Structure and Interactions of Block Copolymer Micelles of Brij 700 Studied by Combining Small-Angle X-ray and Neutron Scattering

Abstract

Spherical micelles of the diblock copolymer/surfactant Brij 700 (C(18)EO(100)) in water (D(2)O) solution have been investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS and SANS experiments are combined to obtain complementary information from the two different contrast conditions of the two techniques. Solutions in a concentration range from 0.25 to 10 wt % and at temperatures from 10 to 80 degrees C have been investigated. The data have been analyzed on absolute scale using a model based on Monte Carlo simulations, where the micelles have a spherical homogeneous core with a graded interface surrounded by a corona of self-avoiding, semiflexible interacting chains. SANS and SAXS data were fitted simultaneously, which allows one to obtain extensive quantitative information on the structure and profile of the core and corona, the chain interactions, and the concentration effects. The model describes the scattering data very well, when part of the EO chains are taken as a "background"contribution belonging to the solvent. The effect of this becomes non-negligible at polymer concentrations as low as 2 wt %, where overlap of the micellar coronas sets in. The results from the analysis on the micellar structure, interchain interactions, and structure factor effects are all consistent with a decrease in solvent quality of water for the PEO block as the theta temperature of PEO is approached.

Small-Angle Neutron Scattering on a Core−Shell Colloidal System: A Contrast-Variation Study

“…Smoothing of the coreshell interface in eq 5 has been included in modeling similarly structured particles. 29,36,41,43 Instead of opting for a more complex scattering length density profile, which inevitably introduces more adjustable parameters, we retain a homogeneous core but with F core ) 1.0 × 10 -4 nm -2 , because this is sufficient to obtain reasonably accurate fits to the scattering curves over the whole concentration range.…”

Novel pH-Responsive Nanoparticles

“…The micellar structure and properties of similar surfactants have been extensively studied earlier. [25][26][27][28][29][30][31][32][33] For all cases, a concentration of surfactant used for nanoparticles preparation was substantially above the cmc value (cmc ) 2.9 × 10 -3 %) reported for Brij 98. 34 Our surface tension measurements by Wilhelmy plate method give a lower cmc value (1.0 × 10 -3 %).…”

Surfactant or block copolymer micelles? Structural properties of a series of well-defined n-alkyl–PEO micelles in water studied by SANS

“…Sommer et al 31 have extensively studied the structure of Brij700 by using SANS and SAXS. They found a core radius of R c ¼ 15-17Å and an aggregation number of N agg ¼ 30 in very good agreement with the present results.…”

“…We included recent experimental data found for poly(ethylene oxide)-mono-n-alkyl ethers C n -PEO. 30,31,57,58 In order to exclude any effects of the hydrophilic block on the aggregation number N agg was scaled by N PEO 0.51 which was found above to be a reasonable description of the PEO length on N agg . We observe that N agg systematically increases with increasing n. The system almost reveals the characteristic n 2 dependence for the aggregation number that is denoted by the solid line in Fig.…”