An investigation into the anti-icing properties of fabrics used for the outer layer of firefighter clothing

Abstract

The anti-icing properties of fabrics can be considered as involving two parts, the super-hydrophobic property and the ease of ice removal property. In this study, a super-hydrophobic surface was built on to the outer layer of firefighter clothing using nano-silica, C₁₃H₁₃F₁₇O₃Si, C₁₉H₄₂O₃Si and PU-2540 using a coating method. This coating stops water drops from staying on the fabric surface easily. At the same time, an ultra-smooth surface was built on to the super-hydrophobic surface already created on the fabric using perfluoropolyethers (PFPE) oil by a dipping method, which adds an ice removal function to the fabrics. The anti-icing properties of the samples prepared in the research described in this paper have been investigated using field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), ease of ice removal property tests and static water contact angle analysis. At the same time, the thermal protective performance (TPP) of the samples, before and after super-hydrophobic treatment, was studied by a TPP tester. Results show that the super-hydrophobic coating with an ultra-smooth surface can significantly increase the anti-icing properties of the fabrics used for the outer layer of firefighter clothing. C₁₃H₁₃F₁₇O₃Si and C₁₉H₄₂O₃Si can improve the hydrophobic properties of the coating. The anti-icing coating in this paper can increase the TPP of the fabrics.

Keywords

anti-icing properties super-hydrophobic property ease of ice removal property firefighter clothing ultra-smooth surface

Damaged crops, collapsed power lines and other features of massive destruction can result from the dramatic effects of icing. Ice accretion on surfaces has received much attention in recent years. This phenomenon is a major problem affecting a variety of industries, and for years it has remained a serious hazard for human society. Moreover, ice accumulation can become a serious problem for workers exposed to cold conditions, especially in cold regions of Asia, North America or Europe. Consequently, the textile industry has been called upon to find ways to combat the problem of ice accumulation, particularly with regard to personal protective equipment. Regarding dangerous work such as, for example, in the work of a firefighter, unrestricted mobility is of paramount importance. The effect of ice formation on clothing is to restrict this mobility, which can bring serious consequences.

At present, chemical, thermal and mechanical methods are actively used for ice removal. The chemical de-icing method delays the freezing process by applying special salts, which reduce the freezing point of water, to the surface of the material. The use of these salts can ease the traffic jams caused by ice on road surfaces in winter, but is a short-term method with a large dosage required. If the salts are used improperly, it can lead to environmental pollution and equipment corrosion.¹ The thermal de-icing method uses heat sources to keep the surface temperature of the materials above freezing point, to prevent the freezing process. This method requires a strong electromagnetic beam, which is difficult to apply, and it cannot be widely used because of the high cost and the low efficiency.² The mechanical de-icing method uses manual or automatic machinery to remove the ice from the surface of the materials. It is more convenient than the thermal and chemical methods, but not very efficient. What is more, in the process of mechanical de-icing, materials will be damaged irreversibly, and the service life of equipment will shorten.³ These active ways to fight against ice accumulation are time-consuming, inefficient, costly and environmentally unfriendly. Therefore, the invention of passive ways to prevent ice and frost accretion is highly desirable. As a method of resolution, investigation techniques to remove the accumulated ice from a solid surface have attracted much attention.

It is well known that a super-hydrophobic surface may provide a promising ice-phobic system. At present, the most widely used method to build a super-hydrophobic surface is to construct a structure similar to the surface of lotus leaves.⁴ The lotus leaf exhibits self-cleaning characteristics owing to super-hydrophobicity resulting from the dual-scale hierarchical structure and the chemical composition, as well as low adhesion to the water droplet. Accordingly, lotus-like super-hydrophobic materials also possess self-cleaning properties. The air pockets that are trapped between the water droplet and the nanostructured surface lead to formation of composite interfaces of solid/air/liquid, thereby allowing the water droplet to immediately roll off, simultaneously carrying away the contaminants adhering to the surface.^5–8

However, recent studies showed that after frost formation, ice adheres more strongly to textured surfaces than to smooth surfaces.^9–11 Bodurogu S et al. reported the control of the adhesive properties of several hydrophobic polymer films deposited by a bottom-up process based on oblique angle deposition. The experiments showed the surface obtained to have both good super-hydrophobicity and strong adhesion.¹² For this reason, it does not mean materials will possess anti-icing properties if they have only super-hydrophobic properties. Ice removal under natural forces can be aided by engineering the surface chemistry and topography to reduce ice adhesion. Specifically, these benefits are attained by the use of low-surface-energy coatings^13–18 and are further enhanced through the addition of surface topography.^19–27

