Aggregate surface

The fonnation of surface aggregates of surfactants and adsorbed micelles is a challenging area of experimental research. A relatively recent summary has been edited by Shanna [51]. The details of how surfactants pack when aggregated on surfaces, with respect to the atomic level and with respect to mesoscale stmcture (geometry, shape etc.), are less well understood than for micelles free in solution. Various models have been considered for surface surfactant aggregates, but most of these models have been adopted without finn experimental support. 

Leimbach J, Sigg J and Rupprecht FI 1995 The existence of small surface aggregates-surface micelles on polar charged surfaces Colloids Surf. A 94 1-11... 

Figure 4.20 shows variation of electric conductivity of ZnO film in time during bombardment with silver atoms and under conditions, when the atomic beam was terminated. We believe, that the obtained results (the behaviour of conductivity in time, its relaxation) can be explained by competition of adsorption and surface aggregation of adatoms leading to the appearance of larger particles of silver (dimers, trimers, and so on) on the surface. Such particles were assumed not to provide a consid-... 

Figure 4.21 illustrates the validity of an integral form of the rate equation governing aggregation of silver atoms at several temperatures. The activation energy of surface aggregation (second order) was found... 

Therefore, the use of a combination of sensors (sensor-substrate and sensor-detector of emitted atoms) enabled us to obtain unique information concerning the mechanism of emission of adsorbed atoms of silver in the course of their surface aggregation. The data obtained makes it possible to provide an insight of mechanisms and energetics of condensation-stimulated phenomena [11]. 

Two examples from literature illustrate this approach nicely. Moore et al.114 assembled thiol-terminated long-chain S204-crown TTF onto Au and Pt surfaces by thiolato-metal bonds (see Figure 12). In the presence of various cations, most successfully Ag+, small differences were observed in the first oxidation potential (typically 60-80 mV). Similar responses were observed in solution state experiments with the same materials. The SAMs were stable when electrochemically cycled over the first oxidation wave but unstable when scanned beyond this point. Liu et al.115,116 prepared SAMs of 45 and 46 on Au substrate. Anchored to the solid surface by four Au S bonds per molecule, these SAMs were stable for hundreds of cycles over the full oxidation range. In response to the presence of Na+ both the TTF oxidation waves were shifted anodically by 55-60 mV. This observation was ascribed to either surface aggregation or cooperativity of neighbouring crown rings. 

Surface aggregation structure of the monolayer based on gold decoration technique... 

Both of these methods are commonly used in the literature for analysis of irregular surface aggregates and porous materials, and both physisorption and chemisorption have been applied... 

Equations 27 and 28 present the extension of the Szyszkowski-Langmuir model to the adsorption of one-surfactant systems with aggregation at the interface. For the formation of dimmers on the surface, n = 2 and Eqs. 27 and 28 can be expanded to obtain the Frumkin equation of adsorption state. In general, the surface aggregation model described by Eqs. 27 and 28 contains four free parameters, including coi, n, b and Fc, which can be obtained by regression analysis of the data for surface tension versus surfactant concentration in the solution. 

Fig. 39 Schematic diagram showing the formation of A interparticle surface aggregates which causes flocculation B aggregates with monomers in solution leading to dispersion...

The thermodynamics of mixing upon formation of the bilayered surface aggregates (admicelles) was studied as well as that associated with mixed micelle formation for the system. Ideal solution theory was obeyed upon formation of mixed micelles, but positive deviation from ideal solution theory was found at all mixture... 

Surface aggregates formed by ionic surfactant adsorption on oppositely charge surfaces have been shown to be bi layered structures (1.) and are called admicelles<2) in this paper, though they are sometimes referred to as hemimicelles. The concentration at which admicelles first form on the most energetic surface patch is called the Critical Admicellar Concentration (CAC) in analogy to the Critical Micelle Concentration (CMC), where micelles are first formed. Again, in much of the literature, the CAC is referred to as the Hemimicellar Concentration (HMC). 

When milk at a pH of less than 6.5 is heated for 20 to 30 min at 100°C, it coagulates to form a gel. Casein micelles isolated from such milk have denatured whey protein attached to micelle surfaces (Creamer et al. 1978). Such micelle surfaces aggregates of whey pro-... 

The result was interpreted under two scenarios in which 1) discrete molecules or 2) surface aggregates of the block copolymers should exist at the air - water interface at different compression states. 

AFM) as a function of different compression state, they have used a modified approach to interpreted the it - A isotherms of these amphiphilic block copolymers in which they took into account the presence of the surface aggregates at the air -water interface. 

Degradation pathways for proteins can be separated into two distinct classes chemical and physical. Chemical instability is any process which involves modification of the protein by bond formation or cleavage. Physical instability refers to changes in the protein structure through denatur-ation, adsorption to surfaces, aggregation, and precipitation [15]. 

Shape of interior surface Aggregation and 0 0 poor very much much... 

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