Amphiphilic surfactants

In emulsion polymerization, a solution of monomer in one solvent forms droplets, suspended in a second, immiscible solvent. We often employ surfactants to stabilize the droplets through the formation of micelles containing pure monomer or a monomer in solution. Micelles assemble when amphiphilic surfactant molecules (containing both a hydrophobic and hydrophilic end) organize at a phase boundary so that their hydrophilic portion interacts with the hydrophilic component of the emulsion, while their hydrophobic part interacts with the hydrophobic portion of the emulsion. Figure 2.14 illustrates a micellized emulsion structure. To start the polymerization reaction, a phase-specific initiator or catalyst diffuses into the core of the droplets, starting the polymerization. 

Figure 2.14 Schematic Illustration of micelles stabilized by amphiphilic surfactant... 

The structure of water droplets (often termed water pools) entrapped in spherical or near-spherical associations of amphiphilic surfactants is quite different from that of bulk water their polarity, microviscosity, and behavior as a function of temperature reflect the uniqueness of such media. 

Lysophosphatidilo lipids These are amphiphilic surfactants produced in a natural way from phospholipids by phospholipases. Their mechanism of action as a promoter is not fully understood. It is supposed that, like other surfactants, they can affect intracellular proteins and polar groups of phospholipids in intercellular spaces, which may favor the formation of channels permitting the penetration of water and substances dissolved therein [45]. 

There is a vast body of diblock copolymer studies since block choice can be such that they resemble amphiphilic surfactants. For the sake of brevity, we will skip them. Instead, we present an interesting case of triblock copolymers of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, commonly known by one of its trade names, Pluronics [117]. They have been used as non-ionic surfactants for a variety of applications such as in emulsification and dispersion stabilization. In aqueous solutions, these copolymers form micelles, and there exists a well-defined critical micelle concentration that is experimentally accessible. Several groups have investigated colloidal suspensions of these polymers [118-122], The surface properties of the adsorbed monolayers of the copolymers have been reported with respect to their structures and static properties [123-126]. 

Micelles are formed in order to protect the hydrophobic regions of the amphiphilic surfactant from the aqueous solution. The surface area S occupied by the surfactant molecule can be determined by ... 

An interesting phenomenon in water-oil-amphiphile systems is the presence of self-assembled arrays of amphiphiles (surfactants) called micelles. From 1948 to 1950, Philip Alan Winsor reported that upon simple mixing (i.e., without the need for high shear conditions), oil, water, and amphiphiles yielded clear, macro-scopically homogeneous single phases which he termed type IV systems (Winsor, 1948, 1950). The term microemulsion was introduced later by Jack H. Shulman, a Columbia University chemistry professor, to denote these thermodynamically stable optically isotropic, transparent oil-water-amphiphile dispersions (Shulman et al., 1959). Type IV systems contain small droplets of one liquid dispersed within the other, with a self-assembled layer of surfactant molecules (micelles) along the interface between the two phases. The spontaneous self-assembly of the micelle is driven by the thermodynamic tendency to minimize the surface tension between the water and the oil in the presence of the amphiphile (Hoar and Shulman, 1943). 

The effect of electrolyte addition to oscillatory behaviour has also been considered in [235]. The disappearance of structural transition upon electrolyte addition was attributed to its electrostatic origin. The viscosity of the film did not differ much from that of the bulk solution in the case when micelles determined the structuring of the amphiphile surfactant molecules. It is worth to note that the length scale of the oscillations was large, about 10 nm and even reached about 50 nm. 

Mesoporous silica could also be prepared using nonionic amphiphilic surfactants with a polyethylene oxide... 

In a detailed study, mesostructured zirconia has been prepared by using various amphiphilic surfactants with different headgroups (anionic and nonionic) and different tail lengths (1-18 carbons) as templates. Removal of snrfactants leads to the loss of structural order and a decrease ofthe siuface area. However, the presence of phosphates and snlfates in the walls may improve the stability. 

Wang, S.S., Chen, Y.T. and Chou, S.W. (2005) Inhibition of amyloid Hbril formation of beta-amyloid peptides via the amphiphilic surfactants. Biochim Biophys Acta, 1741, 307-13. 

The Krafft point can be defined as the temperature T above which the amphiphile (surfactant) solubility in water greatly increases [3], The reason is that the water solubility of the amphiphile, which increases with temperature, reaches the amphiphile critical micelle concentration (Cm in Figure 3.6). When the solubility curve is above Cm the dissolved amphiphile forms micelles and the amphiphile... 

Amphiphilic surfactant molecules form spherical or nearly spherical aggregates called micelles, above a certain critical concentration, known as the critical micellar concentration (cmc) and above a critical temperature, called Kraft temperature [4,93]. The size of the micellar aggregates is usually 1-10 nm and the aggregation number, l.e., the number of surfactant molecules per micelle, ranges from 20 to 200. The structure of a typical cationic micelle is shown schematically in Fig. 

The 1980s were certainly a period of reaching a general consensus about one important aspect of microemulsions, namely that of thermodynamic stability. It was also a period when we obtained increasing evidence for its microstructure. It is striking that authors then normally found it important to stress what they meant by the term microemulsion . Thus, the first sentence of many papers reads like Microemulsions are thermodynamically stable fluid mixtures of water, oil, and amphiphiles/surfactants . Normally, we do not need to emphasise what we mean with a concept so this practice points to a previous confusion and a need to take a stand in a controversial issue. 

Vegetable oils and natural fats are traditional raw materials for the production of soaps and other surfactants. Coconut oil, palm and palm kernel oil, rape oil, cotton oil, tall oil, as well as the fats of animal origin (tallow oil, wool wax), present renewable raw sources. Linear paraffins and olefins (with terminal or internal double bond), higher synthetic alcohols, and benzene are fossil sources for surfactant production which are obtained from oil, natural gas and coal. Other auxiliary materials are required to construct amphiphilic surfactant structure, such as ethylene oxide, sulphur trioxide, phosphorous pentaoxide, chloroacetic acid, maleic anhydride, ethanolamine, and others. 

Penetration systems at the air-water interface in which a dissolved amphiphile (surfactant, protein) penetrates into a Langmuir monolayer are interesting models for a better understanding of various complex processes. Most of all, penetration systems can simulate properties of biological membranes typically comprised of lipids mixed with proteins. First penetration experiments have been described by Schulman and Hughes in 1935 [110]. In the... 

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