Aggregate, polymer-micelle

A polymer prepared in the presence of a secondary force often possesses a structure different from that obtained in solution. Template polymerization is a typical example. Micelles and polymer micelles are formed under conditions of thermodynamic equilibrium, so that the structure of these aggregates are always quite fluid. If the aggregate structure is immobilized by polymerization, they will provide better models of enzymes. 

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. 

Note 3 A polymer composed of molecules that have rigid rod-like groups or chains may form LC mesophases in solution under suitable conditions. These are sometimes described as lyotropic but, as the solvent does not induce the formation of aggregates or micelles, this term is not appropriate. 

Self-assembly of polymers in the bulk Polymer micelles, polymero-somes, gelled macromole-cules, nano-tubes, protein fibres/tapes produced by aggregation at low pH, controlled release vehicles, smart delivery systems 50-500 nm Forster and Konrad, 2003 Sanguansri and Augustin, 2006 Dickinson 2006a Graveland-Bikker and de Kruif, 2006 van der Linden, 2006... 

Ito s group [83] reported the micellar polymerization mechanism was operative during the radical polymerization of PEO macromonomers in cyclohexane and water under similar reaction conditions. The reaction medium has an important effect on the polymerization behavior of macromonomers. Cyclohexane was chosen as a nonpolar type of solvent. The polymerization was found to be independent of the lengths of p-alkyl group (R) and the PEO chain in benzene. On the other hand, the rate of polymerization in cyclohexane increased with increasing number of EO units. This may be attributed to the formation of aggregates (micelles) and/or compartmentalization of reaction loci,i.e., polymerization in distinct aggregates (polymer particles). The C12-(EO)14-MA macromonomer polymerized faster in bulk than in benzene but far slower than in water. 

As is being discussed, polymers used to prepare micelles exhibit a LCST that can be deLned as the temperature at which the polymer phase separates (Heskinsand Guillet, 1968). Below the LCST, the polymer/micelle is soluble, but it precipitates at temperatures above the LCST. The diameter of these micelles rapidly rises at temperatures above the LCST, due to hydrophobic interactions that result in the aggregation of the micelles (Kohori et al., 1998). This effect of temperature on size was shown to be reversible, since the micellar architecture was maintained after lowering the temperature below the LCST (Chung et al., 1999). 

We begin here a brief survey of thermodynamic principles that pertain to formation and self assembly of large scale aggregates of molecular units, such as polymers, micelles, vesicles, or similar macromolecules. We follow the exposition of Israelachvily. ... 

Classical emulsion polymerization is divided into three kinetic stages. At the start of the process, the unsaturated monomers are dispersed into small droplets, stabilized with surfactants. Additional surfactant aggregates into micelles. These micelles are very small ( 10nm) relative to monomer droplets ( 1-10 pm). During stage 1 the initial formation of polymer... 

Single polymer micelles were observed at low polymer concentrations in aqueous media whereas at higher concentrations both inter and intrapolymeric aggregation took place. Above the critical solution temperature excimer formation decreased due to disruption of the pyrene aggregates. 

The surface tension of the continuous phase of a polymer emulsion may be used as a measure of the free onulsifier concentration. ITie term free onulsifier is used here to denote surfactant which is dissolved in the aqueous phase rather than being adsorbed on to polymer particles or monomer droplets, or aggregated into micelles. The free emulsifier concentration is widely considered to be a critical variable in the phenomenon of steady-state oscillation in a CSTR and in preventing coagulation during polymoization. 

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