UCLA

Smart windows with tunable optical transmittance to electrical-, thermal-, mechanical stimuli offer promising solutions for energy saving application in the field of novel building, vehicles, agriculture, etc. Among which, the thermal responsive smart window arouses great interest due to its passive response, without introducing external energy. Numerous studies have been conducted, yet several critical challenges remain unresolved, including undesired transition temperature, slow transition in temperature span, low transparency at clear state, and limited optical modulation capability.

The phase changing polymer shows extraordinary thermal responsive optical switching capability base on melting and crystallization. By introducing another distinguishable phase into the established phase changing polymer network to create refractive index matching and mismatching, the optical modulation is achieved at different temperature stage.

I developed a series of thermal responsive smart window materials based on side chain crystallizable phase changing polymer, to accomplish smart windows with tunable transition temperature ranging from 32 °C to 45 °C, ultra-high low-temperature visible transmittance above 91%, and excellent optical modulation capability higher than 80%.

Chapter 1 outlined the background of the imperative for smart window of modulating solar radiation, for energy conservation purposes.

In Chapter 2, I introduced a thermal responsive phase changing polymer (TPCC), which was synthesized from hydrophilic and hydrophobic monomer blends. The phase transition of the semicrystalline polymer led to a refractive index drop, effectuating light scattering and facilitating optical modulation across the solar spectrum. The transition temperature for this smart window was designed to be 32 °C.

In Chapter 3, I presented a semicrystalline polymer with exceptional transparency between 20 °C to 60 °C. By employing such polymer as the functional thermal responsive material, a high transmitted state of the smart window was achieved, with transmittance varying from 91.4% at 20 °C to 2.7% at 50 °C. The transition temperature for this smart window design was around 42 °C.

In Chapter 4, based on the previous transparent semicrystalline polymer, I enhanced the smart window performance by introducing glass beads to realize a controllable light scattering. A high contrast in optical transmittance between 96.8% and 3.2% was achieved, signifying its capability of optical tuning.

These materials demonstrated the viability of using such semicrystalline polymers for smart window applications to address a high capability of optical modulation >80% with a more desirable transition temperature between 32 °C and 45 °C. A total low-temperature transparency and wavelength selected modulation could be further achieved by material selection and refractive index tuning cooperate with the established materials.