Structures of P(S-block-BMA) diblock copolymers in thin films

Symmetrical diblock copolymers (P(S(D)-b-nBMA)) of deuterated poly(styrene) CPS(D)) and poly(nbutylmethacrylate) (PnBMA) were investigated by neutron reflectometry with respect to periodicity and interfacial width. Four diffe rent molecular weight P(S(D)-b-nBMA) samples were used to prepare thin film s by spin coating on glass substrates. Two of the samples were in the inter mediate segregated state. The other two samples were in the bulk disordered state, however, due to thin film geometry a surface and substrate induced ordering could be revealed. Utilizing the respective theories (Matsen and B ates for intermediate segregated samples and Fredrickson for a surface and substrate induced ordering), the product of interaction parameter chi and c hain length N was calculated. Taking account for the different molecular we ights, an interaction parameter was obtained which is the same for all of t he four samples, within the experimental error. Using the strong segregatio n theory from Semenov to calculate chi for the intermediate segregated samp les, the interaction parameters for the four samples are not consistent.