Micelles stability

Soap. A critical ingredient for emulsion polymerization is the soap (qv), which performs a number of key roles, including production of oil (monomer) in water emulsion, provision of the loci for polymerization (micelle), stabilization of the latex particle, and impartation of characteristics to the finished polymer. 

Different type of reaction system containing organic solvent can be classified in a simple way. To accomplish this we first distinguished between microaqueous organic systems with a continuous organic phase, then reversed micelles stabilized with surfactant and a liquid-liquid biphasic system in which distinct organic and aqueous phase are mixed. The latter medium is discussed in this paper. 

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

The reverse micelles stabilized by SDS retard the autoxidation of ethylbenzene [27]. It was proved that the SDS micelles catalyze hydroperoxide decomposition without the formation of free radicals. The introduction of cyclohexanol and cyclohexanone in the system decreases the rate of hydroperoxide decay (ethylbenzene, 363 K, [SDS] = 10 3mol L [cyclohexanol] =0.03 mol L-1, and [cyclohexanone] = 0.01 mol L 1 [27]). Such an effect proves that the decay of MePhCHOOH proceeds in the layer of polar molecules surrounding the micelle. The addition of alcohol or ketone lowers the hydroperoxide concentration in such a layer and, therefore, retards hydroperoxide decomposition. The surfactant AOT apparently creates such a layer around water moleculesthat is very thick and creates difficulties for the penetration of hydroperoxide molecules close to polar water. The phenomenology of micellar catalysis is close to that of heterogeneous catalysis and inhibition (see Chapters 10 and 20). 

Thermoresponsive polymeric micelles with PIPAAm block copolymers can be expected to combine passive spatial targeting specificity with a stimuli-responsive targeting mechanism. We have developed LCSTs of PIPAAm chains with preservation of the thermoresponsive properties such as a phase transition rate by copolymerization with hydrophobic or hydrophilic comonomers into PIPAAm main chains. Micellar outer shell chains with the LCSTs adjusted between body temperature and hyperthermic temperature can play a dual role in micelle stabilization at a body temperature due to their hydrophilicity and initiation of drug release by hyperthermia resulting from outer shell structural deformation. Simultaneously, micelle interactions with cells could be enhanced at heated sites due... 

Hill, R. J. and Wake, R. G. 1969. Amphiphile nature of -casein as the basis for its micelle stabilizing properties. Nature 221, 635-639. 

As with normal hydrocarbon-based surfactants, polymeric micelles have a core-shell structure in aqueous systems (Jones and Leroux, 1999). The shell is responsible for micelle stabilization and interactions with plasma proteins and cell membranes. It usually consists of chains of hydrophilic nonbiodegradable, biocompatible polymers such as PEO. The biodistribution of the carrier is mainly dictated by the nature of the hydrophilic shell (Yokoyama, 1998). PEO forms a dense brush around the micelle core preventing interaction between the micelle and proteins, for example, opsonins, which promote rapid circulatory clearance by the mononuclear phagocyte system (MPS) (Papisov, 1995). Other polymers such as pdty(sopropylacrylamide) (PNIPA) (Cammas etal., 1997 Chung etal., 1999) and poly(alkylacrylicacid) (Chen etal., 1995 Kwon and Kataoka, 1995 Kohorietal., 1998) can impart additional temperature or pH-sensitivity to the micelles, and may eventually be used to confer bioadhesive properties (Inoue et al., 1998). 

However, Yokoyama et al. (1994) reported that a ratio between the chemically conjugated and physically entrapped ADR (i.e., DOX) was not determined, and considerable amounts of adriamycin derivatives formed and were incorporated in the micelles. Yokoyama et al. (1998) quantitatively measured the ADR incorporated in the inner core using the improved synthetic method, and analyzed the effects of the ADR contents (both by chemical conjugation and physical entrapment) on micelle stability andn vivo antitumor activity. The copolymer used by Yokoyama et al. (1998) was polyethylene glycol)-fepoly(aspartic acid) block copolymer (PB P(Asp)). The chemical conjugation and physical entrapment methods can be referred to in the earlier section of preparation of polymeric micelles. 

Yokoyama, M., G S. Kwon, T. Okano, Y. Sakurai, M. Naito, and K. Kataoka. 1994. In uencing factors on in vitro micelle stability of adriamycin-block copolymer conjugat sControl. Rel28 59-65. 

Surfactants fulfil many functions, such as detergency, micelle stabilization, interfacial tension reduction, wetting, and so on. In hydrocarbons, however, surfactants are not capable of lowering the surface tension, because these solvents... 

Hydrolysis of the casein micelle-stabilizing K-casein by the action of selected acid proteinases (rennets), and the resultant slow quiescent aggregation of the destabilized micelles in the presence of calcium ions ( 3 mM) at 30-36°C (e.g., for most rennet-curd cheeses such as Cheddar, Mozzarella and Gouda)... 

Finally a better understanding of the effects of temperature, organic modifier and pressure on micelle stability is important if micellar chromatography is to develop and become an accepted method within the area of chromatography. 

Husseini GA, Christensen DA, Rapoport NY, and Pitt GW. Ultrasonic release of doxorubicin from Pluronic P105 micelles stabilized with an interpenetrating network of 7/,7/-diethylacrylamide. J. Control. Rel. 2002 83 303-305. 

Reversed Micelle Stabilized Nickel Boride The borohydiide reduction of a nickel salt in the presence of reversed micelles provides a convenient method for the preparation of very small nickel boride... 

As shown by the data in Fig. 12.4 these micelle stabilized catalysts were considerably more active for alkene hydrogenation than the P-2 nickel borides. The hydrogenation run using a preformed P-2 catalyst in a reversed micelle medium proceeded at a faster rate than the reaction run over P-2 nickel boride in... 

The borohydride reduction of nickel decanoate in cyclohexane also produced a reversed micelle stabilized nickel boride cateilyst.37 The most active catalyst was formed using a 3 1 BH4 Ni ratio. This gave a catalyst that was about as active as the P-2 catalyst for alkene hydrogenation. The use of other BH4 Ni ratios gave less active catalysts. 

Reversed micelles stabilize a nanometer-sized aqueous environment within the surfactant aggregate, which is dispersed in a fully nonhydrous or a semipolar solvent. In this micellar core environment we may dissolve metal salt solutions that react to the extent of the available reactants. 

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