Development of electrospun multifunctional fibrous structures for icephobic and superhydrophobic applications

Tas, Mahmut (2022) Development of electrospun multifunctional fibrous structures for icephobic and superhydrophobic applications. PhD thesis, University of Nottingham.

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Icephobicity is defined as the ability of a solid surface to prevent ice accumulation or the potential of repelling ice from the surface. On the other hand, superhydrophobicity is a physical property of a surface, which means lacking affinity for water, and tending to repel water. Although these two surface properties have critical application areas such as energy harvesting systems, transportation, corrosion resistance coatings and friction reduction, fabricating superhydrophobic and icephobic surfaces is still a big challenge due to the lack of scalable, straightforward, and cost-effective production methods. Moreover, integrating additional functions, including electromagnetic interference (EMI) shielding and electrical conductivity to these materials to achieve multifunctionality, enables many modern applications, such as EMI shielding protective devices and power transmission systems.

Electrospinning is one of the most commonly used methods to produce nano-sized polymeric fibrous membranes or coatings. Unique properties such as high surface-to-volume ratio, high porosity interconnected open pore structures, and adjustable pore sizes make electrospun membranes irreplaceable. However, the potential of using the electrospinning method to produce superhydrophobic and icephobic surfaces is still not investigated in depth. Although there are some studies on the superhydrophobic application of electrospun membranes, considerable challenges remain, such as expensive chemicals, low reproducibility, complex production techniques, and the necessity of a post-treatment or functionalization step. Moreover, electrospun membranes may be a good candidate for icephobic applications based on the Cassie-Baxter icing state or specific material design such as slippery liquid-infused porous structures (SLIPS). In the Cassie-Baxter icing state, water does not penetrate the details of roughness but sits on the air pockets, which provides a low icing area between the ice and the surface, resulting in a lowered work of adhesion of ice. However, no report has been found that explores the potential of the electrospinning method for icephobic applications. In this thesis, the potential of using electrospinning method to fabricate superhydrophobic and icephobic surfaces has been explored.

Polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HFP), which is a low surface energy polymer, was used to explore the potential of using electrospinning method to design a one-step production method of superhydrophobic surfaces without a post-treatment or nanofiller by only changing the production parameters of electrospinning. The proposed method has significant benefits such as shortened processes, less material use, and low-cost production compared to multistep methods reported in the literature. Moreover, the roles of each parameter on surface topography, contact angle, and fibre formation have been discussed. Superhydrophobicity has been achieved thanks to the synergetic effect of the roughness and the low surface tension of the polymer. Additionally, the lowest contact angle hystereses were less than 10°, which is one of the requirements of superhydrophobicity and indicates good mobility of the water droplet on the surface, thanks to the Cassie-Baxter state exhibited.

Since the electrospun PVDF-co-HFP nanofibre membranes fabricated had a good porosity and oleophilic nature, their potential as the porous part of the SLIPS has been explored. The designed structure exhibited exceptional icephobic properties (lower than 1 kPa, one of the lowest ice adhesion strengths reported in the literature) with smooth surface topography and decreased water contact angle. As the water droplet sat completely on a thin film of lubricating liquid thanks to encapsulated regime achieved, ice adhesion strength was reduced significantly. It was also found that these SLIPS had outstanding flexibility and transparency (>90%), resulting from refractive index matching of polymer used and lubricants.

Moreover, a novel multifunctional electrospun membrane was designed and produced for outdoor EMI shielding applications, using recycled polyethylene terephthalate (r-PET) instead of virgin polymers to widen the horizon of using recycled materials. A two-step production process has been applied, which consisted of (i) fabrication of r-PET/magnetite electrospun membranes and (ii) surface modification by fluorinated silane functionalized SiO2 nanoparticles (FSFS). The coaxial waveguide method, a common method to investigate EMI shielding efficiency, was used to investigate EMI shielding properties, and it was found that 20 wt.% magnetite-loaded nanofibre membrane had an EMI shielding efficiency of 22 dB, which was equivalent to above 99% shielding efficiency between 400 MHz and 6 GHz. After FSFS treatment, the nanofibre membrane exhibited Cassie-Baxter state resulted in less than 5° of contact angle hysteresis and approximately 50 kPa ice adhesion strength, thanks to lower surface energy and hierarchical topography, which was beneficial for both icephobic and superhydrophobic performance.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hou, Xianghui
Ahmed, Ifty
Xu, Fang
Keywords: Icephobicity; Superhydrophobicity; Electromagnetic interference shielding; Electrical conductivity; Electrospinning; Surface energy polymer; Nanofibre membrane
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Mechanical, Materials and Manufacturing Engineering
Related URLs:
Item ID: 68285
Depositing User: TAS, MAHMUT
Date Deposited: 19 Apr 2024 10:19
Last Modified: 19 Apr 2024 10:19

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