In-Situ Grazing-Incidence Small-Angle X-ray Scattering of Electrospray Deposited Block Copolymer Thin Films*

Electrospray deposition (ESD) enables the growth of block copolymer (BCP) thin films in a precise and continuous manner by the delivery of sub-micron droplets of dilute polymer solutions to a heated substrate. It also allows the fabrication of uniquely structured films by sequential deposition. We report here the results of in-situ grazing-incidence small-angle X-ray scattering (GISAXS) measurements of BCP thin films during ESD. A custom ESD apparatus was used to obtain synchrotron GISAXS data that provide information regarding the domain spacing and orientation of the developing BCP thin films during film deposition. We examined microstructural evolution during the deposition of a homopolymer, polystyrene (PS), of varying molecular weights onto a lamellae-forming polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) film in the ESD apparatus. The combined thin film exhibited a transition from lamellae to cylinders for low molecular weight PS and loss of structural order above a critical thickness of the deposited PS “top-coat.” We attribute this to volume fraction changes on swelling with PS during ESD. This methodology advanced here enables studies of ordering pathways and the real-time exploration of structure development in thin films fabricated by ESD.