The local conformation of polymer chains in a film at a substrate interface was examined by sum-frequency generation spectroscopy. When a polystyrene (PS) film was prepared on a quartz substrate by a spin-coating method, the chains were aligned in the interfacial plane of the substrate. A dissipative particle dynamics simulation revealed that a spinning torque induced the chain orientation during the film preparation process and the extent of the orientation was a function of the distance from the interface. This interfacial orientation of chains was not observed for a PS film prepared by a solvent-casting method. Interestingly, the local conformation of chains at the substrate interface was unchanged even at a temperature that was 80 K higher than the bulk glass transition temperature (T g). This observation means that polymer chains at the substrate interface can be only partially relaxed under conditions where the bulk chains are fully relaxed. On the other hand, interfacial chains could be easily relaxed by solvent annealing.

The local conformation of poly(methyl methacrylate) (PMMA) chains at the nitrogen (N 2 ) and water interfaces was studied by infrared-visible sum-frequency generation (SFG) spectroscopy. Although SFG spectra in the C-H region for PMMA at the N 2 interface have been hitherto reported, the peak assignments are not in accord with one another. Thus, we first made accurate assignments of SFG peaks using films, which had been well annealed at a temperature above the glass transition temperature for a long time, of three different deuterated PMMAs as well as normal protonated PMMA. At the N 2 interface, hydrophobic functional groups such as a methyl, ester methyl and methylene groups were present. While the a methyl group was oriented along the direction parallel to the interface, ester methyl and methylene groups were oriented normal to the interface. Quantitative discussion concerning the orientation of the functional groups of PMMA at the N 2 interface was aided by a model calculation.Once the PMMA film contacted water, the carbonyl groups of the PMMA side chains were oriented to the water phase to form hydrogen bonds with water molecules, resulting in the migration of ester methyl into the internal region of the film. Concurrently, the methylene groups became randomly oriented at the water interface and/or in part migrated into the internal region. Interestingly, the a methyl groups still existed at the water interface oriented along the parallel direction. The outermost region of PMMA in water can consist of hydrophilic and hydrophobic domains with sub-nanometre scale. Water molecules H-bond to themselves near the hydrophobic domains, leading to the formation of an ice-like structure of water molecules. However, water molecules adjacent to the hydrophilic domains H-bond with carbonyl groups.

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