Review of the literature on hydro- and icephobic coatings 

Review of the literature on hydro- and icephobic coatings

Hydro- and icephobic SAMs coatings

In order to develop icephobic coatings, various groups of materials or surface treatments can be considered. In this section we focus on the introduction of selfassembled monolayers (SAMs) and their hydro- and icephobic properties. It is possible to alter the surface energy of surfaces by an appropriate surface coating as thin as a few layers of SAMs molecules with -CH3 or -CF3 groups oriented outward to the ice surface. Deposition of self-assembled monolayers is one of the most successful approaches to hydrophobization of hydrophilic surfaces [59-61]. Such molecules usually have a polar unit at one end (head) and a non-polar long saturated hydrocarbon chain on the other end (tail) such as -CH3 or -CF3 groups oriented outward from the coating surface. A typical example is stearic acid . The performance of this treatment has been tested on a number of metal and alloy substrates including aluminum and aluminum alloys, various steels, copper and copper alloys, brass, zinc, and several automotive and aircraft alloys. A widely used class of SAMs is based on n-alkyltrichlorosilane or nalkyltrialkoxysilane molecules which through a combined process of adsorption, hydrolysis and polymerization can lead to  spontaneously assembled and organized alkylsiloxane monolayers at oxide surfaces such as Al2O3, SiO2, SnO2, etc. [62, 28, 64- 65].

Hydro- and icephobic nanoparticles coatings

In this section the hydro- and icephobic properties of various nanoparticles incorporated in polymer coatings are reviewed. There is extensive research on nanoparticles incorporated in polymers such as RTV silicon rubber coatings with TiO2, CeO2 and carbon black, respectively [16, 71]. The adhesion reduction factor (ARF) value of 1 wt. % of CeO2 nanoparticles incorporated in RTV silicon rubber coatings was 7 times lower on this coating than with bare aluminum [72]. A preparation of nanoparticles incorporation (SiO2 and CaCO3) in stearic acid coatings by spraying gave contact angle and CAH values of 160° and 3° , respectively [73]. For the meantime, the results showed that the super-hydrophobic surface became rather hydrophobic at super-cooled temperatures (-10 °C). Super-hydrophobic micro patterned aluminum surfaces were created by chemical etching that it was shown a water contact angle as high as 164 ± 3◦ with a contact angle hysteresis as low as 2.5±1.5◦ on rf-sputtered Teflon-coated etched aluminum substrates [74]. A thin nanostructured silver film with stearic acid demonstrated water contact angle as high as 156° and contact angle hysteresis as low as 5° [75]. A simple method to elaborate fluoro-alkyl-terminated nanostructured superhydrophobic surfaces was provided by depositing a layer of FAS-17 on etched AA2024 surfaces in hot water, which showed good superhydrophobic and self-cleaning properties [76] .

Hydro- and icephobic plasma coatings

Plasma-assisted deposition of thin fluorocarbon, organosilicon and hydrocarbon coatings have also resulted in hydro- and icephobic surfaces [77-79]. A hydrophobic layer was coated on the nanotextured surfaces by means of either the low-temperature CVD or the PECVD [80]. The surface-modified showed ultra water repellency with water contact angles greater than 150° [80]. The created nanostructured patterns on aluminum alloy surfaces by immersion in boiling water, coated with RF-sputtered polytetrafluoroetylene demonstrated a high static CA (164°) and low CAH (∼4°) [81]. A treated Teflon film with oxygen plasma became a super-hydrophobic surface with a contact angle value of ~ 168o [82]. A poly (ethylene terephthalate) (PET) substrate with selective oxygen plasma etching followed by plasma-enhanced chemical vapor deposition using tetramethylsilane (TMS) as a precursor produced a transparent superhydrophobic surface [83].

