Fr., 21.9.2012, 9:30
Atmospheric pressure plasma for surface modification of polymers in film and fibre form

Abstract:
The generation of surfaces and interfaces allowing control of the interaction with a specific environment, by means of definite surface chemical composition, structure and orientation of particular chemical functionalities, is a major challenge in the development of surface processing techniques. In this respect, plasma represents very reactive environment when in contact with a polymer surface, due to complex contributions from its large variety of energetic species. The physico-chemical reactions break the physical and chemical bonds, yielding active sites, polar groups and scission products onto the polymer surface. Then, depending mainly on the nature of excited species in plasma, plasma triggers the formation of a new functionalized surface layer or a crosslinked surface structure.This work provides a description of various effects of the atmospheric pressure plasma processing on different polymeric materials, in film and fibre form. The plasma parameters and the treatment settings are observed, in relation to relevant surface properties, as surface energy components, surface topography, structural changes and chemical composition. A special attention is given to the contact angle technique, particularly when applied to cylindrical surfaces, with a discussion on methods developed for modeling the shape of drops deposited onto monofilaments.

09.05.2012, 14:00 Uhr
Formulation and Application of a Sparse-Modes Method for Turbulence Simulation

Abstract
Subgrid closure of coarse-grained simulations of turbulent flows is challenging near walls and for multi-physics applications such as reacting flows. The sparse-modes approach can avoid coarse-grained advancement while reducing cost relative to direct numerical simulation. In the formulation described here, the smallest scales of motion are resolved on three arrays of sub-domains, such that each array fills the flow volume and provides full resolution in one coordinate direction. Within each sub-domain, a stochastic model termed One-Dimensional Turbulence (ODT) simulates turbulent flow advancement in the resolved direction. An additional advection process couples the sub-domains so as to capture large-scale 3D motion without requiring advancement of filtered flow properties. This formulation, termed ODTLES, has been used to simulate decaying homogeneous turbulence and various wall-bounded flows. The ability of this sparse-modes type of approach to capture 3D large-scale features while affordably resolving the wall-normal structure of near-wall flow is demonstrated.