppressed effectively by the stabilizer adsorption on the particle surface, resulting in the formation of smaller metal particles. 

Various anionic compounds such as halides, carboxylates or polyoxoanions, generally dissolved in aqueous solution, can establish electrostatic stabilization. Adsorption of these compounds onto the metallic surface and the associated countercations necessary for charge balance produces an electrical double-layer around the particles (Scheme 9.1). The result is a coulombic repulsion between the particles. At short interparticle distances, if the electric potential associated with the double layer is sufficiently high, repulsive forces opposed to the van der Waals forces will be significant to prevent particle aggregation. 

The properties of zeolites, most notably their stability, adsorptive capacity and catalytic activity, are strongly dependent on the precise location of Si and A1 in the emionic framework. This is one of the most challenging and debated problems in silicate crystal chemistry. 

After all other conditions had been optimized, the effect of temperature during the adsorption step was studied again, particularly because the temperature reduction from 150° to 100 °C had no deleterious effect on dispersion stability. Adsorption of the block copolymer onto the titanium dioxide at room temperature would be easy to carry out in practical applications and might be worth even a sacrifice in dispersion stability. Figure 4 shows settling data of dispersions prepared in a Waring... 

In the case of alkane cracking, dispersion forces between the alkane molecules and the siliceous walls of the zeolites and perhaps other nanoporous crystalline and ordered materials are possibly the most important interactions for stabilizing adsorption in the cavities, since the proton affinity of alkanes is low [104] and the electrostatic interactions between the alkane and the adsorbent are negligible [97],... 

Long chain polymers, such as proteins, can often adsorb to the surface of colloidal particles (because they gain adsorption energy), which can have a significant influence on coUoidal stability. Adsorption of polymeric material at an interface takes place in such a way that the chains can extend from the... 

Thus, the stability of aqueous dispersions of CuPc depends on the efficiency of the stabilizer adsorption on its surface. Treatment in an ultrasonic field allows to increase the efficiency of the stabilizer adsorption and therefore to increase the stability of pigment dispersions. 

On the basis of the results obtained, it can be assumed that during the ultrasonic treatment of CuPc aqueous dispersions the deagglomeration of pigment panicles that is accompanied by the formation of "fresh" surface with increased energy takes place, which leads to an activation of the stabilizer adsorption and the increased stability of dispersions. 

Carbonic 28 days with heparin stabilizer Adsorption, aggregation, and denaturation (24,25)... 

The behavior of disperse systems, such as foams and emulsions, is very complex and there have been only few attempts to derive qualitative and quantitative relationships between their stability and physicochem-ical parameters of the stabilizing adsorption layers. The starting point of most of these approaches is the hydrodynamic theory of thinning of a liquid film between two bubbles or drops according to Reynolds (1) and Levich (2). A simplified picture of the general scenario in an emulsion is the following. When two... 

Some approaches analyzed directly flic influence of flic stabilizing adsorption layers and concluded that diere is a dependence of the stability of an emulsion on flic interfacial concentration and the sum of inter-molecular interactions (8—10). Murdoch and Leng (11) pointed out the role of bulk and interfacial rheological parameters to describe these processes. This concept was further treated by several authors (12—14). A very comprehensive approach was given by Wasan and co-workers (15,16) who considered the surface shear and dilational rheology, and also some hy-drody-namic parameters in their analysis of emulsion films. 

Further information is obtained if the amount of liquid adsorbed on the surface of the particle is also determined, permitting the combination of the data on heat of immersion with those on the amount of adsorbed liquid. Thus, molar adsorption enthalpies can be given for the characterization of the stabilizing adsorption layer [12-16]. A further benefit of adsorption excess isotherms is that it is possible to calculate from them the free enthalpy of adsorption as a function of composition. When these data are combined with the results of calorimetric measurements, the entropy change associated with adsorption can also be calculated on the basis of the second law of thermodynamics. Thus, the combination of these two techniques makes possible the calculation of the thermodynamic potential functions describing adsorption [14,17-19]. 

In calculations of stability for disperse systems, knowledge of the thickness of the stabilizing adsorption layer is highly important [36,39]. If the specific sur-... 

The diversity of carbon as an electrode material stands from its bulk and surface properties, particularly the structural polymorphism, chemical stability, rich surface chemistry and electronic conductivity. Although some carbons present electronic properties close to those of metallic electrodes, their properties are very different among the various members of the carbon family, as depend on the spatial arrangement of the carbon atoms. Since the choice of an electrode material is dictated by electron transfer rate, stability, adsorption or redox potential, it is important to bear in mind the main structural and physicochemical differences of most widely used carbons in electrochemical applications. 

Adsorption of ionic, nonionic and polymeric surfactant on the agrochemical solid gives valuable information on the magnitude and strength of the interaction between the molecules and the substrate as well as the orientation of the molecules. The latter is important in determining colloid stability. Adsorption isotherms are fairly simple to determine, but require careful experimental techniques. A representative sample of the solid with known surface area A per unit mass must be available. The surface area is usually determined using gas adsorption. N2 is usually used as the adsorbate, but for materials with relativdy low surface area, such as those encountered with most agrochemical solids, it is preferable to use Kr as the adsorbate. The surface area is obtained from the amount of gas adsorbed at various relative pressures by application of the BET equation [96]. However, the surface area determined by gas adsorption may not represent the true surface area of the solid in suspension (the so-called wet surface). In this case it is preferable to use dye adsorption to measure the surface area [99]. 

In considering how SERS intensities can be affected by electrode potential in the absence of a redox process, it is to be expected that for many molecules the surface concentration, F, can change with potential, i.e., F = F(V). It should be mentioned that SERS-active surfaces stabilize adsorption so F(V) may be less affected by potential on a rough surface than on a smooth surface. Figure 25 shows that the position of the I versus V profile depends on the vibrational mode. Obviously, if different bands show very different / versus V curves, there are other factors in addition to the surface concentration which depend on potential and which affect intensities. Changes in orientation of surface molecules as a function of electrode potential have been considered... 

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