Numerical and experimental studies in development of polymer injection micro molding.

The present research focused on the investigation of the Injection Micro-Molding process for replication of nano- and micro-patterned polymer surfaces. The major objective of the research was to develop the scientific understanding of the injection micro-molding process both by experimental and numerical studies, and to develop and employ experimental protocols that enable the manufacture of polymer replicated features at the nano- and micro-scale.;This work presents a method for the replication of ordered polymeric arrays from silicon molds treated with plasma polymerized (PP) ultra-thin anti-adhesive organic coating. Silicon molds were fabricated with a-beam lithography and deep reactive ion etching (DRIE) in the BoschRTM process mode. An inductively coupled plasma reactor was utilized to deposit PP coating from C4F 8 (octafluorocyclobutane) precursor gas. Characterization of the PP film was performed via X-ray Photoelectron (XPS) and Fourier Infrared Spectroscopes. Surface analysis revealed excellent chemical composition of the film. Nano-features with different shapes and sizes, as small as 25 nm, were successfully replicated via injection molding with Cyclo Olefin Copolymer (COC) and were imaged with scanning electron and atomic force microscopes. High aspect ratio (AR∼8) submicron-sized pillars were also achieved. Fluorine diffusion from the PP film to the melt processed polymer, detected with XPS as well, decreased with the subsequent molding cycles.;In a different set of experiments, successfully injection molded nano-patterned COC substrates were tested as templates for generation of surface plasmon-polariton excitations. Two very distinct modes of light transmission were observed and their behavior was found to depend on the wavelength influenced scattering from the sub-wavelength-sized pattern.;In addition, experimental protocols were also developed suitable to perform replication of passive optical components, e.g. polymer diffraction gratings, and others which resulted in the manufacture of micron-sized alphanumeric characters.;Static parametric stress-strain structural finite element (FE) analysis revealed that molds made out of Si can keep their structural integrity at the range of pressures and mold temperatures commonly used during polymer injection micro-molding. High principle stresses with values above sigma yield were found to arise only at very high pressures which are unlikely to be used in injection micro-molding applications. Therefore, brittle failure of the Si molds with the considered geometry is not expected to occur during injection micro-molding.;Flow simulations by employing non-elastic Non-Newtonian governing equations describing the behavior of a polymer melt flow under isothermal conditions were considered to simulate the flow in micro-sized cavities as well. In this continuum based FE scheme approach, the expression for the melt viscosity was given with Cross model incorporating Eringen-Okada's term valid for micro-flows. In addition, the flow was considered in the presence of a wall slip. The results were in good agreement with previously reported experimental data. It was shown that the slip velocity introduces a shift in the viscosity vs. shear rate dependence.