Synchrotron X-ray scattering and photon correlation spectroscopy studies on thin film morphology details and structural changes of an amorphous-crystalline brush diblock copolymer

We investigated structural details and temperature-induced structural changes of an amorphouscrystallinebrush diblock copolymer, poly(3-((6-((7-(9H-carbazol-9-yl)heptanoyl)oxy)hexyl)thio)propyl glycidyl ether)60-b-poly(glycidyl 12-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)oxy)-12-oxododecanoate)20 (PGK60-PGF20) in nanoscale thin films using synchrotron grazing incidence X-ray scattering (GIXS) and Xrayphoton correlation spectroscopy (XPCS). Interestingly, the diblock copolymer was found toform a mixture of two different hexagonal cylinder structures (HEX1 and HEX2) where the PGFcylinders were aligned in the film plane. HEX1 was composed of PGF cylinders with higherpopulation of crystals while HEX2 consisted of PGF cylinders with lower population of crystals.Surprisingly, the PGF block chains favorably self-assembled because of strong lateral interactions inthe bristles, forming vertical multibilayer structure with partial interdigitation even in the highlyconfined cylindrical geometry. In heating run up to 340 K, some fraction of HEX2 was transformedto HEX1 via cold crystallization. In contrast, HEX1 was transformed to HEX2 above 340 K becauseof melting of the PGF crystals. The XPCS analysis found that the HEX structural changesassociated with the cold crystallization in the PGF cylinder domains took place with relatively fastdynamics. The HEX structural changes associated with melting of the PGF crystals in the cylinderdomains occurred with relatively slow dynamics; this unusual dynamics of structural changes mightbe attributed to a high energy melting process of PGF crystals against strong lateral interactions ofthe bristles