Julie Chen, Mechanical Engineering; Hongwei Sun, Mechanical Engineering; Carol Barry, Plastics Engineering; David Kazmer, Plastics Engineering
In the current quest to establish new technologies for high-rate nano-scale manufacturing of polymers, the link between processing experiments and process modeling relies on the correct representation of the material behavior at these scales. As the geometric dimensions of tooling features shrink down to the nano-scale, the polymer behavior is in the intermediate regime between continuum and molecular dynamics dominated conditions. The number of molecules at this scale is high enough to make molecular dynamics models too computationally expensive, but too low to make continuum assumptions about averaged bulk behavior, neglecting interface and surface effects. At the nano-scale, the typical Reynolds number is much less than one due to the small transverse length scale, which results in a high velocity gradient and thus high viscous forces. Furthermore, due to the large surface to volume ratio, these macromolecular polymers are not very far from the tool surface and the motions are influenced by the surface potential, which leads to a poorly-understood region of interfacial effects. Some of the questions that arise are how does the polymer-tool interaction change (i.e., slip, stiction); what is the viscosity; and how can the material behavior be measured? In an attempt to answer these questions, efforts need to be made to identify the significant factors that influence the nano-scale (500µm – 10nm) polymer flow behavior and to develop an experimental setup to quantify these behaviors.
The following research, in coordination with ongoing research in the Center for High-rate Nanomanufacturing in modeling and micro-injection molding of nanofeatures, will thus focus on developing an experimental setup for flowing polymeric fluids through well-defined micron and nano sized channels to mimic actual operating condition, conducting tests with different fluids and different flow rates in channels having dimension range of 1mm to 1µm and comparing experiment results with simulated results to inform further improvements of simulations and tooling design.