Understanding Segregation Processes in Blends of Bottlebrush-Linear Polymer Thin Films

Bottlebrush polymer thin films have potential to generate surface coatings for a variety of applications ranging from tailored surface wettability and adhesion, antifouling surface coatings and self-assembled photonics. In this study, we examined the phase behavior for athermal blends of bottlebrush polystyrene (PS) and linear deuterated polystyrene (dPS) in thin films. The bottlebrush loading was 10\% by volume, and the ratio of linear dPS chain length to bottlebrush PS side chain length was systematically varied in the range of $\alpha = 0.3-41$. The depth-dependent concentration of bottlebrush was measured using dynamic secondary ion mass spectroscopy. When $\alpha < 2$, the bottlebrushes are dispersed throughout the film thickness with a slight excess at the free surface and substrate interface. When $\alpha > 8$, the bottlebrushes are depleted from the interior of the film and segregated at the interfaces. This behavior is consistent with wetting and dewetting transitions at a melt/brush interface and entropic attraction of highly branched polymers to surfaces. This work demonstrates that brushlike surfaces and interfaces can be generated in a linear polymer film through spontaneous, entropy driven segregation of properly designed bottlebrush additives.