SANS studies of confined diblock copolymers in microemulsions

Using small angle neutron scattering (SANS) polymers were studied as additives in microemulsions. Usually, one assumes no or small confinement, which is expressed by the ratio of the polymer size R-g and the domain size d. For amphiphilic diblock copolymers, an increased surfactant efficiency and a more rigid surfactant membrane were observed. The sensitivity of the diblock copolymer effect on polymer concentration agreed with theoretical predictions. The current study is focused on medium and higher confinement of diblock copolymers. A computer simulation predicted elevated sensitivities for medium confinement and a reversed behaviour for high confinement. Experimentally, we found evidence for the reversal between medium and high confinement. The correlation length, which is proportional to the membrane rigidity, increased or decreased depending on the level of confinement. This result supports the interpretation that at high confinement the anchored diblock copolymer and the free homopolymer cannot be distinguished anymore. (c) 2006 Elsevier B.V. All rights reserved.