Hemimicelle

This inequality indicates the amphiphile adopts a shape essentially equivalent to that of a cone with basal area <3. Such cones self-assemble to fonn spheroidal micelles in solution or spheroidal hemimicelles on surfaces (see section C2.3.15). Single-chain surfactants with bulky headgroups, such as SDS, typify surfactants in this category. 

Figure C2.3.15. Hemimicelle stmctures (a) monolayer type hemimicelle (b) spheroidal, globular hemimicelle.

Figure C2.3.17. Model of half-cylindrical aggregates (hemimicelles) on a crystalline hydrophobic substrate, such as for tetradecyltrimethylammonium bromide on M0S2 [91], Adapted from figure 2 of [89],...

Manne S, Cleveland J P, Gaub FI E, Stucky G D and Flansma P K 1994 Direct visualization of surfactant hemimicelles by force microscopy of the electrical double layer Langmuir 10 4409-13... 

Gu Y and Fluang Z 1989 Thermodynamics of hemimicellization of cetyltrimethylammonium bromide at the silica gel/water interface Colloids Surf. 40 71-6... 

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. 

Fig. 29. STM image of a Au(l 11) electrode in 0.5 M H2SO4 + 0.4 mM CuS04 + 0.1 sodium dodecyl sulfate (SDS) at +0.27 vs. Cu/Cu++. SDS adsorbs at this potential on Au(lll) as hemimicelles, forming a line pattern on the surface [97, 98],...

Hemicyanine dyes, 9 257 Hemihedrite, 6 471t Hemiisotactic micro structures, 16 108 4,6-Hemiketals, 24 595 Hemimicelle formation, 24 142 Hemins, 14 552... 

The adsorption isotherm obtained for dodecylsulfonate (CDS) on alumina is given in Figure 2. This isotherm is similar to that obtained in the past for sulfonate/alumina systems (4). This isotherm behaves in an s-shaped manner (6) revealing its four characteristic regions of adsorption 1) Electrostatic interaction 2) Lateral association (hemimicellization), 3) Electrostatic hindrance and 4) micellization. 

Keywords Fluorescence probing Hemimicelle Micellar fluidity Micelle Organized assemblies in solution and interfaces Polarity parameter Pyrene... 

Some surfactants aggregate at the solid-liquid interface to form micelle-like structures, which are popularly known as hemimicelles or in general solloids (surface colloids) [23-26]. There is evidence in favor of the formation of these two-dimensional surfactant aggregates of ionic surfactants at the alumina-water surface and that of nonionic surfactants at the silica-water interface [23-26]. 

These fluorescent probes have been successful in reporting the structural parameters of surfactant assemblies such as micelles [103], reverse micelles [104], ternary systems [105], swollen micelles [106], microemulsion [107], vesicles [108], liposomes [109], hemimicelles [110], monolayers [111] and bilayers [111]. 

Fig. 36 Schematic diagram of surfactant-adsorption on silica surface as monomer, hemimicelle, and at surfactant concentration above CMC where pyrene is bound to micelle...

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). 

To conclude, we should also point out that condensed phases containing the organic compound of interest can be formed at the particle surfaces. Such phenomena occur in cases involving ionic organic compounds that form micelles/hemimicelles... 

Note these data also indicated a preference for DS over the competing chloride concentration of between 30 and 60. This implies the dodecylsulfonate was accumulated in the diffuse double layer surrounding the alumina relative to its bulk solution concentration more than an order of magnitude more preferentially than the inorganic chloride adsorbate. As a consequence, it is perhaps not surprising that Fuerstenau and Wakamatsu (1975) observed the accumulation of hemimicelles on the alumina at only about 400 /jM (pH 7.2) and about 7 fjM (pH 5.2) bulk DS-concentrations (see discussion of hemimicelles). 

Chandar, S., D. W. Fuerstenau, and D. Stigler, On hemimicelle formation at oxide/water interfaces . In Adsorption from Solution, R. H. Ottewill, Ed., Academic Press, London, 1983, pp. 197-210. 

Fuerstenau, D. W., Streaming potential studies on quartz in solutions of ammonium acetates in relation to the formation of hemimicelles at the quartz-solution interface , J. Phys. Chem., 60, 981-985 (1956). 

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