Ice resistant coatings, also know as anti-icing, ice-repellant and icephobic coatings repel water droplets, delay ice nucleation and significantly reduce ice adhesion on surfaces. Ice-resistance is desirable for a variety of surfaces including aircraft (fixed and rotary wing), vehicles, ships, camera lenses, road signs, protective eyewear, buildings, antennae, power lines, and bridges.
The use of ice-resistant coating systems has several advantages over existing methods for mitigating the build-up of ice including:
• no energy required
• can be retrofitted
• enhancement of product value.
• reduction in costs and energy consumption.
• improve performance of technical goods.
• environmentally friendly and cost-effective way to solve the issue of ice formation and accretion.
• mitigate safety concerns and issues.
Ice formation and accretion on surfaces is a major problem in various industries from transportation to energy generation, leading to equipment failure and high energy loss.1 2
To deal with this problem, surface-coatings techniques based on thermal, chemical, and mechanical methods have been implemented to
attain anti-icing properties; however, most of these rely on complicated processes that require expensive equipment and labour-intensive procedures with detrimental environmental consequences. This has opened opportunities for new nanocoatings technologies.
Superhydrophobic coatings
Superhydrophobic surfaces possess extraordinary water repelling properties due to their low surface energy and specific nanometer- and micrometer-scale roughness.3 A superhydrophobic surface is able to repel water droplets completely; such surfaces exhibit water droplet advancing contact angles (CAs) of 150o or higher and sliding angles (SAs) < 10°. The theoretical limit for CAs is 180o. Researchers at ORNL has developed surfaces with CAs of >179o.
Superhydrophobic coatings enhance anti-icing properties by:
• delaying ice formation.4
• enhancing the dynamic anti-icing behaviour of water droplets impacting the SHP surface.5
• reducing the ice adhesion strength.6
Figure 1: Superhydrophobic coatings on glass.
Image: ORNL.
However, a large number of investigations have shown that frost can build up within the micro/nanostructured features of superhydrophobic surfaces under sub-zero conditions, leading to the anchoring of ice, which in turn results in the increase of ice adhesion during icing/deicing cycles. Frost can build up within the micro/nanostructured features of superhydrophobic surfaces under sub-zero conditions, leading to the anchoring of ice, which in turn results in the increase of ice adhesion during icing/de-icing cycle.7 8 9
Also, with regular exposure to weather such as freezing rain, the icephobicity of the coatings decreases to a significant extent after a few thawing freezing/thawing cycles.10 11 12 However, other researchers have since demonstrated that superhydrophobic nanocoatings display high stability against periodic crystallisation of water contacting the coatings.13 14
Omniphobic coatings
Among all the attributes of superhydrophobic coatings, the most challenging is to achieve multi-functionality that includes super-omniphobicity (completely repels both water and oil), high transparency with minimal haze, and mechanical durability. Over the past few years, researchers have proposed oleophobic and omniphobic surfaces that repel most organic liquids, therefore negating the problems faced by superhydrophobic coatings (e.g. coatings are usually fragile, surfaces can be fouled by contaminants, and condensation can induce intrusion).
Surfaces that are capable of supporting non-wetting interfaces for both high and low surface tension liquid droplets are considered to be omniphobic. Most fabricated superhydrophobic micro/nano-structured surfaces are not suitable to support non-wetting states for low surface tension liquids, such as oils and alcohols. To overcome this limitation, researchers have engineered surfaces with topographic features having specialized reentrant geometries, such as:
• inverse trapezoidal.15
• serif-T. 16 17
• mushroom.18 19 20
• micro-hoodoo.21 22
• micro-nail structures. 23
On such surfaces, deposited droplets remain pinned at the sharp edge of the reentrant structures, where the meniscus generates an upward force that resists droplet collapse into the surface cavities, even for low surface tension liquids.
Figure 2: SLIPS technology coating.
Image: Adaptive Surface Technologies, Inc.
One strategy for creating omniphobic surfaces is slippery liquid-infused porous surfaces (SLIPSs) that are “liquid-like” developed at the University of Harvard. Inspired by the Nepenthes pitcher plant. SLIPSs do not require pressure-dependent metastable states but involve dynamic liquid/liquid/vapor contact line motion.24 25 26
Advantages of this approach include functioning under extreme high-pressure conditions, self-healing and anti-icing properties. 27
Phase switching materials
Novel ice-phobic coatings have been developed that employ organophosphorous phase change materials (PCMs). PCMs exist in a passive or dormant state under most environmental conditions, but PCMs undergo solid-solid phase changes over a narrow temperature range slightly below at which ice formation occurs. As ice forms on the surface, some of the latent heat of freezing passes to PCMs. This heat is absorbed by the PCMs and causes local strain on the coating surface and results in removal of the ice. Minimal force (<1psi) is required to remove ice from test surfaces treated with PCM ice-phobic coating technology.
Graphene coatings
Graphene-based de-icing composites and anti-icing coatings are of great interest due to exceptional thermal, electrical and mechanical properties of graphene. Advantages of the use of graphene include:
• Delays ice formation
• Lowers the temperature of the freezing onset
• Prevents fogging
• Transparent
• Extremely lightweight
• Strong and durable
• An efficient conductor.
The use of graphene coatings can accelerate the internal heat transfer of the composite materials, improving the anti-icing and de-icing efficiency of aerospace and wind turbine components.
Figure 3: Graphon Coating for use in conductive heating coatings for de-icing.
