Time: Thursday, April 25th, 2:00 p.m. & Friday, April 26th, 2:00 p.m.
Location: AGGARWAL LECTURE HALL, Room 130
Lectures Are Free And Open To The Public
Polymers are shaped in the fluid state, with typical large flow-induced anisotropy as a result, and used in the solid state, where displacements are limited and properties are determined by the secondary bonds by which chains interact. Modeling the fluid behavior, where temperatures are high and motions are fast, focuses on how chains escape from the affine deformation enforced by the macroscopic flow field, by local chain slip. Modeling in the solid state, where forces are high but motions are slow given the extreme viscosities at these low temperatures, focuses on a quantitative prediction of how the viscosity depends on temperature, stress, pressure, strain rate, and the intrinsic state of the material represented by its age, and by the counter-process that is rejuvenation upon local flow. Ageing kinetics is not only accelerated by temperature, but also by stress itself, since both increase the local segmental mobility. Fluid and solid rheologists surely have to meet when they want to predict the mechanical performance of semi-crystalline polymers. Here the details of segmental orientation of the entangled chains in flow determine not only the orientation and stress during flow, but also nucleate crystallization, enhancing its rate tremendously, but moreover direct the anisotropy of the crystals formed. We are facing a challenge here; fluid and solid rheologists need each other’s theoretical and experimental skills; we are without doubt entering an interesting time of intense cooperation.
For a multitude of high-end applications like for instance polymer photovoltaic’s and polymer membranes for fuel cells and oxygen-nitrogen gas separation, creating large internal surfaces via fractal structuring during polymer processing could result in unique possibilities to enhance performance. Structuring is possible even in processing techniques like in injection moulding provided that two, or more, different plastification units are available that allow sequential and simultaneous injection of multi-materials. Inspired by microfluidic practice, an optimized splitting and recombining static mixer is realized on the parting surface of a mould. Different geometries are used to multiply, rotate and add stratified structures. After the obvious structuring of a huge number of parallel layers, attention is focused on realizing these layers perpendicular to the product’s surface. A combination of the two allows obtaining complex hierarchic fractal structures. A first demonstration of its feasibility is reported.
Han Meijer is full professor in Polymer Technology. He received his Ph.D degree from the University of Twente in 1980 with the late prof. J.F. Ingen Housz as his supervisor. He joined DSM research, and was active in the area of Basic Research, Polymer Processing Modeling and Explorative Research. In 1985 he became part-time professor at the department of Polymer Chemistry and Technology in the area of Applied Rheology. In 1989 he became full professor in Polymer Technology in the group Fundamental Mechanics of the department of Mechanical Engineering. Since then, he built a successful group dealing with dedicated staff that combined modeling and experiments on a 50%-50% basis on basically two topics: (i) structure development in flow and (ii) structure-property relations. In this period, he supervised more than 60 PhD students. Apart from the two main topics of long standing research mentioned, his present interests include: micro-rheology and microfluidics, micro-macromechanics, modeling of polymer processing and design in polymers. And of course America’s Cup sailing.