Time-resolved specular and off-specular neutron reflectivity measurements on deuterated polystyrene and poly(vinyl methyl ether) blend thin films during dewetting process

We performed time-resolved specular and off-specular neutron reflectivity measurements on blend thin films 42 and 98 nm thick of deuterated polystyrene and poly(vinyl methyl ether) during dewetting process induced by the phase separation in two phase region using a time-of-flight neutron reflectometer. In the specular measurements we found that the phase separation directed to the depth direction occurred near the air interface as well as near the Si substrate during the incubation period before dewetting. In addition we also found that the phase separation occurred asymmetrically at the two interfaces and inhomogeneously in the film plane, showing that the dewetting was induced by the composition fluctuation mechanism. Off-specular reflectivity was analyzed, for the first time, to evaluate kinetics of structure formation in the film plane during the dewetting process. We found in the analysis that the droplets formation in micrometer scale occurred in the late stage of dewetting.