This work demonstrated, developed and characterized a new and novel technique for plastics welding using diffractive optics. Using diffractive elements laser beams were reshaped into various geometries that could be used for simultaneous welding of plastic in through transmission infrared welding. This novel technique also included the use of standard optics for resizing diffractive images for microwelding of complex geometries. In addition, new molecular healing models that accurately predict weld size and quality (degree of healing) were developed. The ability to quickly and economically form microwelds is critical to the development and commercialization of polymer-based MEMS and micro-fluidic devices.; Thermoplastics offer significant advantages in the fields of biomedical engineering, communications, and in particular applications related to Micro Electro Mechanical Systems (MEMS). For example, the low manufacturing costs of polymers may allow industry to fabricate disposable MEMS. Rapid, consistent, and inexpensive assembly or packaging is critical to the commercialization of polymer-based MEMS. One method of joining that offers great promise of success for MEMS devices is Through Transmission Infrared (TTIr) welding. TTIr works by passing a laser through one of the components to be joined and focusing it on the second, which has an absorbing material (such as carbon black) added to it. In the following studies, diffractive optics were used to reshape a laser beam into complex shapes for TTIr welding of plastics. These complex image shapes were then resized to micron-scale for micro-welding of plastics.; Another task of this work was to gain a better understanding of molecular healing so that micro-welds could be better understood. Because minimum weld size is affected by competing driving forces, namely thermal conductivity and molecular diffusion, these forces were studied. For example, as time increases heat conduction results in an increase in weld size, thus minimum heating time is desired to produce small welds. In contrast, molecular healing is also proportional to time, thus increasing the heating time increases weld strength. In addition, these two mechanisms are limited by maximum allowable temperatures, where the base material can degrade or ablate. Thus, increasing the temperatures (power) is also limited. (Abstract shortened by UMI.)
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