Smart (Controllable) Blending and Novel Morphologies Produced by Chaotic Advection

In the Third Millennium, we need to move beyond uncontrollable blending when making plastics, extrusions of various types, and certain high-value added fiber and film products. Currently, polymer blends are formed with little means to obtain desired shapes among components (e.g., of melts A and B) during mixing steps. Blend morphology is for the most part an uncontollable outcome so that extrusions or injection-molded parts are rarely optimized with regard to structure-property relations.  Most often, composition strongly governs morphology. It is preferable to promote and retain specific shapes over wide ranges in composition New directions in the 3rd millennium within polymer melts to effect desired properties.  Fiber glass, for example, would be worthless if the glass fibers were chopped into bits and then added to the matrix component! What if we could blend two or more polymers and deliberately convert them in doing so to multi-layers, platelets, fibers, or other shapes?  We are doing this in the LAPM&T to create plastic products with enhanced properties and also develop processes that are controllable.  Multilayer films have been produced that consist of thousands of individual layers with layer thicknesses in some cases below 200 nanometers.  Fibers have also been extruded that contain thousands of internal fibers.  The multi-layers and internal fibers were formed directly and controllably in multicomponent melts subjected to chaotic advection (also sometimes referred to as chaotic mixing) conditions. Thermoplastic composites have also been produced in this manner with particulate and fiber additives to yield electrically conducting and fiber-reinforced materials. In these materials, percolating structures were in essence constructed in lieu of being the outcome of random associations among additives.

Examples are shown below of some structured polymeric materials and computer-generated results.  In the upper left, a very highly multilayered film morphology is shown. The film layers were formed from polymer melt streams in a continuous chaotic advection blender, also known as a smart blender or chaotic blender, and extruded as filaments.  Similar layered structures have also been extruded in film form. In the color image, conditions to instill 3D chaotic advection throughout a cavity intended for polymer processing were ascertained using pigmented fluids.  Results were cross-checked with computational fluid mechanics models.  In the right upper figure, a computational simulation is shown of a circular blob converted to a folded film (shown in cross-section).  Subsequent modeling and experiments showed that the films multiplied by repeated stretching and folding and fragmented in some cases to yield abundant fibers. For example, very many internal fibers are shown within an extruded filament in the lower left figure.   In the lower center figure, percolating networks were constructed among carbon black particles to render polystyrene electically conducting.  Chaotic advection organized the particle additives into long branched filaments such that interconnections were promoted. In the lower right picture that was generated computationally,  a droplet acted as a type of internal stirrer and improved mixing uniformity by collapsing an island where mixing conditions were poor. While our studies are focused on the development of new polymer processes and materials, fundamentals of general importance to blending and chaotic mixing such as those related to the effects of interfaces among melt components are also addressed.

The demand for products with particular characteristics increases on a daily basis. Manufacturers must meet the specific needs of customers which may change monthly.  Our studies in chaotic advection have demonstrated that shapes among components can be controllably evolved.  Often, for example, large blobs are converted to sheets which refine to multi-layers. Morphological transitions among the layers can lead to many other shapes-many of which may be useful. Notably, many of these morphologies are not observed in common blending equipment since they may only appear locally within devices and as short-lived transitional structures.  In our processes, however, desired shapes can be constructed in situ and delivered to dies for extrusion. Controllable blending methods can make effective use of molecules that are synthesized to have particular processing characteristics and properties.  And of course, with controllable blending technologies, manufacturers can optimize products on-line by also using instrumentation and control technologies. We feel that the time has come to move beyond uncontrollable blending and onward to Smart Blending practices.

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