Recently, textured surfaces impregnated with a liquid lubricant have generated much interest because of their remarkable slippery properties. These lubricant-impregnated surfaces have been shown to provide self-cleaning properties, repelling a variety of liquids.^28–32 Furthermore, it was recently reported that nanostructured surfaces infused with perfluorinated fluids exhibit remarkable anti-icing performance that is independent of the underlying texture when compared with hydrophobic and super-hydrophobic surfaces.^33–35

In the research reported in this paper, we developed a SLIPS (Slippery Liquid-Infused Porous Surfaces) analogous material based on fluorinated-oil-infused PU-2540 and nano-silica particles for anti-icing coating on fabrics for firefighter clothing. Nano-silica particles modified with C₁₃H₁₃F₁₇O₃Si were introduced into the material to offer the surface a nano-sized roughness to mimic a super-hydrophobic surface. A C₁₉H₄₂O₃Si coating layer was used to obtain improved super-hydrophobic properties. Furthermore, a perfluoropolyethers (PFPE)-oil-infused coating layer was used to obtain an ultra-smooth surface with ease of ice removal properties for our materials. The coating produced in these experiments showed a weak interaction with ice and significantly reduced ice adhesion strength. At this reduced adhesion strength level, the attached ice may detach and fall off under natural forces or be easily removed while consuming little energy. Moreover, the preparation of this type of coating is very simple and cost-effective.

Experimental method

Materials

The commercially available and commonly used materials in the thermal protective clothing and anti-icing field were selected. Nomex-IIIA fabrics were used as the base fabric in the coating experiment. Nano-silica particles were used to build the super-hydrophobic structure. C₁₃H₁₃F₁₇O₃Si and KH-550 were used to modify nano-silica particles, C₁₉H₄₂O₃Si was chosen for the wax crystal in the super-hydrophobic structure, PU-2540 was chosen to make the coating liquid and PFPE oil was chosen to build the ultra-smooth surface. The basic properties of the materials are described in Tables 1 to 3. All the samples were preconditioned for 24 h at a standard condition of 21℃ and 65% relative humidity before testing.

Table 1.

Structural features of the tested fabrics

Fabric name	Fiber content	Fabric structure	Weight (g/m²)	Manufacturer
Nomex-IIIA	93% Meta-aramid/5% Para-aramid/2% Antistatic	Twill	210	Shanghai SRO Group Limited Company

Table 2.

Basic description of the particles

Particle name	Chemical formula	Particle size (nm)	Manufacturer
Nano-silica	SiO₂	20–30	Shanghai SRO Group Limited Company

Table 3.

Basic properties of the materials

Material name	Chemical formula	Product name	Solid content	Density (g/cm³)	Manufacturer
FAS-17	C₁₃H₁₃F₁₇O₃Si	1H,1H,1H,2H-Perfluorodecyl trimethoxysilane	98%	1.53	Shanghai MACKLIN Reagent Company
KH-550	NH₂(CH₂)₃Si(OC₂H₅)₃	Silane coupler	98%	0.95	Shanghai MACKLIN Reagent Company
PFPE oil	[CF(CF₃)CF₂O]_x(CF₂O)_y	Perfluoropolyethers		1.89	DuPont $R$ Company
C₁₉H₄₂O₃Si	C₁₉H₄₂O₃Si	Hexadecyltrimethoxysilane	96%	0.89	Shanghai MACKLIN Reagent Company
PU-2540	–	Polyurethane-2540	40%	1.04	Guangzhou Yuheng Materials Limited Company
Ethanol	C₂H₅OH	/	99.5%	0.79	Tianjin Baina Chemical Co. Ltd

Surface modification of the silica particles

Nano-silica particles were modified with a mixed solution composed of KH-550, C₁₃H₁₃F₁₇O₃Si and ethanol to improve their hydrophobic properties and their dispersibilities in the coating liquid. Five grams of nano-silica particles was reacted with 0.6 ml of C₁₃H₁₃F₁₇O₃Si, 0.67 ml of KH-550 and 15 ml of ethanol at room temperature for 2 hours with magnetic stirring.

