Reverse micelles RMs

The partitioning behavior of biomolecules in RME can be regulated by varying the size and shape of the reverse micelles (RMs). This can be easily ac-... 

The basic processes of dissolution, acid-base interaction, micellization, solubilization, oxidation and reduction take place in oil formulation. During engine operation, additives of the lubricant interact continuously with engine surfaces and themselves. Thus, there is a progressive change in the surface due to the lubrication, friction, and wearing processes, tribofilm formation, and oxidation. All these processes are presented and discussed throughout this book. Surfactant additives are fundamental to reverse micelles (RMs) formation in oil... 

Fig. 1.2. Dependence of free-energy changes (AG° mic) of micellization of surfactants in high, intermediate, and low-polar solvents. Normal micelle (M) to reverse micelle (RM) transition as function of polarity (e) of the medium. Surfactants in a medium of optimum dielectric constants 38 to 41 do not aggregate but remain in the monomeric state (n)...

The additive mixtures interact in a variety of ways, both in the bulk oil and on surfaces. Tribochemical interactions of additives in the oil formulation are discussed in Chapter 2. Surfactant molecules, when dissolved in base oil, are capable of self-organization to form aggregates such as soft-core reverse micelles (RMs). The polar or charged head groups of these molecules with the counter ions form the interior of the micelle (core), and the hydrocarbon chains made up its external shell. The most important factor governing the tribochemical reactions under boundary lubrication is connected with the action of soft-core and hard-core reverse micelles discussed in Chapter 3. 

Examples of such surfactants are detergents which include calcium and magnesium sulfonates (RSOO)2M2+, phenates (RC6H40)2M2+, carboxylates (RCOO )2M2+, phosphonates RPO/M2 and carbonate-sulfonate hard-core reverse micelles (RMs). Ashless dispersants are the most widely used types, such as the substituted polyisobutylene amine succinimides (mono-substituted, m-PIBS and bis-substituted, b-PIBS), succinate esters, Mannich bases, and phosphorus types, see Chapter 2.2 for formulas (Inoue and Watanabe, 1983 Papke and Rubin, 1992 Vipper and Watanabe, 1981). 

Table 2.2. Typical parameter values for calcium sulfonates, alkylphenyl sulfides and alkylsalicylates detergents with additional total base number (TBN, mgKOH/g oil) from calcium carbonate. Formation of hard-core reverse micelles (RMs) of calcium carbonate-sulfonate or alkylphenate and soft-core revere micelles (RMs) of calcium alkylsalicylate in oil formulations...

Solubilization of insoluble oxidation products and soot particles. Reverse micelles (RMs) formations manage the prevention of agglomeration and the contamination process of insoluble oxidation particles and soot particles by both steric stabilization (Fig.2.1) and electrostatic stabilization mechanisms (Fig.2.2). The steric stabilization mechanism provides a physical barrier to agglomeration of particles by adsorption on particle surfaces. Adsorbed dispersant acts as a physical barrier to attraction between particles. 

Fig. 2.11. Solubilization mechanism of zinc dialkyldithiophosphate molecules (ZDDP) by soft-core reverse micelles (RMs)...

Fig. 3.1. Schematic representation of normal micelle (M) in water, a soft-core reverse micelle (RM) and hard-core reverse micelles (RM) in hydrocarbon formulation, ( AAAO ) detergent molecule...

Table 3.11. The chemistry of tribofilm generated by multifunctional additives composed of soft-core and hard-core reverse micelles (RMs) in oil formulation. Evaluation of tribofilm by XANES spectroscopy (Varlot et al., 2001)...

Soft-core and hard-core reverse micelles, RMs The retardation of the decomposition of ZDDP by soft-core and hard-core RMs appears promising for high performance engine oils as shown in Table 3.11. Compare the chemistry of tribochemical films generated by multifunctional soft-core and hard-core RMs systems. 

One of the main problems in modern nanotechnology is the preparation and stabilization of nanoparticles of different nature semiconductors, metals, organic compounds, etc. Nowadays there are a number of methods for nanoparticle synthesis [1]. Among them water-in-oil reverse micelles (RMs) are the successful technique for the controlled preparation of very small and monosized nanoparticles. Water-in-oil RMs are thermodynamically stable dispersion of nanosized water drops in organic solvent, stabilized by surfactants. RMs are formed spontaneously due to the surfactants, which diminish the interface tension down to ultralow values, and as a result the free energy decreases when the total oil-water interfacial area increases. Thermodynamically stable water-in-oil microemulsions can be produced at strictly defined conditions. It is possible to change the size of the water pool of RMs by variation of the ratio between water and surfactant concentrations. This allows changing the size of nanoparticles, which are stabilized in such microemulsions. 

Microheterogeneous environments, such as those found in reverse micelles (RMs) and microemulsions, have tremendous promise because of the nonstandard environments they present. Often, chemistries that occur in these solutions do not occur in homogeneous liquid solutions [1-4]. Essentially, RMs are spatially ordered macromolecular assemblies of surfactants formed in nonpolar solvents, in which the polar head groups of the surfactants point inward toward a polar core and the hydrocarbon chains point outward toward the nonpolar medium [5, 6] (see schematic representation in Fig. 14.1). 

Microemulsions are thermodynamically stable, isotropic transparent mixtnres of two immiscible liqnids (polar and nonpolar) and an amphiphilic component (nsuaUy surfactants and cosnrfactants). The microheterogeneous environments present in reverse micelles (RMs) and microemnlsions hold potential promise for apphcations in different fields owing to the nonstandard environments they produce. Often, these systems exhibit entirely different chemistry than that observed in homogeneous liquid solutions [17,18]. Microemnlsions are capable of solubilizing both polar and nonpolar substances and have wide apphcations [19, 20] in various fields such as chemical reactions [21], preparation of nanomaterials [22], and drug delivery [23]. 

Poly(ethyleneimine) Poly(ethyleneimine) is a branched polyamine (M = 1800) consisting of a 1 2 1 ratio of primary, secondary and tertiary amines that makes it structurally similar to polyamines isolated from S. tumis and C. Judformis [85]. These PEls were integrated as spherical reverse micelles (RMs) made from bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) in iso-octane, providing a constrained environment for silica precipitation. These RMs exchanged their contents... 

The distinction between reversed micelles (RMs) and reversed miCToemul-sions is often ill-defined. Water molecules added to an RM are not distributed evenly throughout the hydrocarbon continuum but are found associated with the surfactant head groups. This is also described as swollen reversed micelle. The volume of water that can be taken up and be stabilized in the swollen reversed micelle is limited. The swollen reversed micelles are also often called reversed microemulsion. In RMs, the amount of solubilized water is less than or equal to the amount necessary to hydrate the surfactant head groups. Solubilization of water over and above this threshold results in the formation of an isotropic and thermodynanucally stable water-in-oil microemulsion. ... 

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