Precision synthesis and neutron reflectivity experiments coupled with self-consistent field theory (SCFT) can provide unparalleled insights into the physics of polymers near interfaces. In this work, we studied the effects of polydispersity on the microphase separation lamellar forming di-block copolymer thin films. A dually reactive block copolymer containing a polydisperse block of poly(glycidylmethacrylate) (PGMA) connected to a near-monodisperse block of poly(4,4-dimethyl-d6-2-vinylazlactone) (PVDMAd6), PGMA142-b-PVDMAd6148, was synthesized. SCFT predicted that the symmetric di-block copolymer has a lamellar morphology in the bulk. The morphology was confirmed by transmission electron microscopy (TEM) and small angle neutron scattering (SANS) experiments. In order to study the microphase separation in thin films, dilute solutions of the block copolymer were deposited onto silicon substrates and annealed above the polymer’s glass transition temperature resulting in films with thicknesses of 12.3 nm, 28.6 nm, and 41.2 nm. Specular neutron reflectivity experiments were done to probe the number of strata in the films along with the spatial distribution of each block. SCFT was used to predict the structure of the thin films and to construct the models used to fit the neutron reflectivity data. A relatively good agreement between the experimental and theoretical results was observed providing useful physical insights into the thin film structure of PGMA142-b-PVDMAd6148. In particular, it was found that the polydispersity causes entropic segregation resulting in the polydisperse block (i.e., PGMA) residing in the middle of the film despite favorable interactions with the silicon substrate. The entropic effects were found to be the driving force for assembly in ultra-thin films with thicknesses of 4-5 times the radius of gyration. Furthermore, the coordinated experimental and theoretical study has led to the development of a facile and robust framework that can easily be tailored to study other polymeric systems near interfaces.

Coordinated experimental and theoretical study of a polydisperse polymer thin film

249th National Meeting (2015)

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