Preparation of super-hydrophobic coatings

Fifteen milliliters of PU-2540, 55 ml of ethanol and 5 g of modified nano-silica particles were mixed using a speed-mixer at a speed of 3000 rpm for 15 minutes. The mixed resin was coated on a piece of Nomex-IIIA fabric using a knife coater to produce a super-hydrophobic surface. The coated specimens were evaporated under ambient conditions for 1 hour to give them a preliminary curing, and then they were cured using an air dry oven under a programmed temperature sequence (60 minutes at 120℃). Ten milliliters of C₁₉H₄₂O₃Si was placed in a beaker, then the cured specimens were dipped in the beaker for 30 minutes under ambient conditions. After dipping, the specimens were cured using an air dry oven under a programmed temperature sequence (60 minutes at 120℃). All the cured specimens were kept in desiccators until they were used or tested to avoid dust contamination.

Preparation of ultra-smooth coatings

Ten milliliters of PFPE oil was placed in a beaker, and then the super-hydrophobic samples prepared in the previous stage were dipped in the PFPE oil for 1 minute under ambient conditions. After dipping, the samples were taken out and dried while held vertically at room temperature until no oil drops remained visible. All the cured specimens were kept in desiccators until they were used or tested to avoid dust contamination.

General tests

The surface topology of the specimen was observed by field emission scanning electron microscopy (FESEM) (Hitachi S4800, Japan). The dispersity of the coating liquid was checked by Transmission electron microscope (TEM) (Hitachi H7650, Japan). Static contact angle was evaluated by a video optical contact angle measuring instrument (OCA15 Pro, Germany). The testing number of the static contact angle test was 10 times, and the average result was used for evaluation/discussion. The ease of ice removal property of the samples was tested by equipment independently developed by our research group.³⁶ The testing number of the ease of ice removal property of the samples was five times, and the average result was used for evaluation/discussion. X-ray photoelectron spectroscopy (XPS) was carried out using an X-ray photoelectron spectrometer (K-alpha, USA). The thermal protective performance of the specimens was evaluated by thermal protective performance (TPP) test apparatus (LLC Whitepine Roas, USA).

Working principle of the ease of ice removal (EIR) property tester

The method used to test the EIR property of textile fabrics is one of the main obstacles in this area. Current research shows that an universally accepted industry standard is still lacking to evaluate the EIR properties of textile fabrics, and consequently, there is the need to develop a machine to test how easy it is to clear the ice.³⁶ The researcher created a new phrase for this property, namely the EIR property.

As shown in Figure 1, the EIR property tester consists of a lifting platform, two support pillars and the sample holder. Moreover, there are two different types of containers. The reason for this is the two different types of forces that arise in cleaning the ice from the clothing.

Figure 1.

Mode of operation of the ease of ice removal tester.

The first container (Figure 2), which has a slit, is used to test the tangential EIR time on an iced sample. The sample size needs to be 75 × 15 mm. The maximal volume of the container is 10 cm³ but only 9 cm³ of water is added. This is because the expansion ratio of water to ice is 10:9, which means that after freezing, the container is filled to capacity with 9 cm³ of water. The next step after adding water to the container is to clip the sample onto the sample holder. When the EIR property tester is prepared, it is placed in an upright freezer for around 3 hours to ensure complete icing. In this time, the water becomes ice and increases to a volume of 10 cm³. This means that the sample is contained within the ice for 3 hours. Then, the machine is placed into the dryer. After closing the dryer, the time is recorded until the moment that the containers begin to drop. The EIR times can be established and compared using this method, as the sooner the container drops, the better the EIR property is.

Figure 2.

Container to test the tangential ease of ice removal (EIR) time. (a) Container; (b) simulation.

The second container (Figure 3) is used to test the horizontal (normal force) EIR time for an iced sample. The method used with this container is the same as for the first container but there are some differences concerning the sample preparation and configuration in the container. The size of the sample is larger, namely 180 × 40 mm. Moreover, the sample is located horizontally on the water. The two edges of the sample, which are protruding when the cover is placed on the container, are folded up and clipped together on the sample holder. After this preparation, the following steps are the same as for the first container.

Figure 3.

