Characterization, film stability

It follows from eqs. (VII.23) and (VII.24) that values of n and A depend on electrolyte concentration. Concequently, the electrolyte concentration defines the height as well as position of potential barrier (see Fig. VII-10), which characterize film stability. The addition of electrolyte to colloidal system results in compression of electrical double layer, and, hence, in compression of the region of the effective action of electrostatic repulsion... 

The foam stability of /3-cas foams progressively decreased with added Tween 20. In contrast, there was a very sharp transition in equilibrium film thickness at R = 0.5. Surprisingly, surface diffusion of /3-cas was not detected at any R value in these films. This was unexpected since it has been reported that adsorbed layers of /3-cas are characterized by a very low surface viscosity [3], signifying that protein-protein interactions in /3-cas films are very weak. We had expected to observe surface diffusion either in the films stabilized by... 

Figure 26.31 depicts the same measuring procedure applied to a contact lens material sheet (A) untreated, (B) (CH4 + air) plasma treated, and (C) (CH4 + air) plasma treated and then O2 plasma treated. Characterizing aqueous film stability on untreated and plasma-modified contact lens materials using artificial tear fluid by... 

Film stability and interfacial forces are important in determining emulsion stability and the likelihood of creaming or complete separation of the phases. Characterization of these interfacial effects is an important factor in determining the fundamental properties that might ultimately determine coalescence kinetics. Some relevant papers and reviews have been published elsewhere (54, 89-96). 

The application of laser light scattering techniques to molecular characterization of dielectric films offers the ability to directly probe chemical bonding within the film and at the film-substrate interface. Real-time measurements can be carried out under ambient conditions or in hostile environments allowing transient film stability studies to be conducted. Such laser-based techniques require only an optically clear line of sight between sample and analyzer and offer several advantages over the high vacuum surface analytical techniques commonly applied to film characterization. These include nondestructive measurement capability, rapid data acquisition time, and ability to use the optical properties of the sample to enhance the sensitivity of the measurement. 

When the gas supply is shut off, G = 0 and Eq. (129) reduces to dzijdt = — pbLj which is the same as Eq. (71). As long as there is no collapse at the top during generation, the motion of the foam/gas interface is determined by the bulk movement of the foam. However, as soon as the thickness of the liquid films at the top decreases to a critical value, the foam begins to collapse and a downward component is superimposed on the bulk movement of the foam. As a result, the net upward velocity of the foam/gas interface decreases. With less stable foams, it is possible to arrive at a steady state when the rate of foam collapse at the top becomes equal to the rate of foam generation (i.e., dzijdt = dz2/dt) and the foam length (z2-zi) does not change with time. This steady state has been used to characterize the stability of shortlived foams. 

Corrosion products formed as thin layers on metal surfaces in either aqueous or gaseous environments, and the nature and stability of passive and protective films on metals and alloys, have also been major areas of XPS application. XPS has been used in two ways, one in which materials corroded or passivated in the natural environment are analyzed, and another in which well-characterized, usually pure metal surfaces are studied after exposure to controlled conditions. 

Sloop and Lerner [132] showed that SEI formation can be affected by treatment of the cross-linked polymer, poly-[oxymeth-ylene oligo(oxyethylene)] (PEM) with an alkylating agent. Cross-linked films of PEM do not form a stable interface with lithium however, upon treatment with methyl iodide, / Ej stabilizes at 2000 Hem"1. Such an SEI is characterized by low conductivity, from 10 to 10 Q-Icm2, which is linear over the temperature range of 25-85 °C. 

Photovoltaic response parameters for electrodeposited (polycrystalline) CdTe thin film electrodes in sulfide-polysulfide or alkaline sodium telluride PEC have been reported, primarily with no reference to the stability of the cells [100], In view of the instability of CdTe in aqueous solutions, Bhattacharya and Rajeshwar [101] employed two methods for the characterization of their electrodeposited CdTe-based PEC. In the first one, a coating of Pb02 (-100 nm thick) was deposited on the CdTe film surface by electroless deposition, and the coated films... 

Simple Fe porphyrins whose catalytic behavior in the ORR has been smdied fairly extensively are shown in Fig. 18.9. Literature reports disagree substantially in quantitative characterization of the catalytic behavior overpotential, stability of the catalysts, pH dependence, etc.). It seems plausible that in different studies the same Fe porphyrin possesses different axial hgation, which depends on the electrolyte and possibly specific residues on the electrode surface the thicknesses and morphologies of catalytic films may also differ among studies. AU of these factors may contribute to the variabUity of quantitative characteristics. The effect of the supporting surface on... 

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