Surface colloidal particles

To prove the above statement on the determining effect of electric charge of both the CdS colloidal particle surface and the quencher molecule on the adsorption of these molecules from aqueous solution, we have modified the surface of colloidal CdS during its preparation. The most efficient method of such modification consists in changing the surface charge of the colloidal particle via the preparation of nonstoichiometric colloid. In this case, the surface charge is determined by the charge of excessive ion (either S 2 or Cd2+). 

The ability of a luminescence quencher molecule to adsorb on the surface of ultradispersed colloidal semiconductor in aqueous solutions was shown to depend mainly on the charge of the colloidal particle surface and the charge of quencher ions. 

A slow dark relaxation can be naturally explained within the suggested model by the unblocking the sulfur atoms shaded from interaction with S032- during the some dark process, followed by sulfur removal from the colloidal particle surface in the form of thiosulfate anion and adsorption of a new hydrosulfide anion. 

Note, that the variation in the concentration of the MO at the initial part of the kinetic from [MO] = 10 4M to [MO] = 0.8-10 4M - A[MO] = 0.2-10 4M corresponds to the MO amount initially adsorbed at the colloidal particle surface [K]-MOad = 2-10 7 M 100 = 2-10 5 M. In this case, one may see from the experimental data obtained (see, e.g., Fig. 2.23) that at the initial step of the reaction, the reaction quantum yield decreases only two-fold. Therefore, the desorption rate of the low-molecular components can not be much lower than the rate of the reaction proceeding on the CdS particle. Since the reaction quantum yield does not change with the varying the light intensity, the desorption of the low-molecular components is a much faster than the redox transformations at the photocatalyst surface. 

Thus, the adsorption layer at the colloidal particle surface is represented by the segments (areas) of at least two types, which differ significantly in the time of establishing the adsorption-desorption equilibrium with respect to the characteristic time of photocatalytic overall reaction. A part of the surface of particle is not coated with the PAA molecules, and for this part... 

Within the model of a semiconductor particle with two surfaces of different ( active and passive ) adsorption layer types, one may quantitatively describe the initial part of kinetic curves. Denote the total surface area of the colloidal particle as 2, and the surface area of the colloidal particle blocked by PAA as 2PAA. Let us call the colloidal particle surface area free of PAA as the working surface and denote it as 2W = 2 - 2PAA. 

The similar patterns of incipient instability observed for both nonaqueous and aqueous dispersions implicate the London attraction between the core particles in the coagulation of incompletely covered dispersions. It seems likely that under the stress generated by a Brownian collision, the well-anchored stabilizing chains can move laterally on the surface of the colloidal particles ( surface migration ). This creates bare patches on the surface of the... 

By contrast, the role of colloids in C-C coupling reactions, especially the Heck and Suzuki reaction, is currently the topic of debate [54—57]. Possible mechanistic pathways include the colloidal particles being in equilibrium with mononuclear complexes, which are the active species (Figure 3a), or reaction occurring directly on colloid particle surface atoms (Figure 3b). For hydrosilylation, the importance of platinum colloids has long been recognized [58]. 

One of the three major ways in which a particle can acquire a surface charge is by chemical reaction at the particle surface. This phenomenon, which frequently involves hydrogen ions and is pH-dependent, is typical of hydroxides and oxides. As an illustration of pH-dependent charge on colloidal particle surfaces, consider the effects of pH on the surface charge of hydrated manganese oxide, MnOjCHjO) (s). In a relatively acidic medium, the reaction... 

Ion absorption is a second way in which colloidal particles become charged. This phenomenon involves attachment of ions onto the colloidal particle surface by... 

Figure 6-13. Transmission electron micrograph of 36 nm gold colloid particles stabilized with P(m-C6H4S03Na)3. The mean distance between colloid particle surfaces corresponds to two layers of the ligand. (Reproduced by permission from ref. [175].)...

Many reviews, books, proceedings, and chapters have been published on the topic. Serious LLS users should consult References (1) and (2) and other books, rather than proceedings or articles, as reference materials. In particular, the first monograph on the theoretical aspects of dynamic LLS (6) is highly recommended because it remains as the best source reference. In this article there is concentration on experimental detail. Often, static and dynamic LLS are used separately generally, polymer chemists are more familiar with static LLS and only use dynamic LLS to size particles, whereas polymer physicists are not custom to precise static LLS measurements and sample preparation. This seriously limits their application. This article specially deals with this problem by using several typical examples to show how static and dynamic LLS can be combined to extract more information, such as the characterization of molar mass distribution, estimation of composition distribution of a copolymer, the adsorption/grafting of polymer chains on colloidal particle surfaces, and the self-assembled nanostructure of block copolymers. 

The Debye length, at room temperature may be estimated as /Id = 0.308/v nm, where C is the molar concentration of salt (1 M = 10 mol m ). Note that when the volume fraction of colloidal particles (p is not low, the Debye length Id becomes dependent on p, colloidal particle radius, r, and colloidal particle surface charge density, a [11] ... 

The pioneering Gouy-Chapman theory can be used to quantitatively describe the diffuse electrical double layer. The electrical potential at a distance X from the colloidal particle surface (i f(x)) is described by the onedimensional Poisson s equation that relates the number of charges per unit volume (or space charge density, p) to /(x). 

Figure 6.10 Strength of the van der Waals forces between colloid particles/surfaces. Even for particles as small as 20 nm in radius their potential energy exceeds I

If another species of colloidal particles is added to the original suspension, an attractive interaction due to osmotic pressure, termed a depletion force, arises. The size of the second particle species should be intermediate between that of the colloidal particles and of the solvent molecules. Typically, a polymer that does not adsorb to the colloidal particles surface is used. 

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