Container to test the horizontal ease of ice removal (EIR) time. (a) Container; (b) simulation.

Experimental conditions

When the EIR property tester was prepared, it was placed in an upright freezer at a temperature of –40℃. Then the machine was placed in the dryer at a temperature of 50℃. When testing the TPP value of the samples, the heat flux was 2.04 W. All the other experiments were carried out at room temperature.

Results and discussion

Surface modification of nano-silica particles

Nano-silica particles are widely used for building super-hydrophobic coatings. Unfortunately, nano-silica particles easily agglomerate because of the surface interactions involving hydrogen bonding and van der Waals forces, which leads to a decrease in the performance of the coatings. This agglomeration needs to be avoided. Surface modification treatment, shearing force through stirring and ultrasonication treatment are the most widely used methods to achieve this. In this research, C₁₃H₁₃F₁₇O₃Si was used as the modifier to increase the dispersibility and hydrophobicity of nano-silica particles, and the inorganic powder particles were nano-silica. However, the affinity between C₁₃H₁₃F₁₇O₃Si and nano-silica particles was not big enough to couple them together. KH-550 can solve this problem. KH-550 is a kind of silane coupling agent, the chemical formula of which is NH₂CH₂CH₂CH₂Si(OC₂H₅)₃. In the process of coupling, KH-550 reacted with H₂O to form a kind of silanol (Figure 4 (a)). Then, the silanol reacted with the hydroxyl on the surface of the nano-silica particles to form -SiO-M (M represents the surface of nano-silica particles) covalent bonds (Figure 4(b)). During this process, C₁₃H₁₃F₁₇O₃Si particles interrelated with each other to form a network of membranes covering the surface of the nano-silica particles, making the inorganic powder surface organic (Figure 4(c)). These modified nano-silica particles contain and generate mass fluorine atoms on the surface, so that the surface energy will be lower and will offer improved dispersibility and hydrophobicity for the particles.

Figure 4.

(a–c) The coupling process of C₁₃H₁₃F₁₇O₃Si and nano-silica particles.

The success of the surface modification was confirmed by XPS. The spectra of the pristine silica and the modified version are compared in Figure 5. The characteristic absorption peak of fluorine showed a significant rise after being treated with C₁₃H₁₃F₁₇O₃Si. The result showed that there was a certain amount of fluorine on the raw fabric. This is because the fabric used is made from Nomex® IIIA, which is treated with fluorine-containing compounds in the finishing process.

Figure 5.

X-ray photoelectron spectroscopy (XPS) results of the samples.

Proportion of super-hydrophobic coating

Fabrics with good anti-icing properties should have the property that water drops cannot stay on the surface of the fabrics easily. Super-hydrophobic coating can offer this function to fabrics. In this study, a super-hydrophobic surface was built on the outer layer of firefighter clothing with modified nano-silica, C₁₉H₄₂O₃Si, ethanol and PU-2540 using a coating method. PU-2540 is a new type of polyurethane system that is widely used in the textile finishing field. This kind of polyurethane system can give the fabric a soft and plump feel and can improve the resilience and heat resistance of the fabrics. Furthermore, PU-2540 is low cost, non-toxic and easy to handle. PU-2540 provides almost all the functions we need, so it was chosen as the matrix resin for this work.

To build a good super-hydrophobic surface, some pre-experiments were carried out. It is very difficult for nano-silica to disperse in PU-2540, but it is easily dispersed in ethanol. If there is too much ethanol in the coating liquid, its viscosity will be so low that the coating process cannot be carried out. On the other hand, if the amount of ethanol is too low, the proportion of PU-2540 will be very high. PU-2540 is very viscous, and if the amount of ethanol is inadequate, the nano-silica cannot disperse sufficiently, which will prevent formation of the lotus leaf structure. However, if there is not enough PU-2540, the nano-silica will not adhere to the fabric successfully. The results showed that 55 ml of ethanol and 15 ml of PU-2540 is optimum. With regard to the amount of modified nano-silica particles, if too little, the lotus leaf structure would not be built successfully, and if too much, severe cracking would happen during the drying process. In this research, the amount of modified nano-silica particles used was 5 g. After dispersing in the polymer matrix, the particle size of the modified nano-silica particles was verified by TEM as shown in Figure 6. The number of counted particles in this photo was 78, the average diameter was 61 nm and the standard deviation was 55.4.

