Surfactants and Micelles

The production of organic polymeric particles in tire size range of 30-300 nm by emulsion polymerization has become an important teclmological application of surfactants and micelles. Emulsion polymerization is very well and extensively reviewed in many monographs and texts [67, 68], but we want to briefly illustrated tire role of micelles in tliis important process. 

Our results for HOC partitioning in the presence of sorbed surfactant and micelles demonstrate that large differences can exist in the HOC sorption capacity of surfactant aggregates in micellar versus sorbed forms. This can be seen quite readily by calculating Kss values as a function of surfactant dose from the experimental KD values. The distribution coefficient defines the HOC mass balance and can be expressed as ... 

The available data on the effects of surfactants and micellization on the hydrolysis of carboxylic esters are compiled in Table 5. 

After cyclodextrins and co-solvents, other approaches can be applied including the use of surfactants and micelle forming agents. Surfactants can be classified as amphoteric (lecithin), non-ionic (Tween 80 or Cremophor EF) or ionic (sodium lauryl sulfate or sodium palmitate). Cremophor is a polyoxyethylenated castor oil derivative which is a common solubilizing excipient in a number of formulations including those for paclitaxel, propofol, teniposide and clanfenur... 

The addition of various surfactants and micelle forming agents on the biphasic hydroformylation of olefins was also considered as a tool for enhancement of the reaction rate. The relation between the extent of emulsification of the reaction mixture and the performance of hydroformylation reaction was also investigated. Mass transfer effects in biphasic hydroformylation of 1-octene in the presence of cetyltri-methylammoniumbromide (CTAB), was studied by Lekhal etal. [33], A mass-transfer model based on the Higbie s penetration theory was proposed to predict the rate of hydroformylation in a heterogeneous gas-liquid-liquid system under... 

At lower surfactant concentrations (line b) regions of phase separation appear. In such a phase-separated state there is a sequence of equilibria between phases, commonly referred to as Winsor equilibria [13,23]. In point A two macroscopic phases are formed. These are a microemulsion of composition B and an aqueous solution containing dissolved surfactant and micelles with solubilized hydrocarbon. The volumes of these macroscopic phases can be estimated in the usual way by applying the lever rule with a correction for the densities of these phases. In such a state of separation into two macroscopic phases, the equilibrium between the microemulsion and the aqueous solution is referred to as the Winsor II (WII) equilibrium. 

Karaborni S and O Connell J P 1993 Molecular dynamics simulations of model chain molecules and aggregates including surfactants and micelles Tenside 30 235-42... 

Flic literature on surfactants and micelle formation is extensive. 

Of all the catalyst systems studied, Rh-TPPTS is the most suitable and commercially proven catalyst system for biphasic hydroformylation. Several modifications of the water-soluble catalysts using co-solvents [15], surfactants and micelle-forming reagents [16], a supercritical C02-water biphasic system [17], supported aqueous-phase catalysis [18], and catalyst-binding ligands (interfadal catalysis) [19] have been proposed to overcome the lower rates observed in biphasic catalysis due to poor solubilities of reactants in water (see Sections 2.2.3.2 and 2.3.3.3). So far, endeavors have been centered on innovating novel catalyst systems from the viewpoint of efficient catalyst recycle and rate enhancement, but limited information is available on the kinetics of biphasic hydroformylation. 

The on rate constant, /c+, is diffusion-controlled and depends little on surfactant and micelle size (cf. Table 19.5). The off rate constant, on the other hand, is strongly dependent on alkyl chain length, micelle size, etc. Because of the co-operativity in micelle formation there is a very deep minimum in the size distribution curve. This leads to a two-step approach to equilibrium after a perturbation. In a fast step, quasiequilibrium is reached under the constraint of a constant total number of micelles. The redistribution of unimers between abundant micelles is a fast process. In order to reach a true equilibrium, the number of micelles must change. Because of the stepwise process, this also involves the very rare intermediate micelles. Therefore, this process is slow. 

FIGURE 14.12. Polymer-surfactant interactions are important in many areas of polymer science and technology, especially emnlsion polymerization. In snch processes surfactants and micelles perform several dnties snch as emulsification of monomers (a), solnbihzation of growing oUgomeric free radical chains (b), and stabilization of growing and final polymer particles (c). 

Fig. 3. The effect of salt concentration on the partitioning of surfactant and micelle formation.

Substances bearing hydrophobic parts such as PSS, PMBQ, styrene or surfactants and micelles form complexes that are very dense or compact The stability is often low. 

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