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, R-xy, i.e., the chain dimension normal to the confinement. In the thickness range of 1-100 nm, R-xy 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.