Wu, Mengjuan
(2023)
Study on multi-phase structured icephobic constructions.
PhD thesis, University of Nottingham.
Abstract
The accumulation of ice on critical infrastructure, such as aviation, telecommunication, electricity, and transportation systems, can cause severe disruptions to daily life and significant economic losses. While applying icephobic coatings has been proposed as a potential solution, the challenge remains in creating coatings that can effectively withstand adverse environmental conditions, and also demonstrate a long service life and mechanical durability. The motivation of the work is to provide a comprehensive analysis of the fundamental aspects related to icephobicity research, and to explore novel, durable icephobic materials and surfaces, to produce well-rounded research outcomes.
Liquid-infused surfaces (LIS) with self-replenishing properties have been adopted for anti-icing and de-icing applications. However, the mechanical durability of the LIS polymer is limited, rendering them unsuitable for long-term practical use in ice protection. To alleviate the difficulties associated with limited mechanical durability and rapid oil depletion among LIS structures, this study proposes a multi-phase LIS construction based on microporous metallic scaffolds. The proposed approach aims to tackle the problem of icephobicity deterioration in LIS materials. Specifically, the study employed Ni scaffolds and a PDMS-modified silicone oil (NP-SO) system for the LIS construction. The inclusion of Ni scaffolds facilitated stress redistribution during de-icing, thereby safeguarding the LIS material from external loads and impacts. As a result, the ice adhesion strength of the NP-SO samples down to 2.0 ± 0.7 kPa after undergoing 50 cycles of anti-icing/de-icing tests. Conversely, samples without Ni scaffolds demonstrated surface damage after 30 cycles of anti-icing/de-icing tests. The rapid depletion of infused oil due to large polymer deformation was also addressed. The multi-phase construction reduced oil depletion by over three times after 50 cycles of anti-icing/de-icing tests, providing a resolution for the oil depletion concerns in extended service environments.
To achieve enhanced icephobic performance and durability, a novel design concept involving the integration of phase change liquids with Ni scaffolds and polydimethylsiloxane (PDMS) has been introduced in the multi-phase icephobic construction. Incorporating phase change liquids within the LIS construction allows for heat absorption and release during the icing process, which enhances icephobic performance. Differential scanning calorimetry analysis demonstrated that samples with phase change liquids have a phase change enthalpy of 3.2 J/g for groundnut oil and 3.8 J/g for coconut oil, respectively. As a result of the heat release during the phase change process of the incorporated phase change liquids, the surface temperature of the sample increased, resulting in a delayed ice formation of the supercooled water droplet. The observed freezing time of the droplets on the sample surface was 7-8 times longer than that observed on aluminum alloy. Solidification of the phase change liquids occurred at a low temperature, leading to a concurrent reduction in oil depletion during the de-icing process. This effect was confirmed from the weight maintenance ratio of samples, which remained unchanged even after undergoing 50 cycles of anti-icing/de-icing tests.
The introduction of phase change liquids has been demonstrated to be a viable strategy for enhancing the anti-icing performance of icephobic surfaces. A high-quality icephobic surface should encompass multiple facets of icephobicity, such as anti-icing performance, de-icing ability, and mechanical stability. It is noteworthy that achieving all of these requirements simultaneously is a formidable challenge. To address this issue, a potential icephobic structure has been proposed, which incorporates Ni scaffolds with ice depressing liquid and a polydimethylsiloxane (PDMS) matrix. The ice depressing liquid utilized in this study included glycol and glycerol. The incorporation of ice depressing liquid into the surface layer led to an increase in the amount of hydroxyl groups present, resulting in a notable reduction in the freezing point of supercooled droplets at the liquid-solid interfaces. Furthermore, samples containing ice depressing liquid exhibited a considerable delay in the onset of icing, with respective times of 153.7 ± 2.5 s and 209.7 ± 4.5 s. The results of anti-icing tests provided evidence of the efficacy of ice depressing liquid in reducing the icing point temperature. Upon the sample preparation, the glycol and glycerol in the ice depressing liquid underwent volatilization, leading to the formation of internal porosities within the PDMS. Despite this, the surface morphology of the samples remained smooth and intact. The presence of these internal pores could increase the difference in elastic modulus between the polymer and metallic scaffolds, thus facilitating the initiation of micro-cracks at the ice-solid interfaces and aiding in ice detachment from the sample surface. Consequently, the ice adhesion strength was reduced to below 2 kPa, in contrast to 29.8 ± 2.9 kPa observed for Ni-PDMS samples. Moreover, the results indicated that the de-icing ability of the samples remained stable throughout cyclic icing/de-icing tests.
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