EQUILIBRIUM SEGMENT DENSITY DISTRIBUTION OF A DIBLOCK COPOLYMER SEGREGATED TO A POLYMER-POLYMER INTERFACE

Utilizing neutron reflectometry, we have determined the segment densit y (volume fraction) profiles of the deuteriopolystyrene (dPS) block of a diblock copolymer of poly(styrene-d8-b-2-vinylpyridine) (dPS-PVP) s egregating to the interface between the homopolymers PS and PVP as a f unction of phi(infinity), the volume fraction of diblock copolymer rem aining in the host homopolymer after annealing the specimens to reach the equilibrium segregation. These segment density profiles were used to determine the interfacial excess (zi), which was found to be in go od agreement with direct measurements of zi using forward recoil spec trometry. The interaction parameter chi(PS-PVP) was established from t he best fit of a self-consistent mean field (SCMF) theory to the measu red segregation isotherm, i.e., zi versus phi(infinity). With this ch i(PS-PVP), the SCMF theory can reproduce the experimental volume fract ion profile of the dPS block accurately except very close to the inter face; the measured profile is broader at the interface as compared to the predicted profile. This excess broadening is observed for all phi( infinity)'s and tends to be enhanced as zi increases. We believe that most of the interface broadening is due to the ''roughening'' of the equilibrium interface encouraged by the decrease in interfacial tensio n accompanying the copolymer segregation. Excellent agreement between the measured profiles and the theoretical predictions of SCMF theory a t various phi(infinity)'s is found if a Gaussian convolution is used t o represent the effect of the interfacial roughness.