Colloidal particle, deposition

The same molecule has been used as probe to evaluate the SERS efficiency of substrates where ligand molecules are located in a sandwich configuration between two metal surfaces both SERS active [10]. The first one belongs to a silver plate, whose surface roughening was produced via chemical etching with ammonia and hydrogen peroxide the second is a layer of silver colloidal particles deposited after chemisorption of the ligand molecules, as shown in Fig. 20.16. 

Clasen R. Preparation of glass and ceramics by sintering colloidal particles deposited from the gas phase. Glastechn. Ber. 1988 61 119-126... 

Alince, B., Petlicki, J. and van de Ven, T.G.M. (1991) Kinetics of colloidal particle deposition on pulp fibers. I. Deposition of clay on fibers of opposite charge. Colloids cj Surfaces, A, 59, 265-277. 

As can be seen in Figure 11.9, the experimental data are well reflected by the theoretical curves calculated from Equation 11.22 for its between 3 and 4. This observation has a practical implication, proving that colloid particle deposition can be exploited as a sensitive tool for detecting the structure of the surface heterogeneities in the nanometer size range, in particular the charge heterogeneity. 

Thus, the results shown in Figure 11.10 furnish direct support for the heterogeneity hypothesis often used to interpret colloid particle deposition kinetics under a barrier-controlled deposition regime [73]. In these experiments, particle deposition kinetics were determined as a function of salt concentration added to reduce the electrostatic energy barrier. Measured deposition rates were found by orders of... 

Among the many applications of LB films, the creation or arrangement of colloidal particles in these films is a unique one. On one hand, colloidal particles such as 10-nm silver sols stabilized by oleic acid can be spread at the air-water interface and LB deposited to create unique optical and electrooptical properties for devices [185]. 

Splelman L A and Friedlander S K 1974 Role of the electrical double layer In particle deposition by convective diffusion J. Colloid. Interfaoe. Sol. 46 22-31... 

Electrophoretic Plating-the production of a layer of deposit as a result of discharge of colloidal particles in solution onto an electrode. 

Electrophoretic Plating (Electrophoretic Deposition) production of a layer or deposit onto an electrode by discharge of colloidal particles from a solution. 

However, in subsequent studies [23-25,88-90] it was demonstrated that in reality the particle deposition is not a purely geometric effect, and the maximum surface coverage depends on several parameters, such as transport of particles to the surface, external forces, particle-surface and particle-particle interactions such as repulsive electrostatic forces [25], polydispersity of the particles [89], and ionic strength of the colloidal solution [23,88,90]. Using different kinds of particles and substrates, values of the maximum surface coverage varied by as much as a factor of 10 between the different studies. 

The metal formed is deposited on the colloidal particles and causes the absorption of the solution to increase at all wavelengtlK. The depositel cadmium is very reactive. It is reoxidized when air is admitted to the illuminated solution. Addition of methyl viologen to the illuminated solution under the exclusion of air yields the blue colour of the semi-ceduced methyl viologen, MV". As the absorption coefficient of MV" is known, the concentration of reduced cadmium can be readily calculated. reoxidises cadmium atoms ... 

The main disadvantage of the perfect sink model is that it can only be applied for irreversible deposition of particles the reversible adsorption of colloidal particles is outside the scope of this approach. Dahneke [95] has studied the resuspension of particles that are attached to surfaces. The escape of particles is a consequence of their random thermal (Brownian) motion. To this avail he used the one-dimensional Fokker-Planck equation... 

In both experimental and theoretical investigations on particle deposition steady-state conditions were assumed. The solution of the non-stationary transport equation is of more recent vintage [102, 103], The calculations of the transient deposition of particles onto a rotating disk under the perfect sink boundary conditions revealed that the relaxation time was of the order of seconds for colloidal sized particles. However, the transition time becomes large (102 104 s) when an energy barrier is present and an external force acts towards the collector. 

Fig. 21 The fraction of colloidal particles committed to deposit near the transition state. Note that / = at the transition state and that the swing from f = 0 to / = 1 occurs for G/RT 1.

A scaled-up version of this central template-concentric sphere surface assembly approach has been demonstrated for the growth of multi-layer core-shell nano- and microparticles, based upon the repeated layer-by-layer deposition of linear polymers and silica nanoparticles onto a colloidal particle template (Figure 6.8) [60]. In this case, the regioselective chemistry occurs via electrostatic interactions, as opposed to the covalent bond formation of most of the examples in this chapter. The central colloidal seed particle dictates the final particle... 

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