|Nonlinear Dynamics of Boundary Layers, Heat/Mass
||Fundamentals of Chaotic Advection
||Electrically Conducting Plastics
||Modeling of Multicomponent Chaotic Mixing
|Nano-droplets Formed by Chaotic Mixing
||Novel Interpenetrating Blends & Strength
||Multilayer Blends & Permeation
||Percolating Networks by Chaotic Advection
LAPM&T is the birthplace of polymer blends and composites formed by chaotic advection (chaotic mixing). First studies were conducted with funds provided by the National Science Foundation with work begun in 1991. Thermoplastic blends have been made with novel morphologies such as those consisting of large numbers of layers, interpenetrating phases, fibers, selective or low permeability structures, and very fine droplets even at adverse viscosity ratios. Solid additives also have been placed into functional structures such as percolating networks to render plastics electrically conducting at unusually low additive concentrations. Nanoplatelets have been oriented and selectively placed in thermoplastic matrices to enhance physical properties. The Laboratory has produced the most highly multi-layered extrusions ever made, with individual layer thicknesses less than a few nanometers. Such extrusions can have 10's of thousands of internal layers. Following first fundamental studies, concepts were converted to practical processes and the first patent in this area was awarded with others issuing or pending (e.g., Chaotic Mixing Method and Structured Materials Formed Therefrom, United States Patent Number 6,770,340 B2, August 3, 2004, Inventors: David A. Zumbrunnen and Ojin Kwon).
Due to mixing-based processing, plastic materials which consist of more than one polymer type or include solid additives are not necessarily optimized with regard to structure, properties, and composition. To address these shortcomings, smart blending technology was proposed as a potential non-incremental advance in blending technology. Smart blending devices controllaby develop structure among melt or solid components via intelligent applied agitations. Chaotic advection is enabling to smart blending since melt domains can be stretched and folded in situ. Multilayer melts, while directly useful, are also parent structures to a wide variety of other blend morphologies-all of which can be controllably formed in smart blending devices. Experimental investigations provide a basis for next-generation polymer processing equipment and show how new important materials can be manufactured with much greater versatility. Several new morphologies have been discovered that may be associated with property enhancements. Smart blender/chaotic blender prototypes are the basis for smart blending machines that are commercially available.
In small devices or where fluid viscosity is high, fluids often flow without turbulence. In such cases, it was proposed in 1989 to the National Science Foundation (Grant No. CTS-8918154) that heat and mass transfer can be enhanced by inducing chaotic motions (i.e., chaotic advection) in fluid particles. The chaotic motion would mimic turbulence that is known to improve heating or cooling. (e.g., see "Effect of Flow Pulsations on the Cooling Effectiveness of an Impinging Jet," Journal of Heat Transfer, Vol. 116, pp. 886-895, 1994) Concepts have been adapted by other research laboratories to enhance heating and cooling in micro-channels, micro-electromechanical devices, and electronics.
The vast majority of chaotic mixng studies have considered fluids differing only in color or some other passive identifier. The Laboratory has performed the first studies of chaotic mixing where fluids have different physical properties. Both computational and experimental studies have been performed. These studies show how interfacial effects between fluid components influence chaotic mixing progression. They were primarily done as part of the smart blending research described above, but also have general applicability to chaotic mixing where the focus pertains to mixing and not in situ structure development.
The nonlinear dynamical behavior in unsteady boundary layer flows was
first identified. A boundary layer is a thin region between a flowing fluid
and a physical object where the fluid speed or temperature changes abruptly.
It represents an impedance to transferring heat, for example. In unsteady
flows or where the temperature of the object varies with time, boundary layers
can grow or diminish in thickness. This response is rather like the oscillating
position of a weight attached to a spring, but can be much more complex.
Dynamical boundary layer behavior that occurs in response to flow unsteadiness
was shown to cause either increases or decreases in heat and mass transfer
rates. Results are applicable to gas turbine flows and other flows where
flow unsteadiness occurs, such as pulsating air or water jet flows.
Interestingly, in flows generally, effects often attributed to turbulence
may in some cases actually stem from complex responses in boundary layer
thicknesses to incident flow velocity changes or coherent flow structure-boundary
layer interactions. Results point to new methods for enhancing
or suppressing heating, cooling, or drying rates and also can help distinguish
effects caused by unsteadiness from those caused by turbulence.
The principles of materials science and transport phenomena (e.g., diffusion, complex liquids) are applied in the Laboratory for Advanced Plastic Materials & Technology in research to develop advanced plastic materials and processes. Investigations are performed to further fundamental understanding while also directly benefiting industries and governmental agencies. Polymer blending, polymer films and fibers, polymer composites, injection molding, physical property characterization, computational modeling of non-Newtonian flows in multi-component melts, applications of chaotic advection and chaotic mixing, and heat/mass transfer are subjects under investigation.