| dc.description.abstract | Icing is one of the most ubiquitous natural phenomena accompanying human activities. Undesired ice generation and accretion are extremely hazardous to aircrafts, ships, electrical transmission cables, wind turbines, motor vehicles and many others. Combating excessive icing, especially active de-icing, has been costing a huge amount of energy and time annually global-wide. Consequently, designing and deploying material surfaces that can assist the removal of ice have received growing interests. In the recent years, it is witnessed that anti-icing strategies are shifting from being of static nature, namely no change at the ice-substrate contact area after ice formation, to enabling dynamic changes in the chemical/physical states of the ice/substrate/ice-substrateinterface with tailored functions. In contrast to the static anti-icing surfaces with known deficiencies in icing/deicing cycling durability, inapplicability at extremely low temperature, fragility to surface damage and surface degradation, and inadaptability to environment changes, the modern dynamic anti-icing surfaces (DAIS) have intrinsic superiorities in all respects of materials properties and enhanced anti-icing performances, thanks to their integrated dynamic functions. It is expected that a new variety of DAIS will be created in the near future as they are attracting tremendous interests in the research field.
By definition, DAIS are surfaces that possess spontaneous/stimuli-responsible changes of the chemical/physical state of the substrate, ice, or the ice-substrate interface. The currently reported DAIS can be classified into three categories depending on where the dynamic change takes place, namely surfaces with dynamic substrate change, with dynamic interface change, and with dynamic ice change. Built upon the understanding of dynamic anti-icing surfaces, novel anti-icing surfaces can be designed by integrating dynamic behaviors into substrate, ice-substrate interfaces or ice.
Focusing on dynamic substrate change, thermal responsible surfaces that can dynamically change the phase of lubricant with decreasing temperature for enabling durable icephobicity are designed. Generally, maintaining the longevity and durability of slippery liquid infused porous surface (SLIPS) are of great challenge. A novel phase transformable slippery liquid infused porous surface (PTSLIPS) is invented to overcome the formidable barrier. The underlying mechanism of PTSLIPS relies on the physical property of lubricant that enables transformation from liquid to solid state above water freezing point. Specifically, peanut oil is chosen to infuse into porous PDMS substrates for creating PTSLIPS, which show low ice adhesion strength (4 ∼ 22 kPa) as well as excellent durability. For selected samples, the low ice adhesion strength (∼ 16 kPa) maintains after 30 icing/de-icing cycles thanks to the solid state of the lubricant, demonstrating extraordinary long-term icephobicity. In addition to the promising low ice adhesion strength and durability, PTSLIPS also suit to various substrates of varied chemical compositions (both hydrophobic and hydrophilic materials) with wide range of porosity and diverse pore morphologies. The PTSLIPS, therefore, provide the possibility of creating anti-icing surfaces by Do-It-Yourself (DIY) manner with porous materials in daily life.
Turning to dynamic change of the icing interface after ice formation to facilitate easy ice removal, liquid layer generators (LLGs) are designed for the first time. The LLGs can release ethanol to and constantly change the ice-substrate interface. As predicted by atomistic modelling and molecular dynamic simulations, interfacial ethanol layers with different thickness can provide dramatic reduction in ice adhesion even at extremely low temperatures. Two types of LLGs, namely LLG 1 by packing ethanol inside substrate and LLG 2 by storing replenishable ethanol below substrate, are fabricated. The interfacial ethanol on both the two LLGs converts the ice-substrate contact from the solid-solid mode to the solid-liquid-solid mode, which results in super low ice adhesion around 1.0 kPa at -18 °C. Attributing to the constant ethanol release and thickening of the interfacial lubricating layer, LLG can overcome the deficiency induced by surface roughness and hydrophilicity, the two well-known critical factors that result in the failure of other icephobic surfaces. The LLG 1 have a lifespan for a maximum of 593 days without ethanol source replenishment. By introducing an interfacial ethanol layer, ice adhesion strength on selected samples with rough surfaces decrease in an unprecedented manner from 709.2 ~ 760.9 to 22.1 ~ 25.2 kPa at a low temperature of -60 °C. The results validate the LLGs as competitive candidates for practical anti-icing applications and provide an unprecedented icephobic solution for extremely low temperatures.
In a summary, by overcoming the limitations of the static nature of the current antiicing surfaces and focusing on the dynamic properties, novel anti-icing strategies are explored, varying from the dynamic substrate changes to the dynamic interface changes. Based on the different dynamic design principles, two anti-icing surfaces, the phase transformable slippery liquid infused porous surfaces, PTSLIPS, and the liquid layer generators, LLGs, are developed in this PhD work, both of which demonstrate excellent anti-icing performances.
Taking a bird-view on the DAIS, the related state-of-the-art research is also covered in the last appended paper. With the two fabricated surfaces as illustration and the surveyed development of the research, this thesis is intended to serve not only as the PhD concluding milestone but also as helpful reading materials for researchers in the anti-icing field. | |
