ma7b02550_si_001.pdf (1.46 MB)
Exchange Kinetics for a Single Block Copolymer in Micelles of Two Different Sizes
journal contribution
posted on 2018-03-13, 14:49 authored by Dan Zhao, Yuanchi Ma, Timothy P. LodgeThe effect of micellar size on the
chain exchange kinetics in spherical
micelles consisting of poly(methyl methacrylate)-block-poly(n-butyl methacrylate) (PMMA-b-PnBMA) in a mixture of ionic liquids (1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI], and 1-butyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide, [BMIM][TFSI]) was investigated
using time-resolved small-angle neutron scattering (TR-SANS). Two
spherical micelles with different core sizes were prepared from a
single block copolymer by using different protocols. In one case the
micelles were formed in the presence of a cosolvent, while in the
other a polymer thin film was directly dissolved in the ionic liquid.
Interestingly, the micelle core size prepared from the latter method
is ∼30% larger than that obtained in the former case. TR-SANS
experiments reveal that the rate of single chain exchange in the micelles
with a larger core size is slowed down by ∼3 times compared
to the smaller core radius. This can be possibly attributed to the
smaller interfacial area per chain, and larger corona density, for
micelles with a larger core dimension. These geometrical factors can
potentially lead to changes in both the attempt time and activation
barrier for chain expulsion during the unimer exchange process. Our
results clearly suggest that, in addition to the molecular characteristics
of the block copolymer and solvent, the geometrical structure of the
micelle plays an important role in the unimer dynamic exchange processes
in block copolymer micelles.