Conformation of Single Poly(methyl methacrylate) Chains in an Ultra-Thin Film Studied by Scanning Near-Field Optical Microscopy

The conformation of a single poly(methyl methacrylate) (PMMA) chain was studied by scanning near-field optical microscopy (SNOM). Here we discuss the conformation of PMMA in the confined geometry of the thin film with a thickness less than the unperturbed chain dimension in the bulk state. The direct observation by SNOM was performed for individual fluorescence-labeled PMMA chains dispersed in the thin films of the unlabeled PMMA prepared by the spin coating and Langmuir-Blodgett techniques. We examined the effect of the constraint in the height direction on the radius of gyration in the direction parallel to the film surface, Rxy, i.e., the chain dimension normal to the confinement. In the thickness range of 1–100 nm, Rxy in an ultra-thin film was not significantly altered from that in the bulk state, indicating that the PMMA chain has lowered interchain entanglement in the ultra-thin film.