Figure 6.

The particle size verified by TEM.

In this experiment, we set the coating machine to different thicknesses of coating. When the thickness of the coating was 0.5 mm, the hydrophobic property of the samples showed an obvious decrease. This was because the nano-silica particles in the coating liquid agglomerated poorly during the drying process. The thicker the coating, the easier the nano-silica particles could agglomerate. The results shown in Figure 7 indicate that the optimal thickness of the coat was 0.3 mm.

Figure 7.

Contact angle of the samples with different thickness.

Super-hydrophobic property of the samples

If the contact angle of the material is over 150°, this type of material can be called super-hydrophobic. As shown in Figure 8, the contact angle of the coated sample is 153.1°, which has already achieved the super-hydrophobic level. The contact angle of the untreated sample is only 127.4°, which is at a normal hydrophobic level. The better the hydrophobic property, the more difficult it is for the water drops to stay on the surface of the fabric. ‘No water, no ice.’ The hydrophobic property of the coated sample is better than the untreated sample, which will provide better anti-icing properties for the fabric.

Figure 8.

The contact angle of the samples. (a) Untreated sample; (b) coated sample.

The surface morphology of the sample was investigated by FESEM as shown in Figure 9. The results showed that the lotus leaf structure with micro- and nano-protrusions had been built successfully. This type of structure can provide the super-hydrophobic properties for the fabric.

Figure 9.

The surface morphology of the samples. (a) Super-hydrophobic sample (10 kv × 1 k); (b) super-hydrophobic sample (10 kv × 20 k).

Ultra-smooth surface with PFPE oil

Micro- and nano-protrusions are required for a super-hydrophobic surface as shown in Figure 10(a). Although this type of surface structure can prevent the water drops from remaining on the surface of the fabric, it has proved ineffective in preventing ice formation on the surface under conditions of lower temperature and high humidity. It was found that moisture easily condensed and then formed icicles in the interspaces between the micro- and nano-protrusions of a super-hydrophobic surface. These icicles further promoted the icing process on the surface to root the surface ice into the rough surface structure as shown in Figure 10(b).³⁷ Extra force would be required to break down this icicle-rooted ice layer on the surface.

Figure 10.

The micro- and nano-structure of the samples. (a) Water on Super-hydrophobic surface; (b) ice on super-hydrophobic surface; (c) ice on ultra-smooth surface.

In this paper, the ultra-smooth material is designed by infusing PFPE oil into the porous structure of a super-hydrophobic surface as shown in Figure 10(c), so that the topological surface is smooth. The material used was PFPE, a transparent Krytox® GPL105 oil. The most important reason for using this type of oil is that it tolerates very cold conditions, e.g. –40℃, as well as extremely hot conditions, e.g. 204℃, and is therefore suitable for the application envisaged in this investigation. The samples described in this paper have both EIR and super-hydrophobic properties, and the coating contains two layers. The first layer in contact with the fabric is super-hydrophobic and the second layer made up of PFPE oil could provide the EIR property. When water drops fell on the super-hydrophobic layer without PFPE oil, the contact angle was very high, as shown in Figure 11(b). When the water drops fell on the Liquid-Infused Porous Surfaces (LIPS), water drops touched the PFPE oil first. PFPE oil is hydrophobic, but not super-hydrophobic, so the contact angle was only about 121.7° (Figure 11(a)).

Figure 11.

The contact angle of the samples. (a) Ultra-smooth sample; (b) super-hydrophobic sample.

The surface morphology of the sample was also investigated by FESEM, as shown in Figure 12. The results showed that the super-hydrophobic surface was covered by PFPE oil completely and the lotus leaf structure with micro- and nano-protrusions was still there. This type of structure can provide the fabric with EIR properties which will improve its anti-icing properties at the same time.

Figure 12.

The surface morphology of the samples. (a) Ultra-smooth sample (10 kv × 1 k); (b) ultra-smooth sample (10 kv × 9 k).

EIR properties of the samples

Fabrics with good anti-icing properties should have the function that the ice on the surface of the fabrics can be easily cleared, which is referred to as the EIR property in this paper. The EIR properties of the samples were tested by an ease of ice removal property tester. The results are shown in Table 4.

Table 4.