Hydro- and icephobic heterogeneous coatings (HCs)

In the previous sections the hydro- and icephobic coatings prepared via SAMs, incorporated nanoparticles in polymers, and plasma methods, were reviewed. It was observed that the prepared coatings by the three methods mentioned above included hydrocarbon or fluorocarbon functions named as homogeneous coatings. However, the low surface energy of HCs or surfaces including both hydrocarbons and fluorocarbons have drawn less attention. These types of coatings are a very attractive alternative because they show lower ice adhesion as compared to homogeneous coatings. Basically, using HC the ice structure directly in contact with the surface is disrupted, because the orientation of water molecules depends upon the nature of the material, and consequently ice adhesion force can be reduced. Three important articles close to this work have been published in the field of heterogeneous polymer coatings, where the authors tried to decrease ice adhesion  by applying a HC [25-27]. For instance, two different heterogeneous polymers, polyperfluoroalkylmethacrylate combined with hydrophobic silicon dioxide (A), and also an organopolysiloxane modified with lithium compound (B), have been studied. The ice adhesion values of heterogeneous polymers A and B compared to PTFE were reduced two fold and 25 times, respectively. To explain such behavior, the authors evaluated the lengths of the hydrogen bond to oxygen and fluorine (O—H and F—H) as well as the different interaction energies [26-28] (see Fig. 2.8). They found that there is a slight repulsion between a water molecule and a siloxane group, while a strong attraction was observed between a fluorocarbon group and a water molecule. It should be noted that the water molecule orientations at the surface of fluorocarbon group and at the polysiloxane one were completely different. Consequently, by inducing and creating various disparities (hydrocarbons and fluorocarbons) in terms of energy bonding and water molecule orientation at the molecular level, the ice-solid interface is weakened by the possible creation of a wide range of dislocations and slips in the accumulated ice structure immediately adjacent to the solid surface (ice-solid interface line). The principle is the same as already proposed by Murase et. al and Byrd [26-28]. They have indicated the presence of a synergistic effect caused by the heterogeneity of the polymer coating leading to lower values of ice adhesion strength [26-28].

In theory, their calculation of the enthalpy of the F—H bond gives -50.89 KJ/mol with a bond length of 0.189 nm. For the O—H bond, the enthalpy is equal to -15.65 KJ/mol with a bond length of 0.329 nm. However, by applying heterogeneous surface coatings i.e. F—H and O—H bondings at the same time, the enthalpy and bond length change to -10.28 KJ/mol and 0.307 nm respectively for F—H and to -9.60 KJ/mol and 0.267 nm respectively for the O—H bond [26]. Therefore, it may be concluded that in the case of heterogeneous surfaces, due to the significant increase in the bond length of F—H and eventually the increase in the enthalpy, the overall interaction energy will be greater [26]. It must be mentioned that few studies and uses of such HCs were found in the literature.

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Table des matières

CHAPTER I INTRODUCTION
1. INTRODUCTION
1.1 THE ICING PROBLEM
1.2 ICE ACCUMULATION PREVENTION
1.3 ORIGINALITY OF THE RESEARCH WORK
1.4. OBJECTIVES
1.5 OUTLINE OF THE THESIS
CHAPTER II  BACKGROUND AND LITERATURE REVIEW
2. INTRODUCTION
2.1 A BRIEF REVIEW OF HYDROPHOBIC AND SUPER-HYDROPHOBIC PROPERTIES
2.1.1. Hydrophobicity and contact angle
2.1.2. Super-hydrophobicity and roughness
2.2 ICE ACCUMULATION AND TYPES OF ICE
2.3 REVIEW OF THE LITERATURE ON HYDRO- AND ICEPHOBIC COATINGS
2.3.1. Hydro- and icephobic SAMs coatings
2.3.2. Hydro- and icephobic nanoparticles coatings
2.3.3. Hydro- and icephobic plasma coatings
2.4 HYDRO- AND ICEPHOBIC HETEROGENEOUS COATINGS (HCS)
2.5 CONCLUSION
CHAPTER III  EXPERIMENTS AND TEST PROCEDURE
3. INTRODUCTION
3.1 SUBSTRATE PREPARATION AND CLEANING
3.2 PREPARATION OF HOMOGENEOUS AND HETEROGENEOUS OF SAMS COATINGS
3.3 PREPARATION OF HOMO- AND HETEROGENEOUS NANOPARTICLES COATINGS
3.4 PREPARATION OF HOMO- AND HETEROGENEOUS PLASMA COATINGS THROUGH MASKS
3.5 SAMPLE ANALYSIS AND CHARACTERIZATION
3.5.1. Atomic Force Microscope (AFM)
3.5.2. Optical profilometry analysis
3.5.3. Scanning Electron Microscopy (SEM/EDX)
3.5.4. X-ray photoelectron spectroscopy (XPS)
3.5.5. QUV tester
3.6 WETTABILITY TESTS
3.6.1. Contact angle hysteresis (CAH)
3.6.2. Sliding angle
3.7 ICE ADHESION TEST
CONCLUSION

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