Polymeric microstructures and microchannels are widely used in biomedical devices, optics, microfluidics and fiber optics. The quality, the shape, the spacing and the curvature of microstructure gratings are influenced by different mechanisms and fabrication techniques used. This paper demonstrates a cost-effective way for patterning high-aspect-ratio thermoplastic microstructures using thermal imprint technology and finite element modeling. Polymeric materials polypropylene (PP), polyethylene terephthalate glycol (PETG), polyvinyl chloride (PVC) and styrene-acrylonitrile (SAN) were chosen for the experimental investigations. A finite element model was constructed to define the most suitable parameters (time, heating temperature, pressure, etc.) for the formation of microstructures using the thermal imprint procedure. To confirm the relevance of the finite element model, different types of PP, PETG, PVC and SAN microstructures were fabricated using theoretically defined parameters. Experimental investigations of imprinted microstructures’ morphological and optical properties were performed using scanning electron microscopy, atomic force microscopy and a diffractometer. Obtained results confirmed the relevance of the created finite element model which was applied in the formation of high-aspect-ratio microstructures. Application of this model in thermal imprint would not only reduce the fabrication time, but also would highly increase the surface quality and optical properties of the formed structures.
In recent days, microgeometry is being widely used in medicine, microchip technologies, mechatronic systems, or innovative sensors [1][2][3]. Microgeometry can be formed by various methods depending on the desired structure. Polymeric materials are distinguished by the possibility of forming structures using a hot embossing method. This method can ensure a high-quality structure and a high speed of its formation [4]. However, it is difficult to ensure the necessary parameters for different geometries in the experiments. Therefore, computerized finite elements are used for this purpose [5].Using ANSYS software, a model was created that can be used to predict the necessary parameters for the formation of the microstructure. Since a main matrix structure was experimentally produced using reactive ion etching technology, which achieved a 4 μm periodicity and a groove depth of 1 µm of microstructure, the corresponding model of the matrix structure was created in theoretical calculations. The characteristics of the material (strain, stress, and Young's modulus) were additionally described to change the mechanical characteristics when the temperature changes. Due to the relatively large deformations, a non-linear adaptive domain was used for mesh recalculation. In addition, the model was simplified using fixed and frictionless supports. An animation of strain, elastic strain, stress, and reaction force graph were generated. After performing theoretical calculations, the obtained results allowed to see how the plastic flows into the mold. It was observed that at lower temperatures, the plastic mold was not filled. During the experiment, the reaction force was obtained, which made it possible to select the optimal pressure force at a specific temperature.The theoretical model described in this article allows to predict the geometry of the formed structure and the necessary parameters to form the microstructure. Moreover, the model can show invisible defects such as residual stresses. In addition, for more complex casting geometry, the model can be adapted to find the optimal parameters.
Molding in thermoplastic polymers using ultrasonic hot embossing technology is promising due to its high precision reproducibility. To understand, analyze and apply the formation of polymer microstructures by the ultrasonic hot embossing method, it is necessary to understand dynamic loading conditions. The Standard Linear Solid model (SLS) is a method that allows analyzing the viscoelastic properties of materials by representing them as a combination of springs and dashpots. However, this model is general, and it is challenging to represent a viscoelastic material with multiple relaxations. Therefore, this article aims to use the data obtained from dynamic mechanical analysis for extrapolation in a wide range of cyclic deformations and to use the obtained data in microstructure formation simulations. The formation was replicated using a novel magnetostrictor design that sets a specific temperature and vibration frequency. The changes were analyzed on a diffractometer. After the diffraction efficiency measurement, it was found that the highest quality structures were formed at a temperature of 68 °C, a frequency of 10 kHz, a frequency amplitude of 1.5 µm and a force of 1 kN force. Moreover, the structures could be molded on any thickness of plastic.
In this paper, synthesis of nanocomposite and experimental investigation of three samples of nanocomposite films are presented. The aim of this research is to determine influence of the PZT particle concentration in nanocomposite on the surface morphology, qualitative and quantitative chemical composition ant direct piezoelectric effect. The specimens were prepared by mixing the PZT nanopowder with PMMA in three different proportions: 85% of PZT and 15% of binder; 90% of PZT and 10% of binder; 95% of PZT and 5% of binder. Surface morphology and qualitative and quantitative chemical composition were evaluated using scanning electron microscope, which is equipped with the Energy Dispersive X-Ray Spectrometer. Electrical response of the pulse-excited specimens is also presented.
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