E. Maurer

Polymeric structures at interfaces: An X-ray scattering study

Abstract X-ray scattering based on synchrotron radiation enables the detection of polymeric structures at interfaces despite the weak contrast between adjacent polymers build-up from different monomeric units. Variable types of polymeric structures result from typical pattern directing mechanisms, such as dewetting in case of homopolymer films, phase separation in polymer blend films, micro-phase separation in diblock copolymer films and surface enrichment in statistical copolymer films. The pattern directing mechanisms introduce structures ordered perpendicular and parallel to the polymeric surface. Consequently, specular and off-specular X-ray scattering is applied as demonstrated within examples. From scattering the characteristic structures which are not accessible by means of other techniques are determined. Limitations with respect to isolated objects such as holes are discussed.

Anharmonic Interactions and the Low-Temperature Thermal Anomalies in Glasses

We study the low-temperature behaviour of an elastic continuum with spatially fluctuating elastic constants and a cubic anharmonic coupling. By functional integral quantization and techniques used previously for treating an electron gas in the presence of disorder and interactions, we obtain an effective action which describes the density fluctuations of the system. By means of a saddle-point approximation we derive a self-consistent set of equations for the density fluctuation propagator Q(ω, T) where w is the frequency and T is the temperature. From the low-frequency solutions of these equations we are able to obtain a mean free path ω -1 Im {Q(ω,T) 1/2 }. This leads roughly to a T 2 law for the thermal conductivity. We also obtain a specific heat which varies linearly with temperature at low temperatures. At higher temperatures the quantity C(T)/T 3 exhibits a peak (boson peak). The former features are due to the anharmonic interactions, whereas the latter is mainly due to the disorder in the harmonic elastic constants.