Experimental study of phase transitions in mixed polymer brush melts on planar substrates has largely lagged behind in validating the phase behavior predicted by theory and simulation. This is due to experimental limitations in meeting the assumptions that go into these predictions such as high grafting density, uniformly, and predictable chain length. We have designed a single component copolymer based cross-linked coating to grow mixed polymer brushes with excellent control over homogeneity of grafting sites, dispersity, chemical functionalities, ability to grow low to high molecular weights, and with stability to thermal annealing conditions. Specifically, we focus on poly(methyl methacrylate) (A)/ polystyrene (B) (PMMA/PS) mixed brushes with equal number of A/B chains (see attached figure). Our studies show that even with equal grafting density of the A and B the morphology can be modulated by varying the length of B chains while keeping that of A fixed. We show the very first example of transition of self-assembled structures from disorder to cylinder to ripple phase at a sub-30 nm length scale on a planar surface. These results are supported by a new phase diagram established through Monte-Carlo simulation using a coarse-grained particle-based model.

Phase behavior of mixed polymer brushes grown from ultra-thin coatings

2019 Fall National Meeting

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