The EIR properties of the samples

Sample type	Untreated samples		Super-hydrophobic samples		Ultra-smooth samples
Force type	Tangential	Normal	Tangential	Normal	Tangential	Normal
Drop time (s)	541	750	510	650	355	428

As shown in Table 4, a super-hydrophobic coating can slightly improve the EIR properties of the samples. Fabrics are porous materials. During the process of being frozen on fabrics, water will permeate into the holes and become icicles. The mechanism proposed involves the super-hydrophobic coating covering most of the holes on the fabric, so that the amount of icicles, which will increase the contact force between the ice and the fabric, will decrease. The ultra-smooth coating can improve the EIR properties of the samples for obvious reasons. The mechanism is shown in Figure 13.

Figure 13.

The anti-icing mechanism of the ultra-smooth surface. (a) Water on ultra-smooth surface; (b) oil migration on ultra-smooth surface; (c) ice–oil diffusion on nano-icicles.

When the water drops fall on the LIPS, they will touch the PFPE oil first (as shown in Figure 13(a)). Then the water drops will form an oil–water (OW) interface together with the PFPE oil. In fact, the OW interface is not a completely separated interface but a transition zone between pure oil and pure water. In this interface, there is a certain concentration of ionic surfactant naturally. The surfactant will migrate from water to oil. During the migration, due to the slow diffusion speed, the local concentration of the OW interface increases. When the equilibrium state is broken, some spontaneous changes will happen in the OW interface. These changes will create a property shock between the interfaces. Environmental factors, such as temperature and mechanical motion, will promote this shock, and this shock results in the penetration of water and PFPE oil (as shown in Figure 13(b)).³⁸ As the temperature decreases, these water drops start to freeze. In order to remove the nano-icicles, some of the PFPE oil in the nano-holes will migrate to the surface, then the oil will try to cover the nano-icicles (as shown in Figure 13(c)). With the work of extra forces, the nano-icicles covered by PFPE oil will be removed. Furthermore, because of the presence of the PFPE oil, parts of the ice cannot contact the surface of the super-hydrophobic coating directly. As the temperature rises, the ice will melt, and the PFPE oil will allow the ice on the surface of the coating to clear easily. In this way, the ultra-smooth surface with PFPE oil can increase the EIR property of the samples.

Thermal protective properties of the samples

Because the samples in this study will be used for making firefighter clothing, the thermal protective properties are very important. As discussed earlier, the ultra-smooth coating designed in this research can improve the anti-icing properties of the samples. Whether the coating affects the thermal protective properties was also studied. The TPP test is designed to evaluate the thermal protective performance of clothing materials. When the test starts, TPP tester will record the heat flux changes of the skin sensor. The data will be used to build a curve in a planar reference frame with the heat flux as the Y-axis and the time as the X-axis. As time goes on, the curve will intersect a standard curve (Stoll curve) at a point.³⁹ The X value of this point represents the TPP time of the sample. TPP time means the minimum time for the skin sensor to get a second-degree burn. By multiplying TPP time and the standard heat flux (84 kW/m²), we can get the TPP value.

As shown in Figure 14, samples with the ultra-smooth coating were more resistant to damage by heat. The coating contains nano-silica with a high melting point. Before the heat contacts the fabric, it will contact the coating first. As the coating is damaged, the nano-silica will absorb much heat, and, in this way, the fabric is protected. When bended, the untreated samples after TPP testing can be broken in every direction, but the coated samples cannot be broken easily.

Figure 14.

Damaged condition of the samples. (a1) Untreated sample before TPP test; (a2) untreated sample after TPP test; (b1) ultra-smooth sample before TPP test; (b2) ultra-smooth sample after TPP test.

The TPP test results are shown in Table 5. Comparing the thermal protective property times, the average values for the samples show a difference of 0.54 seconds, with the coated sample having the longer TPP time. Moreover, the TPP value for the uncoated samples is 8.62 kW·s/m² whereas the TPP value is 9.73 kW·s/m² for the coated samples.

Table 5.

