Dynamic secondary ion mass spectrometry was used to investigate the chain mobility of polystyrene (MW ranging from 4.3 to 957 kg/mol) at the free surface. The data show that the diffusion coefficient was reduced relative to the bulk value within a distance, d < or = 4R(g), from the surface and scaled as 1/N(2.5) at fixed d. These results are in excellent agreement with self-consistent field calculations of the surface segmental distribution and provide the first direct confirmation of various theoretical models that predict asymmetric segmental fluctuation which arises from surface induced orientation of polymer chains.

Thin poly(styrene210-b-2-vinylpyridine200) and poly(2-vinylpyridine94-b-styrene760-b-2-vinylpyridine94) films spun cast on silicon and annealed at 180°C for 3days were directly cross sectioned in less than 1h using the focused ion beam (FIB) lift-out technique. We show that with the FIB procedure, it is possible to produce cross sections that reveal structure near the silicon interface and hence the surface induced phase transitions could be examined and compared quantitatively with theoretical models. Atomic force microscopy, dynamic secondary ion mass spectrometry, and transmission electron microscopy were used to characterize the films.

With the increasing importance of thin film in various applications, there is a need for new techniques with high surface sensitivity to measure physical properties. In this paper, we report results using a recently developed technique based on atomic force microscopy, temperature-dependent shear modulation force microscopy (SMFM), to investigate the surface glass transition. We test the effects of pressure under the tip, modulation frequency, and driving amplitude, which have been the subject of some controversy. The glass transition measurements on polystyrene and poly(methyl methacrylate) with different sample geometries demonstrate that the active volume probed by this technique has lateral dimensions on the order of the tip-sample contact radius. Applications to thin film glass transition measurements and surface segregation in long-chain/short-chain blends demonstrate the general utility of this technique.

Dynamic secondary ion mass spectrometry was performed to determine the dynamics of thin free-standing polystyrene films by investigating probe diffusion in a high molecular weight polymer matrix. It is found that the temperature dependence of the diffusion of small molecular probes can be described by the WLF equation above bulk T-g, whereas a weaker dependence is found below T-g for PS films with total thickness as thin as 69 nm. The results of probe diffusion as a function of film thicknesses show no change of T-g for the free-standing films with thickness ranging from 33 to 200 nm.

We have measured the tracer diffusion coefficient in PS films oriented by surface rubbing. The results show that the diffusion perpendicular to the rubbed surface is slower in oriented than in nonoriented chains. The decrease of the diffusion coefficient was correlated with the total oriented volume as determined by birefringence measurements.

We have performed X-ray specular and off-specular measurements of free-standing polystyrene thin films as a function of molecular weight and thickness. The results show films thicker than a few radii of gyration (R-g) are well fit by a simple liquid model. This confirms the assumption that the anomalies previously reported in the scattering intensity from polymer films of comparable thickness were mostly due to confinement by long-ranged interactions with the substrate rather than a fundamental property of viscoelastic fluids. The simple liquid model was found to be insufficient to fit the transverse diffuse data for films thinner than a few R-g. Longitudinal diffuse scattering data demonstrated that the roughness at the two interfaces is highly correlated when the film thicknesses are approximately 2R(g). Hence, very thin films do not exhibit liquidlike behavior, and higher-order elastic terms may have to be included into models to describe their rheological behavior.

We report results of glass transition (T(g)) measurements for polymer thin films using atomic force microscopy (AFM). The AFM mode, shear modulation force microscopy (SMFM), involves measuring the temperature-dependent shear force on a tip modulated parallel to the sample surface. Using this method we have measured the surface T(g) of thin (17-500 nm) polymer films and found that T(g) is independent of film thickness (t>17 nm), strength of substrate interactions, or even presence of substrate.