Order−Disorder Transition and Critical Micelle Temperature in Concentrated Block Copolymer Solutions

Abstract

The phase behavior of symmetric styrene-isoprene (SI) diblock copolymers in selective solvents in the vicinity of the order-disorder transition (ODT) was investigated by small-angle neutron scattering (SANS). Particular emphasis is placed on the region just above the ODT, where a disordered phase of micelles is observed. To understand morphological changes in more detail, one of the blocks is deuterated, i.e., PS-dPI and dPS-PI, and the scattering length density (SLD) of the solvents used were identical to the SLD of the corona chains. Two approaches for the analysis of SANS data were taken: the generalized indirect Fourier transformation (GIFT) and direct model fitting with relevant form and structure factors. With increasing temperature, the micellar aggregation number decreases, and the core radius is roughly maintained by the increased solvent swelling of the core. The critical micelle temperature (cmt) is experimentally described in the present study by an abrupt decrease in the size, aggregation number, and volume fraction of micelles. The micelles were found to dissociate into free chains approximately 20-30°C higher than the T ODT, and the cmt is found to be quite close to the mean-field spinodal temperature TS. A mean-field temperature, TMF, is located by the crossover temperature from the linear behavior of Imax -1 vs T -1 plot, and the structure factor above the experimentally determined TMF is also found to be in good agreement with the Leibler-Landau-type mean-field theory. We examined two different ODTs: body-centered cubic lattices to disorder and hexagonal cylinders to disorder, with similar results in both cases.

Effects of Intermicellar Interactions on the Dissociation of Block Copolymer Micelles: SANS and NMR Studies

“…Here we choose a well‐characterized block copoly­mer micelle systems, polystyrene‐ block ‐polyisoprene in decane, to explore the influence of polymer concentration on the dissociation of block copolymer micelles. Previous studies of the dissociation of PS–PI diblock copolymer micelles in organic solvents have focused on either dilute solutions or highly concentrated ones where the micelles were in an ordered state . With increasing concentration of non‐ionic micelles, the intermicellar interaction increases, as long as no phase transition takes place.…”

“…Previous studies of the dissociation of PS-PI diblock copolymer micelles in organic solvents have focused on either dilute solutions [ 9 ] or highly concentrated ones where the micelles were in an ordered state. [ 29 ] With increasing concentration of nonionic micelles, the intermicellar interaction increases, as long as no phase transition takes place.…”

Synthesis of amine‐functionalized block copolymers for nanopollutant removal from water

“…Block copolymers self‐assemble into diverse morphologies depending on the relative fractions of the hydrophobic and hydrophilic blocks . Different polymer‐solvent interactions and properties of solvents are known to control the structure of the micelles and their ordered packing …”

Synthesis of amphiphilic block copolyamines via click reaction

“…In the synthesized polymers the hydrophobic styrene block was kept constant while changing the nature of amine functional groups. Polymer-solvent interactions and properties of solvents are known to control the structure and packing [38,39].…”