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We report on the pressure dependence of the local segmental and normal modes of a type-A polymer (polyisoprene) using dielectric spectroscopy. We find that external pressure exerts a stronger influence on the dynamics of the segmental mode as compared to the longest normal mode which results in the crossing of the two modes at higher pressures. The predictions of the Rouse model are not adequate to explain the different shift factors even at elevated temperatures.

We report on the effect of pressure on the relaxation modes of the type-A polymer polyisoprene as a function of the chain length for M/Me ratio’s (Me is the entanglement molecular weight): 15, 12, 23, 2, and 5. We find that the spectral shape of the segmental and normal modes is invariant under temperature (T) and pressure (P) variations, but the time–pressure superposition fails as a consequence of the stronger P dependence of the segmental mode. The segmental mode activation volume for the different molecular weights was found to scale with the temperature difference from the respective glass transition temperature. Pressure is found to slow down both modes in a quantitatively similar way, irrespective of the chain length, implying that Me is largely independent of pressure.

SummaryMatter-wave microscopy can be dated back to 1932 when Max Knoll and Ernst Ruska published the first image obtained with a beam of focussed electrons. In this paper a new step in the development of matter-wave microscopy is presented. We have created an instrument where a focussed beam of neutral, ground-state atoms (helium) is used to image a sample. We present the first 2D images obtained using this new technique. The imaged sample is a free-standing hexagonal copper grating (with a period of about 36 μm and rod thickness of about 8 μm). The images were obtained in transmission mode by scanning the focussed beam, which had a minimum spot size of about 2.0 μm in diameter (full width at half maximum) across the sample. The smallest focus achieved was 1.9 ± 0.1 μm. The resolution for this experiment was limited by the speed ratio of the atomic beam through the chromatic aberrations of the zone plate that was used to focus. Ultimately the theoretical resolution limit is set by the wavelength of the probing particle. In praxis, the resolution is limited by the source and the focussing optics.

We report on the effect of pressure on the dual segmental relaxation of an athermal poly(isoprene-b-vinylethylene) (PI-PVE) diblock copolymer melt using dielectric spectroscopy. The quantity (∂ log τ/∂P)T is employed as a probe of the state of dynamic miscibility in the system. We find that pressure, unlike temperature, induces dynamic homogeneity.