K. Schillen et al., Characterization of polyisoprene-b-poly(methyl methacrylate) diblock copolymer micelles in acetonitrile, J PHYS CH B, 103(43), 1999, pp. 9090-9103
In acetonitrile, polyisoprene-b-poly(methyl methacrylate) (PI-PMMA) diblock
copolymers form starlike micelles with a dense core of the insoluble PI bl
ocks and a soft solvent-swollen corona of the soluble PMMA blocks. Static a
nd dynamic light scattering experiments in combination with viscosity measu
rements show that these micelles behave hydrodynamically as hard spheres. T
he block copolymers are labeled at the block junction, with a single fluore
scent dye, either a donor chromophore (phenanthrene) or an acceptor chromop
hore (anthracene), These dyes are confined to the interface during self-ass
embly. Fluorescence energy-transfer experiments on molecularly mixed micell
es of donor- and acceptor-labeled copolymers provide a core radius of 7.6 /- 0.8 nm and a number-average aggregation number (N-n(agg)) Of 98 +/- 22 u
nder the assumption that the energy transfer takes place on a surface of a
sphere. Simulations in terms of a Helfand-Tagami junction distribution prof
ile confirm that the core-corona interface of the PI-PMMA micelles is thin
(ca. 0.9 nm) and that almost all of the energy transfer occurs within a nar
row interfacial region. From the static light scattering measurements of th
e mixed micelles a weight-average aggregation number (N-w(agg)) Of 127 +/-
6 is obtained. The ratio N-w(agg)/N-n(agg) = 1.3 agrees with size polydispe
rsity of the micelles obtained from the analysis of dynamic light scatterin
g data. The experimental corona thicknesses are in good agreement with thos
e calculated from expressions describing starlike block copolymer micelles.