TPP test results of the samples

	Heat flux (W)	TPP time (s)	TPP value (kW·s/m²)
Sample
Untreated samples	2.04	4.23	8.62
Coated samples	2.04	4.77	9.73

Conclusions

In this study, a type of super-hydrophobic coat was prepared from PU-2540 with the addition of surface-modified silica particles to produce a nanoscale surface roughness. C₁₉H₄₂O₃Si was used to give the samples another coat with a low surface energy. Fifteen milliliters of PU-2540, 55 ml of ethanol and 5 g of modified nano-silica particles made up the coating liquid. This surface has a low interaction with water and ice, leading to a low surface energy and highly hydrophobic properties with a contact angle of 153.1°. Then, a type of ultra-smooth coating was prepared from the super-hydrophobic coating, and subsequently, PFPE oil has been introduced to further increase the anti-icing properties of the samples. The ultra-smooth coating can improve the EIR properties of the samples in an obvious way.

Surface modification, ultrasonic treatment and stir are the most widely used ways to improve the dispersibility of particles in a liquid. In this study, these three kinds of methods were adopted, and among which, a method to modify nano-silica with C₁₃H₁₃F₁₇O₃Si and KH550 was introduced. The results showed that, compared to other modifiers, C₁₃H₁₃F₁₇O₃Si not only increases the dispersibility of the particles in the liquid, but also the hydrophobic properties of the nano-silica particles because of the presence of fluoride.

A specially created machine has been introduced to test the EIR properties of the samples. This machine can simulate two types of forces between the ice and the fabric, and the drop time of the containers is set as the parameter to reflect the EIR properties of the samples. Compared with the other machines in this field, this machine is more economical and easier to use. In this study, the EIR properties of the samples were successfully tested by this machine. The results show that the ultra-smooth coating can improve the EIR properties of the samples in an obvious way. Compared with the untreated samples, the drop time decreases from 541 s/750 s (tangential force/normal force) to 355 s/428 s.

The ultra-smooth coating can also protect the fabrics from heat and can increase the TPP of the fabric. The TPP value for the uncoated samples is 8.62 kW·s/m² whereas the TPP value is 9.73 kW·s/m² for the coated samples. Compared with the uncoated samples, the damage to the coated samples is less.

The anti-icing properties of clothing are not only useful for firefighter clothing but also for ski wear, down jackets, etc., which can be sold to consumers living in cold regions. The ultra-smooth coating prepared in this study can also be applied to other clothing and fibers. More work needs to be done on this topic. In the future, the durability and air permeability of ultra-smooth coats could be studied, and mathematical models could be built to study the force changes between ice and fabrics.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

References

Fay

Shi

. Environmental impacts of chemicals for snow and ice control: state of the knowledge. Water Air Soil Poll 2012; 223(5): 2751–2770.

Jiang

Zhang

. De-icing and anti-icing of transmission lines. High Volt Eng 1997; 1: 73–76.

Egbert

Schrag

Bernhart

et al.

An investigation of power line de-icing by electro-impulse methods. IEEE Trans Power Del 1989; 4(3): 1855–1861.

Neinhuis

Barthlott

. Characterization and distribution of water-repellent, self-cleaning plant surfaces. Ann Bot 1997; 79: 667–677.

Guo

et al.

Fabrication of functional super-hydrophobic engineering materials via an extremely rapid and simple route. Chem Commun 2015; 51: 6493–6495.

Fürstner

Wilhelm

. Wetting and self-cleaning properties of artificial super-hydrophobic surfaces. Langmuir 2005; 21(3): 956–961.

Jiang

Zhenguan

Rahmat

et al.

Two-Step process to create “roll-off” super-amphiphobic paper surfaces. ACS Appl Mater Interfaces 2017; 9(10): 9195–9203.

Ming

Benthem

et al.

Super-hydrophobic films from raspberry-like particles. Nano Lett 2005; 5(11): 2298–2301.

Varanasi

Deng

Smith

et al.

Frost formation and ice adhesion on super-hydrophobic surfaces. Appl Phys Lett 2010; 97(23): 234102–234103.

10.

Kulinich

Farhadi

Nose

et al.

Super-hydrophobic surfaces: are they really ice-repellent. Langmuir 2011; 27: 25–29.

11.

Chen

Liu

et al.

Super-hydrophobic surfaces cannot reduce ice adhesion. Appl Phys Lett 2012; 101: 111603–111603.

12.

Bodurogu

Cetinkaya

Dressick

et al.

Controlling the wettability and adhesion of nano-structured poly-(p-xylylene) films. Langmuir 2007; 23(23): 11391–11395.

13.

