Small-Angle Neutron Scattering Study of Microphase Separation in Thermoassociative Copolymers

Abstract

The morphology of poly(sodium acrylate)-g-poly(ethylene oxide) graft copolymers (PAA-g-PEO) in semidilute solution has been studied by small-angle neutron scattering using a temperature or salting-out effect as trigger for the phase separation of PEO side chains. As soon as the critical conditions are reached, a scattering peak arising from the correlation between the PEO domains is clearly observed. Beyond the critical conditions, e.g., at higher temperature or salt concentration, the magnitude of the fluctuations keeps on increasing while their wavelength or the periodicity of the microdomains remains constant. At the same time, the asymptotic behavior, studied at higher values of the scattering vector q, indicates that PEO side chains undergo a continuous transition from an homogeneous solution of random coils, in the weak segregation regime, to a microseparated two-phase structure with a sharp boundary in the so-called strong segregation regime (corresponding to high temperature and/or salt concentrat...