Micelles density

Transitions may occur in block copolymer/C02 systems, due to change in temperature and pressure. Subsequently a critical micelle density (CMD), analogous to the critical micellisation concentration (CMC) was found. The existence of a CMD was first argued by McClain et al. (47), who observed a transition from aggregates to unimers for the PS-6-PFOA/CO2 system, as solvent density was increased. Further evidence for the CMD was provided by Triolo et al. (50-52) and Zhou and Chu (53, 54). 

Samulski and J. M. DeSimone, Critical micelle density for the self-assembly ofblock copolymer surfactants in supercritical carbon dioxide, iongmihr 16(2) 416 (2000). 

Next, it was demonstrated that the CNT presents limitations when the nuclei size falls into the nanometric range [81]. However, the alternative nucleation models present a significant complexity therefore CNT is commonly used to provide a qualitative estimation of nncleation in nanoporous foams the feamres proposed by Spitael et al. currently are stiU widely accepted. In addition, it is well known that nanoporous polymer requires nuclei densities greater than 10 " nuclei per cubic centimeter of the precursor materials. Therefore initial micelle densities should be higher than this value to produce nanoporous polymers from polymer blends presenting a nucellar nanostructuration, but hopefully these values can be expected even when BCP precursors are blended at low copolymer concentration (eg, <10 wt%). 

Micellar objects and micelle-like domains are induced by low amounts of MAM (5-20 wt%) and presented a core-shell structure, with the core identified as PMMA and the shell as PBA surrounded by PMMA chains of the copolymer miscible with the PMMA matrix. Micelle density seemed to be constant in the solid unfoamed precursors with values of approximately 4-4.5 x 10 " micelles/cm. Moreover, the apparent size of the micelles varies from 20 nm in 95/5 PMMA/MAM blends to 50 nm in 80/20 PMMA/MAM blends, with the core size approximately one-third of the micelle size (Fig. 9.11). This evolution of the nanostructure was noticed as unexpected and related to the processing conditions during the self-assembly of the nanostructuration, probably out of equilibrium. In addition, it was noticed that the injection procedure induces an orientation or even an elongation of the micellar-like domains in the injection direction (Fig. 9.12). On the contrary, 25/75 PMMA/MAM blends showed no influence of the injection process on the orientation of the nanostructure, with poorly defined lamella of 20-30 nm apparent thickness. 

Sallach RE, Wei M, Biswas N, Conticello VP, Lecommandoux S, Dluhy RA, Chaikof EL (2006) Micelle density regulated by a reversible switch of protein secondary structure. J Am Chem Soc 128 12014-12019... 

U Itracentrifugation Micelle density, molecular weight (Z average), micelle/unimer weight ratio... 

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