Raraty

Tabor

. The adhesion and strength properties of ice. Proc R Soc A 1958; 245: 184–201.

14.

Sayward JM. Seeking low ice adhesion. Hanover, NH: Engineering Research Branch, CRREL, 1979, p. 88.

15.

Saito

Takai

Yamauchi

. Water-and ice-repellent coatings. Surf Coat Int 1997; 80: 168–171.

16.

Petrenko

Peng

. Reduction of ice adhesion to metal by using self-assembling monolayers (SAMs). Can J Phys 2003; 81: 387–393.

17.

Dotan

Dodiuk

Laforte

et al.

The relationship between water wetting and ice adhesion. J Adhes Sci Technol 2009; 23: 1907–1915.

18.

Meuler

Smith

Varanasi

et al.

Relationships between water wettability and ice adhesion. ACS Appl Mater Interfaces 2010; 2: 3100–3110.

19.

Cao

Jones

Sikka

et al.

Anti-icing super-hydrophobic coatings. Langmuir 2009; 25: 12444–124488.

20.

Tourkine

Le Merrer

Quéré

. Delayed freezing on water repellent materials. Langmuir 2009; 25: 7214–7216.

21.

Kulinich

Farzaneh

. Ice adhesion on super-hydrophobic surfaces. Appl Surf Sci 2009; 255: 8153–8157.

22.

Meuler

McKinley

Cohen

. Exploiting topographical texture to impart icephobicity. ACS Nano 2010; 4: 7048–7052.

23.

Mishchenko

Hatton

Bahadur

et al.

Design of ice-free nanostructured surfaces based on repulsion of impacting water droplets. ACS Nano 2010; 4: 7699–7707.

24.

Antonini

Innocenti

Horn

et al.

Understanding the effect of super-hydrophobic coatings on energy reduction in anti-icing systems. Cold Reg Sci Technol 2011; 67: 58–67.

25.

Guo

Zheng

Wen

et al.

Ice-phobic/anti-icing properties of micro/nano-structured surfaces. Adv Mater 2012; 24: 2642–2648.

26.

Alizadeh

Yamada

et al.

Dynamics of ice nucleation on water repellent surfaces. Langmuir 2012; 28: 3180–3186.

27.

Jung

Dorrestijn

Raps

et al.

Are super-hydrophobic surfaces best for ice-phobicity. Langmuir 2011; 27: 3059–3066.

28.

Quéré

. Non-sticking drops. Rep Prog Phys 2005; 68: 2495–2532.

29.

Smith J, Dhiman R and Varanasi K. Liquid-encapsulating surfaces: overcoming the limitations of super-hydrophobic surfaces for robust non-wetting and anti-icing surfaces, Baltimore, Maryland, 20-22 November 2011, Session S4.00001. Baltimore: APS.

30.

Wong

Kang

Tang

SKY

et al.

Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature 2011; 477: 443–447.

31.

Lafuma

Quéré

. Slippery pre-suffused surfaces. Europhys Lett 2011; 96: 56001–56001.

32.

Anand

Paxson

Dhiman

et al.

Enhanced condensation on lubricant-impregnated nanotextured surfaces. ACS Nano 2012; 6: 10122–10129.

33.

Smith

Dhiman

Anand

et al.

Droplet mobility on lubricant impregnated surfaces. Soft Matter 2013; 9: 1772–1772.

34.

Kim

Wong

Alvarenga

et al.

Liquid-infused nanostructured surfaces with extreme anti-ice and anti-frost performance. ACS Nano 2012; 6: 6569–6569.

35.

Wilson

et al.

Inhibition of ice nucleation by slippery liquid-infused porous surfaces (SLIPS). Chem Chem Phys 2013; 15: 581–585.

36.

Tianjin Polytechnic University. Referencing styles for journals – a new method. Patent 201710815341.8, China, 2017.

37.

Antonini

Innocenti

Horn

et al.

Understanding the effect of super-hydrophobic coatings on energy reduction in anti-icing systems. Cold Reg Sci Technol 2011; 67(1): 58–67.

38.

Dimon

Kushnick

Stokes

. Resonance of a liquid–liquid interface. J Phys 1988; 49(5): 777–785.

39.

NFPA 1971: 2007. Standard on protective ensembles for structural fire fighting and proximity fire fighting.