| dc.description.abstract | Hydrogel is a hydrophilic three-dimension network polymer, which can swell and contain large amount of water within its structure without dissolution. N-isopropyl-acrylamide(NIPAAm) hydrogel has lower critical solution temperature near room temperature. It swells or shrinks below or above the temperature. The dramatic volume change and the low operating temperature characteristics make it a promising mechanism in MEMS devices. To pattern the NIPAAm films, UV photopolymerization is the most common method, which requires the addition of photoinitiators. However, the photo initiators are expensive, difficult to store, and have highly toxic. In this study, we propose a thermal process to prepare and pattern hydrogel thin films, which do not have the disadvantages of the photoinitiator. The thermal process also has the potential fabrication integration in MEMS thermal actuators.
In this thesis, we explore the shrinkage rate, the thermal curing processes, and the local curing of NIPAAm films. In the experiments, the hydrogel solution is coating on a silicon wafer. The wettability tests and optical inspections are used to observe the adhesion phenomenon and the color changes during the heating process at different temperatures. Finally, the micro-heater is used to locally cure the hydrogel film at different environment temperatures to controls the size of the films.
The results show that with the same thickness, the higher the temperature, the faster the hydrogel shrinks; while at the same temperature, the thinner the thickness, the faster the hydrogel shrinks. In the heating process experiments show that the higher the heat temperature is, the faster the hydrogel polymerizes. The activation energy calculated by Arrhenius equation is around 47 kJ/mol. Compared with the wettability tests, optical inspection method can show the curing process with less errors. Finally, the micro-heater experiments demonstrate the feasibility of controlling the curing range of the hydrogel film with a local curing and temperature control of the substrate. | en_US |