Polymer-like micelles

A number of examples have been studied in recent years, including liquid sulfur [1-3,8] and selenium [4], poly(o -methylstyrene) [5-7], polymer-like micelles [9,11], and protein filaments [12]. Besides their importance for applications, EP pose a number of basic questions concerning phase transformations, conformational and relaxational properties, dynamics, etc. which distinguish them from conventional dead polymers in which the reaction of polymerization has been terminated. EP motivate intensive research activity in this field at present. 

Mezzasalma S. A., Koper G. J. M. and Shchipunov Yu. A., Lecithin organogel as a binary blend of monodisperse polymer-like micelles. Langmuir 16 (2000) pp. 10564-10565. 

Shchipunov YA, Hoffmann H. Thinning and thickening effects induced by shearing in lecithin solutions of polymer-like micelles. Rheologica Acta. 2000 39(6) 542-553. 

Instabilities that manifest themselves in surfactant and polymeric systems have been considered in an attempted to elucidate the myelin instability. In polymer-like micelles (or wormlike micelles) instabilities have been observed in the directional growth of hexagonal phases in a temperature gradient (30), These instabilities are an example of the Mullins and Sekerloi type (31), In the case of polymer gels, instabilities appear during growth, which resemble a raspberry like texture at the surface. This instability is due to the elastic properties of the gel which is a network of chemically bonded polymers. As the gel swells at the surface it remains anchored to the rest of the unswollen gel and the surface buckles (50). 

Key words Lecithin - phosphatidyl-ethanolamine - self-organization -reverse micelles - polymer-like micelles - organogel - hydrogen bonds - molecular model... 

Fig. 2 Schematic representation of the polymer-like micelle formed by lecithin in the presence of DMFA, FA, water and PE. Various types of molecular arrangement and hydrogen bondings are shown...

Schurtenberger, R, Jerke, G., Cavaco, C. Cross-section structure of cylindrical and polymer-like micelles from small-angle scattering data. 2. Experimental results. Langmuir 1996, 72(10), 2433-2440 and references cited therein. 

J. S. Pedersen, M. Laso, P. Schurtenberger. Monte Carlo study of excluded volume effects in worm-like micelles and semi-flexible polymers. Phys Rev E 54 R5917-R5920, 1996. 

Then we address the dynamics of diblock copolymer melts. There we discuss the single chain dynamics, the collective dynamics as well as the dynamics of the interfaces in microphase separated systems. The next degree of complication is reached when we discuss the dynamic of gels (Chap. 6.3) and that of polymer aggregates like micelles or polymers with complex architecture such as stars and dendrimers. Chapter 6.5 addresses the first measurements on a rubbery electrolyte. Some new results on polymer solutions are discussed in Chap. 6.6 with particular emphasis on theta solvents and hydrodynamic screening. Chapter 6.7 finally addresses experiments that have been performed on biological macromolecules. 

Schurtenberger, P, Scartazzini, R., Magid, L. J., Leser, M. E., and Luisi, P. L. (1990). Structural and dynamic properties of polymer-like reverse micelles. /. Phys. Chem., 94, 3695-701. 

Increasing the concentration of surfactants in water to a level above the CMC leads to the formation of rod-like micelles and, subsequently, liquid crystals [251]. Both liquid crystals and liquid-crystalline polymers [252] have been used as media for small particle generation [253, 254] and have also acted as piezoelectric devices [255]. Of particular interest are metallomesogens, the metal complexes of organic ligands which exhibit liquid crystalline behavior [255],... 

If rj is independent of the shear rate y a liquid is called Newtonian. Water and other low molecular weight liquids typically are Newtonian. If rj decreases with increasing y, a liquid is termed shear thinning. Examples for shear thinning liquids are entangled polymer solutions or surfactant solutions with long rod-like micelles. The zero shear viscosity is the value of the viscosity for small shear rates ij0 = lim,> o tj y). The inverse case is also sometimes observed rj increases with increasing shear rate. This can be found for suspensions and sometimes for surfactant solutions. In surfactant solutions the viscosity can be a function of time. In this case one speaks of shear induced structures. 

Block copolymers self-assemble to form nanoscale organized structures in a selective solvent. The most common structures are spheres, with the insoluble core surrounded by a solvent-swollen corona. In some instances, disk- or worm-like micelles form, and are of particular interest, since the control of their association can lead to a broad range of new applications [1,2]. An important subset of block copolymer micelles are those which contain metal atoms, through covalent attachment or by complexa-tion [3], These structures are interesting because they take advantage of the intrinsic properties of their components, such as the mechanical properties of the polymer micelles and the optical and magnetic characteristics of the metal atoms. Moreover, the assembly permits the control of the uniformity in size and shape of the nanoparticles, and it stabilizes them. 

In spatially evolving multiphase media (e.g., during dissolution of a porous medium, or phase separation in a polymer blend), the mean curvature of the interface between two phases is of interest. Curvature is a sensitive indicator of morphological transitions such as the transition from spherical to rod-like micelles in an emulsion, or the degree of sintering in a porous ceramic material. Furthermore, important physicochemical parameters such as capillary pressure (from the Young-Laplace equation) are curvature-dependent. The local value of the mean curvature K — (1 /R + 1 /Ri) of an interface of phase i with principal radii of curvature Rx and R2 can be calculated as the divergence of the interface normal vector ,... 

For polymers, DT is found to be virtually independent of chain length and chain branching, but it is strongly dependent on polymer and solvent composition [84]. For random copolymers, DT varies linearly with monomer composition block copolymers display more complex behavior [111,214]. For segregated block copolymers like micelles, DT seems to be determined by the monomers located in the outer region (see Fig. 18). For particles, DT appears to be both composition and size dependent [215]. 

Angelico, R., Palazzo, G., Colafemmina, G., Cirkel, P. A., Giustini, M., and Ceglie, A. (1998), Water diffusion and head group mobility in polymer-like reverse micelle Evidence of a sphere-to-rod-sphere transition, J. Phys. Chem. B, 102, 2883-2889. 

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