Characterization of Polyisoprene-b-Poly(methyl methacrylate) Diblock Copolymer Micelles in Acetonitrile

Abstract

In acetonitrile, polyisoprene-b-poly(methyl methacrylate) (PI-PMMA) diblock copolymers form starlike micelles with a dense core of the insoluble PI blocks and a soft solvent-swollen corona of the soluble PMMA blocks. Static and dynamic light scattering experiments in combination with viscosity measurements show that these micelles behave hydrodynamically as hard spheres. The block copolymers are labeled at the block junction, with a single fluorescent dye, either a donor chromophore (phenanthrene) or an acceptor chromophore (anthracene). These dyes are confined to the interface during self-assembly. Fluorescence energy-transfer experiments on molecularly mixed micelles 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 under the assumption that the energy transfer takes place on a surface of a sphere. Simulations in terms of a Helfand-Tagami junction distribution profile 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 narrow interfacial region. From the static light scattering measurements of the 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 polydispersity of the micelles obtained from the analysis of dynamic light scattering data. The experimental corona thicknesses are in good agreement with those calculated from expressions describing starlike block copolymer micelles.

DNA Hybridization in Thermoresponsive Polymer Nanoparticles

“…The DLS data also shows that the size distribution of the nanoparticles is very narrow for all temperatures, with a polydispersity lower than 0.05, calculated from the ratio of the second comulant to the square of the first comulant. [31,32] TEM images of the nanoparticles (Figure 4 A) show that these are very monodisperse with a dry diameter of 129 AE 4 nm (Figure 4 B), which coincides with the core diameter obtained by DLS (in the TEM images the particles are dried and the shell is completely collapsed onto the core, with an expected dried shell thickness of only 0.88 nm, according to the quantities used in the synthesis). The monodispersity of the nanoparticles is also apparent in concentrated dispersions in water, which are strongly opalescent (Figure 4 C).…”

Fluorogenic enzyme-responsive micellar nanoparticles

“…21 Relevant and notable exceptions involve the use of fluorescence energy transfer for studying interfacial regions in the assembly of nanoparticles and micelles. [22][23][24] Here, we demonstrate that in addition to enabling a direct measurement of exceptionally low CAC for micelles, and a geometrical determination of aggregation number, 23,25 FRETlabeled PPAs can be utilized to sensitively monitor micellar nanoparticle response to enzymes. These parameters were determined by analysis of the distance dependence of FRET efficiency within polymeric micelles in which each amphiphile in the assembly is covalently end-labeled with one of two dyes in a pair.…”

Insight into molecular imprinting in precipitation polymerization systems using solution NMR and dynamic light scattering

“…All DLS measurements were carried out at 21°C. The refractive index ( n 0 ) of acetonitrile is 1.344 and the viscosity ( η 0 ) is 0.3741 cP (Schillén et al ., 1999).…”