Band 9, Heft 1

Foams have been prepared from water added with a surfactant (Sodium-Dodecyl-Sulfate, SDS) and a polymer (Poly-Ethylene-Oxide, PEO) at different concentrations. This work was devoted to a study of the flow properties of the foams. The pressure drops were measured during flow in capillary tubes (2.5, 3.5 and 4 mm) in laminar regime. It was found a strong dependence of the flow curves on capillary diameter showing that pronounced wall slip effects exist. Two known approaches were applied to quantify the slip velocity: (a) the Mooney method, in which the key assumption is that the slip velocity depends only on the wall shear stress, was not applicable and (b) the Oldroyd-Jastrzebski method, in which the assumption is that the slip velocity depends not only on the wall shear stress but also on the flow geometry, yielded satisfactory results. The determination of the pressure drop coefficient showed that the Metzner and Reed correlation, i.e ., the Reynolds analogy based on the generalised Reynolds number, could be applied if the data are corrected for slip effects.

GENERIC is reviewed not only as a new general framework for modeling nonequilibrium systems, but also as a new way of thinking about nonequilibrium dynamics. This unified framework of nonequilibrium thermodynamics is shown to be deeply rooted in the ample accumulated experience with nonequilibrium systems and, provided that state variables with slow and fast time-evolution can be separated, the framework can actually be derived. In view of its natural capability of modeling systems on different levels of description, GENERIC is ideal for the highly topical attempts of “bridging scales” in science and engineering. The practical usefulness of GENERIC as a powerful tool in the phenomenological and structure-guided modeling of complex fluids is illustrated through two examples.

The design of an instrument capable of opto-mechanical studies of the rheology of viscoelastic polymeric fluids near solid interfaces is described. The instrument probes the ‘meso’-scale (length scales of 0 (μm)) and bridges the gap between molecular-scale devices such as the Surface Force Apparatus (SFA) and conventional rheometers. The high viscosity materials and intermediate length scales probed with the current device are of direct relevance to industrial coating and thin film polymer processing operations, in addition to fundamental investigations of slip and interfacial instabilities. The device utilises small fluid samples (of the order of 1 μL), allows a wide range of viscosities (and thus molecular weights) to be investigated and can also be used with different substrate materials and surface coatings. Direct optical access to the sample also permits in-situ rheo-optical studies of material response under different loading conditions and flow histories.