Hwa Jin Oh

Precise nanoinjection molding through local film heating system

The temperature control of the mold surface is a key determinant for precision nanoreplication in polymer processing. Here, we introduce a new local film heating system (LFHS) that can precisely control the local mold wall temperature in the nanoinjection molding process. A metal stamp with nanostructures was prepared using micro-electro-mechanical system (MEMS) techniques. We fabricated polymeric nanostructures using LFHS integrated injection molding and carried out modeling on the relevant physical phenomena such as molding and the optical and structural behaviors of the injection molded parts. The findings showed that the application of the LFHS to injection molding led to uniform volumetric shrinkage and high nanopattern quality over the entire part. In addition, the ejection behavior of nanopatterns in the injection molding was modeled to understand the physics of the burr generation.

Photosynthetic solar cell using nanostructured proton exchange membrane for microbial biofilm prevention.

Unwanted biofilm formation has a detrimental effect on bioelectrical energy harvesting in microbial cells. This issue still needs to be solved for higher power and longer durability and could be resolved with the help of nanoengineering in designing and manufacturing. Here, we demonstrate a photosynthetic solar cell (PSC) that contains a nanostructure to prevent the formation of biofilm by micro-organisms. Nanostructures were fabricated using nanoimprint lithography, where a film heater array system was introduced to precisely control the local wall temperature. To understand the heat and mass transfer phenomena behind the manufacturing and energy harvesting processes of PSC, we carried out a numerical simulation and experimental measurements. It revealed that the nanostructures developed on the proton exchange membrane enable PSC to produce enhanced output power due to the retarded microbial attachment on the Nafion membrane. We anticipate that this strategy can provide a pathway where PSC can ensure more renewable, sustainable, and efficient energy harvesting performance.

Surface strengthening of injection molded parts by applying a thermal insulation film

The main objective of this study is to strengthen the surface of injection molded parts by building up the compressive residual stress at the surface of the product. For this, we introduced a mold system for manipulating the heat transfer between the mold and the molten polymer with use of a thermal insulation film. The injection molding process was simulated, and the residual stress was obtained numerically. Experimental analysis of residual stress was also carried out using the hole drilling method. In addition, the scratch resistance and mechanical characteristics of the products were evaluated. The results indicated that the compressive residual stress was built up by employing the film and led to significant enhancement of the scratch resistance and mechanical properties of the molded parts.