Effects of Relative Humidity and Nanoparticle Incorporation on Nanostructures of PS-b-PEO Diblock Copolymer

摘要

This paper is comprised of two major sections: (1) effects of relative humidity (RH) on nanostructures of polystyrene-block-poly (ethylene oxide) (PS-b-PEO) diblock copolymer, and (2) the structures of PS-b-PEO after incorporation of nanoparticles. Thin films of PS-b-PEO were prepared by spin coating under different RHs. Effects of RH on the nanostructures of self-assembled PS-b-PEO were investigated using atomic force microscopy (AFM). The stability of the formed structures under different RHs at ambient temperature was studied in-situ by AFM with the aid of a small volume AFM environmental chamber. The results show that the orientation and the ordering of the copolymer nanostructures are very sensitive to the humidity of the environments during film formation. Well-defined cylindrical nanodomains oriented perpendicular to the surface are induced by the high humidity during spin coating. These perpendicular cylindrical structures are stable at different levels of RHs, except that at very high RH (90 %), the PEO domains are swollen to form mushroom-like structures. Upon drying, the original nanostructures of the copolymer re-form, indicating that these structural changes are reversible. Moreover, the AFM phase contrast between the cylindrical PEO domains and the PS matrix is significantly increased at the elevated RHs. To prepare inorganic-organic nanocomposites, the sol-gel precursor of titinia was introduced to the PS-b-PEO system. The overall morphological structure of the PS-b-PEO is altered after nanoparticle incorporation. The cylindrical nanodomains are still observed, but are not as well-defined as those in the pure PS-b-PEO system. For the materials and the conditions studied, the aggregation of the nanoparticles appears to interrupt the long-range ordering of the copolymer nanostructure.