Nano-Imaging of Polymers by Optical Microscopy

Conformation of single polymer chain in rubbed thin film observed by fluorescence imaging

The conformation of poly(methyl methacrylate) (PMMA) chains in a thin film after the rubbing process was investigated through the direct observation of the single chains by scanning near-field optical microscopy (SNOM) and excitation polarization modulation microscopy (EPMM). The rubbing at room temperature hardly changed the dimension on the whole chain scale in spite of the increase in orientational order on the segmental scale. The increase in the chain dimension along the rubbing direction was observed in the film rubbed at the higher temperature, which showed a surface morphology with fine groove. The extension ratio of the whole chain in the rubbed film was much smaller than that in the uniaxially stretched film. This indicates that the rubbing process mainly induces the conformational change on the length scale of the monomer unit rather than for the whole chain.

Chain end distribution of block copolymer in two-dimensional microphase-separated structure studied by scanning near-field optical microscopy

The chain end distribution of a block copolymer in a two-dimensional microphase-separated structure was studied by scanning near-field optical microscopy (SNOM). In the monolayer of poly(octadecyl methacrylate)-block-poly(isobutyl methacrylate) (PODMA-b-PiBMA), the free end of the PiBMA subchain was directly observed by SNOM, and the spatial distributions of the whole block and the chain end are examined and compared with the convolution of the point spread function of the microscope and distribution function of the model structures. It was found that the chain end distribution of the block copolymer confined in two dimensions has a peak near the domain center, being concentrated in the narrower region, as compared with three-dimensional systems.

Polysilanes on surfaces

For chain-like polymers on surfaces, the relationship between chain topology and inherent physical properties has long been puzzling due to the lack of proper models and detection systems with ultrahigh sensitivity and high accuracy. Among various chain-like polymers, soluble organopolysilane is one suitable model for elucidating the uniqueness of chain-like polymers on surfaces because of its (1) controllable molecular length, polydispersity, stiffness, and terminal group by an adequate molecular design, a careful synthesis, and a precise purification, and (2) highly luminescent chromophore due to Siσ-Siσ* transition of the Si main chain. This review comprehensively covers the works on (i) molecular imaging with scanning probe microscopy, (ii) tethering on surfaces by a grafting-to approach, (iii) self-assembly, (iv) structural phase transition, (v) orientational phase transition, and (vi) chiroptical switching, memory and amplification in single and double layer films deposited on solid surfaces. This knowledge and understanding may stimulate advanced studies on polymer-based nanoscience, nanotechnology, and nanofabrication as well as in traditional surface chemistry and polymer physics.

Photochemically initiated single polymer immobilization

This Concept article surveys methods for attaching single polymer molecules on solid substrates. A general approach to single polymer immobilization based on the photochemistry of perfluorophenylazides is elaborated.