| Parts with nanoscale features were injection molded to determine the effect of processing conditions and material properties on feature replication. Since the tooling and mold parts were characterized using atomic force microscopy, two measurements, the depth ratio (relative depth the molded features) and the mean surface roughness, were developed to quantify feature replication. While injection velocity and processing pressures had little effect of replication, the melt and mold temperatures affected the ability replicate the nanoscale features from the nickel tooling. Higher melt and mold temperatures usually produced greater depth ratios and smoother part surfaces, thereby linking feature replication to bulk melt viscosity and cooling rates. Unexpected reductions in replication quality suggested that (1) viscosity increases near the mold wall reduced filling rates; (2) melt adhered to the tooling surface when the mold temperature exceeded Tg - 20°C; (3) melt degraded at the tooling surface, and surface energies play an important role in surface roughness of nanoscale replication. Polymethylmethacrylate yielded the best replication and, as expected, semi-crystalline materials were more difficult to handle than amorphous materials. |
