Stimuli-reponsive polymer composite for energy saving thermotropic smart window
Lee, Heng Yeong
Date of Issue2018-08-13
School of Materials Science and Engineering
Transparent glasses are hotly pursued as premium construction materials in transport vehicles and architectural buildings for its aesthetic appeal. Due to widespread usage of transparent glasses, 43% of global world primary energy are spent on heating, ventilation and air-conditioning in buildings. Moreover, individual can also experience uncomfortable situations, such as glaring sunlight, skin and thermal discomfort. Current practice of using multi-layered optical solar films for solar shielding requires costly fabrication process and further results in low visibility and disruption of communication signals. Although solar modulation system driven by external stimuli have been demonstrated, these systems usually involve costly installation, complex device fabrication process and rely on external mechanical or electrical stimuli. Hence, an autonomous system driven by solar heating itself to exhibit broadband solar modulation would be ideal. The closest class of material that could perform in such manner is the thermally responsive hydrogel, a material containing around 90% of water. Unfortunately, their chances of commercialization are largely detracted by their inherent shrinking and aqueous characteristics. In this thesis, a new class of phase transition material that can respond to temperature change was developed. With the increase in temperature, different degree of reversible solar modulation can be achieved and tailored accordingly to a wide range of operating temperatures. The components in this new material consists of ionic liquids which are intrinsically stable and polyurethane elastomer which is not only cost effective, but further endow the material with mechanical robustness. The distinct advantages of broad transition range tunability, cyclic stability and functional versatility in the material system is unattainable by any existing solar modulation solution. This is the first time where ionic liquids were explored as material for thermotropic smart window and the resulting new material super cyclic stability with critical non-volatile and non-freezing properties can be attributed to the superior intrinsic characteristics of ionic liquids. This new material also allows facile and unparalleled tuning range of transition temperature (tuning via multiple parameters). The mechanism of the underlying thermally responsive interactions in this new class of material was extensively elucidated and applied in smart window application for the very first time. In a parallel study, plasmonic particles which exclusively absorb in near infrared region was coupled with thermally responsive hydrogel. Experimental results show that both the response speed and solar modulation of the thermotropic composite could be enhanced. Photothermal characteristics endowed by the plasmonic particle not only enhance the thermal insulation features for tropical climates but further enable optical switching in cold weather climates. The mechanism of plasmonic heating coupled with thermally responsive polymer for smart window was reported for the very first time. Combination of the above novel technologies offers a unique competitive advantage and result in a new class of thermally responsive organic/inorganic hybrid which can be affixed as an interlayer laminate for a fully autonomous smart window to achieve energy conservation. Apart from their application in transport vehicles and architectural buildings, this new material may also find itself in other numerous optical applications, such as over-heating protector for solar panels and other smart devices with memory or sensing functions. It is believed that the novel outcomes from this research thesis will fit neatly into the technological gap concerning green and smart buildings. It will also be propelled by the rapid development and pressing demand of innovative solutions in a highly competitive automotive industry.