Micelles multimolecular

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

Note 2 The mesomorphic character of a lyotropic mesophase arises from the extended, ordered arrangement of the solvent-induced micelles. Hence, such mesophases should be regarded as based not on the structural arrangement of individual molecules (as in a non-amphiphilic or a thermotropic mesophase), but on the arrangement within multimolecular domains. 

The addition of large linear blocks to dendrons with opposite polarity creates a desymmetrized structure predisposed to sequester insoluble components by aggregation rather than intramolecular hydrogen-bonding. Amphiphilic, linear-dendritic diblock (AB) and triblock (ABA) copolymers self-assemble into multimolecular micelles with CMC values that are well below those of low molecular weight surfactants. Typically, a hydrophilic linear block such as PEG is attached to the focal point... 

This last problem is perhaps not strictly within the realm of photochemistry. It is however so important potentially that it cannot be overlooked on grounds of arbitrary separations between different branches of scientific research (perhaps the expression of interdisciplinary approach would best describe it). A few pages will therefore be devoted to the science and technology of artificially organized molecular systems such as monomolecular and multimolecular layers, micelles and spatially restricted environments like zeolites and since we reach here another of the frontiers of photochemistry, section 8.4 in the final chapter is devoted to these systems. 

The structure of the lyotropically mesomorphous lattice is made up of multimolecular units called mesoaggregates. These are surrounded by an intervening liquid. Lyotropic mesomorphism is therefore closely related to the tendency of lipids to accumulate at interfaces. The surface activity is a consequence of the same dualistic polar/non-polar molecular structure that causes the formation of micelles in solutions of association colloids (I, 2, 3, 4, 5, 6). 

From the data presented in Chapter 10, it becomes evident that the extreme longevity of the artificial surfactant-stabilized microbubbles described therein is, in part, related to their continuous interaction with the simultaneously formed mixed micelle population in the saturated surfactant solution. More specifically, the surfactant-stabilized microbubbles produced by mechanical agitation of saturated solutions of either CAV-CON s Filmix 2 or Filmix 3 apparently undergo a cyclical (or reversible) process of microbubble formation/coalescence/fission/disappearance, where the end of each cycle is characterized by a collapse of the lipid-coated microbubbles into large micellar structures (i.e., rodlike multimolecular aggregates), only to re-emerge soon after as newly formed, lipid-coated microbubbles (see also below). 

Critical micelle concentration. The concentration in solution at which a surface-active agent forms multimolecular aggregates which are in kinetic equilibrium with monomer. 

Tsitsilianis et al. recently published [245] preliminary results on the micelliza-tion behavior of anionically synthesized amphiphilic heteroarm star copolymers with polystyrene and poly(ethylene oxide) branches in THF and water. The former solvent is not very selective for one of the segments whereas the latter is strongly selective for PEO. The apparent molecular weights found for the micelles in THF were two orders of magnitude larger than the ones measured for the unimers. By increasing concentration an increase in the depolarization ratio was observed supporting the conclusion that multimolecular micelles are formed by this kind of miktoarm star copolymer. 

Nanospheres were created by the following procedure multimolecular micellization, followed by core polymerization of block copolymer of poly(ethylene glycol) (PEG) with poly(lactic... 

Further, the ability to synthesize random copolymers with various hydrocarbon monomers allows the anchor-soluble balance to be tuned while maintaining solubility even with high incorporations of hydrocarbon comonomers [29]. Because of the amphiphilic nature of such copolymers, it was predicted that these materials would selfassemble into micelles consisting of a highly fluorinated corona segregating the lipophilic core from the compressed CO2 continuous phase. Thus, PFOA-F-PS block copolymers were synthesized via controlled free-radical techniques (Fig. 9.3), and it was confirmed (by smaU-angle neutron scattering) that these copolymers spontaneously assemble into multimolecular micelles in solution [40]. In addition to amphiphilic materials, which physically adsorb to the surface of polymer particles in dispersion polymerizations, fluorinated acrylates can be utihzed as polymerizable comonomers in the stabilization of C02-phobic polymer colloids [41]. 

Figure 11 Coexistence of uni- and multimolecular micelles at concentration of PS7-P2VP7 0.03 g I"" (HCI, pH 1) before (a) and after metallization with Pd (b, c). Metallization improves AFM contrast, and thus the aggregation number can be directly estimated. For example, the structure marked by the yellow arrow corresponds to a tetramer with about 28 P2VP arms, the green arrow corresponds to a trimer with about 21 P2VP arms, and the red arrow shows a unimer with seven P2VP arms. Reprinted from (a) Gorodyska, G. Kiriy, A. Minko, S. etal. Nano Lett. 2003, 3,365. (b) Kiriy, A. Gorodyska, G. Minko, S. etal. Macromolecules 2003, 36, 8704.237...

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