Micelle assembly

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. 

Time-resolved in situ Small Angle Neutron Scattering (SANS) investigations have provided direct experimental evidence for the initial steps in the formation of the SBA-15 mesoporous material, prepared using the non-ionic tri-block copolymer Pluronic 123 and TEOS as silica precursor. Upon time, three steps take place during the cooperative self-assembly of the Pluronic micelles and the silica species. First, the hydrolysis of TEOS is completed, without modifications of the Pluronic spherical micelles. Then, when silica species begin to interact with the micelles, a transformation from spherical to cylindrical micelles takes place before the precipitation of the ordered SBA-15 material. Lastly, the precipitation occurs and hybrid cylindrical micelles assemble into the two-dimensional hexagonal structure of SBA-15. 

Shown in Figure 1 are the principal schemes for micelle and liposome formation and loading with various reporter moieties that might be covalently or noncovalently incorporated into different compartments of these particulate carriers. Although micelles may be loaded with a contrast agent only into the core in the process of micelle assembly, liposomes may incorporate contrast agents in both the internal water compartment and the bilayer membrane. 

At higher concentrations, micelles assemble in turn, to form hexagonal or cubic phases while longer chains or multi-chain compounds afford lamellar phases in which the amphiphilic derivative is arranged in parallel bilayers, separated by water. The succession of mesophases depending on temperature and concentration of the amphiphile can be visualized in a phase diagram (Fig. 3 c). 

Assembly of a virus Assembly of ribosomes Formation of micelles Assembly of the cell Surface metal coating... 

Keenan, 1975 Neville et al., 1981 Watters, 1984 Virk et al., 1985), the presumption is that the formation of casein micelles is orchestrated with the transport of ions, the phosphorylation and glycosy-lation of the caseins, and lactose synthesis, such that the intravesicular ionic environment and casein concentration change continuously during the 20 min or so required for micelle assembly. Patton and Jensen (1975) observed, in electron micrographs, the same density of micellar particles in the alveolus as in mature vesicles, suggesting that, by this stage, the vesicular concentrations are virtually identical to those in the aqueous phase of milk. 

Tables VI and VII present some representative data on the binding constants and partition coefficients reported for the interaction of selected solutes with different surfactant micellar systems. The strength of the association of solutes with surfactant micelle assemblies is dictated by the net electrostatic, hydrogen-bonding, and/or hydrophobic interactions possible for a given solute - micelle combination under the prevailing experimental conditions.

Fig. 6 Self-assembly of ABA triblock copolymers under different conditions, (a) Star-like micelle, (b) Flower-like micelle, (c) Micelle assembly...

C for 12 h to obtain free mesoporous siliea nanorods (Fig. P-8). Even when there is confinement, the spherical micelles assemble in a close packed way inside the nanosized channels of the template the pore size of the micelles increases from 13nm to 20nm on confinement. This is attributed to the soft nature of the template and also the favorable van der Waals forces. The concentration of the copolymer affects the micelle size. For a concentration of 20 wt% copolymer, the pores are uniform throughout the nanorods. However, at higher or lower concentration of the copolymer, the pores are not uniformly distributed. The interaction between the matrix of the template and the copolymer has been attributed as the reasons for this trend. 

Figure 25 Assembly of DNA-brush copolymers into micelles with spherical or cylindrical morphologies. Amphiphile structures are represented as cones for each respective motphology, with the hydrophobic domain highlighted in red. TEM images of (a) 25-nm spherical micelles assembled from initial DNA-brush copolymers (b) cylindrical morphology formed following DNAzyme addition to spheres (c) spherical micelles (green) formed after the addition of hi to cylinders. Reproduced with permission from Chien, M.-P. Rush, A. M. Thompson, M. P. etal. Angew. Chem. Int. Ed. 2010,49, 5076-5080. 2...

Li, Z., Zhang, Y, Fullhart, P, and Mirkin, C. A. 2004. Reversible and chemically programmable micelle assembly with DNA block-copolymer amphiphiles. Nano Lett. 4 1055-1058. 

Nunes SP et al. Switchable pH-responsive polymeric membranes prepared via block copolymer micelle assembly. ACS Nano 2011 5(5) 3516-3522. 

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