Effect of the graft chain length and density on the morphology of radiation-modified polysilane monolayers at the air/water interface

The variation in the morphology of monolayers at the air/water interface is investigated for two kinds of radiation-modified polysilanes with different structures: poly(diethyl fumarate)-grafted poly(methyl-n-propylsilane) (PMPrS-g-PDEF) and maleic anhydride-grafted PMPrS (PMPrS-g-MAH). PMPrS-g-PDEF has long but sparsely-attached PDEF graft chains, while PMPrS-g-MAH has short but densely-attached MAH graft units. Surface pressure-area measurements indicate that PMPrS-g-PDEF monolayers extensively spread at the air/water interface though PMPrS homopolymer hardly spreads. AFM observation reveals that PMPrS-g-PDEF monolayers have an inhomogeneous structure containing string-like microstructures. This result suggests that PMPrS main chains are detached from the water surface to aggregate together and only PDEF chains spread over the water surface. In contrast, PMPrS-g-MAH forms uniform monolayers with a smooth surface. PMPrS main chains of PMPrS-g-MAH are anchored to the water surface by densely grafted MAH units. It is also demonstrated that only the PMPrS-g-MAH monolayers are successfully deposited layer-by-layer on a solid substrate by the Y-type deposition.