Image: CSIRO.
Currently, fibre reinforced polymer composites are increasingly popular in aerospace, automobile and civil engineering industries due to their higher strength and lower weight. However, ice accumulation reduces the advantages that the composite brings to the structure. The electro-thermal system is identified as one of the most promising de-icing systems for polymer composites, as it does not cause delamination and damage to composite structure. However, the application of the electro-thermal system within composites is limited by the poor thermal conductivity and high thermal sensitivity of polymeric materials. Many studies have reported uses of conductive polymers, metals, CNT and carbon black to make conductive polymer composites; however, they still suffer from poor thermal and electrical conductivity, and higher energy consumption. Therefore, it is desirable to use a conductive material that can provide excellent electro-thermal properties as well as can achieve desired temperature without compromising existing mechanical and thermal properties of composites.
CSIRO has created a new form of graphitic material that’s conductive, easy to apply and offers greater control over performance than graphene. GraphON can also be manufactured cheaper and easier, with more flexibility and less hazardous waste than comparable products.
The materials can be used in applications in electrical heating (de-icing) for aerospace applications. It can be mixed into polymers or paints to create a surface coating that conducts heat or electricity. GraphON can be manufactured with flow chemistry, guaranteeing a product that’s safe, efficient, cost-effective and consistent.
SAAB has filed a patent for the development of de-icing coatings. The graphene additive could strengthen the acrylics and shield against EMI interference.28 Lockheed Martin is working with Rice University on graphene de-icing coatings.29
Companies
Adaptive Surface Technologies, Inc.
USA
Adaptive Surface Technologies (formerly SLIPS Technologies) is a spin-out from Harvard University. The company launched in October 2014 with a $3 million Series A financing led by BASF Venture Capital. SLIPS (Slippery Liquid-Infused Porous Surfaces) changes the surface of a solid material into a microscopically thin and ultra-smooth (friction-free) immobilized “sea” of lubricant.
SLIPS creates a stable and immobilized liquid lubricant overlayer (LOL) and this “liquid surface” provides extremely slippery (low contact angle hysteresis) and non-sticky surfaces against a wide range of viscous contaminants, biofouling, ice and frost.
Alchemy Nano
Canada
https://alchemynano.com/
Alchemy is a spin-out from the University of Waterloo.
The company’s Exoshield films use multi-layer nano composites to protect a vehicle’s windows and windshields from natural and seasonal elements, such as insulating against summer heat, preventing frost during winters, and avoiding stone chips. It caters to autonomous vehicles, windshield protection, and defense and security applications.
The company’s products are available through a global network of distributors. Alchemy was formerly known as Neverfrost, Inc.
AF220 Anti-frost nanocoating is designed to prevent formation of overnight frost on any desired substrate such as glass or polycarbonate for automotive applications. The coatings enable multi-climate reliability for AVs by providing impact/scratch resistance, frost prevention, de-icing to combat snow/freezing rain, and water/dirt shedding. It is an easily applicable, transparent, infrared-reflective and anti-frost film.
Agiltron, Inc.
USA
www.agiltron.com
Agiltron has developed robust and affordable anti-icing and ice-phobic surfaces that are also transparent (>%80) in visible spectrum for superstructures of surface ships in Arctic and cold region operation. Leveraging Agiltron”s previous experiences in mechanically durable superhydrophibic nanocomposite coatings and optically transparent fluoropolymer resins, in collaboration with the Ice Research Laboratory at Dartmouth College, they have produced nanotextured superhydrophobic nanocomposite coatings of hard nanoparticles embedded into a fluorinated polyurethane resin matrix, both are optically transparent in the visible spectrum. This nanocomposite coating is highly transparent, easy to apply via spray coating over large areas and containing no volatile organic compounds.
Battelle Memorial Institute, Inc.
USA
www.battelle.org
The company produces the HeatCoatTM ice protection technology that utilizes a carbon nanotube coating that can be sprayed onto an aircraft.
Figure 4: Carbon nanotube de-icing coating.
Image: Battelle Memorial Institute, Inc.
Helicity Technologies, Inc.
USA
www.helicitytech.com
IceShield coating formulations are UV weathering and corrosion resistant, environmentally friendly, and feature extremely low ice adhesion strength (shear stress averaging less than 0.04 MPa at -20° C). They can be easily applied across very large or irregular surface areas using conventional spray coating and painting methods.
For applications that require optical clarity, Helicity offers a transparent formulation that can be sprayed onto virtually any surface, requires no curing, and lasts over 30 icing/de-icing cycles. For industrial applications requiring rain-erosion resistance and durability, Helicity offers an opaque, two-component coating with anti-icing properties that can last for approximately one year.
Any ice, snow, or frost that accumulates on treated surfaces can be easily wiped away, thus reducing or eliminating the need for thermal, mechanical, or chemical de-icing methods.
Phazebreak Coatings LLC
USA
http://phazebreak.com
Phazebreak Coatings has developed a Patented Icephobic Transparent Coating, NEINICE, that minimizes ice accumulation and provides protection. The coating contains novel silicone-based phase change materials (PCMs).
SurfEllent, Inc.
USA
https://surfellent.com/
SurfEllent produces anti-icing coatings from various polymers with extremely low ice adhesion and good durability under severe environmental conditions. The product is either applied via paint or spray.
Synavax
USA
www.synavax.com
Energy Protect™ and Hydrophobic coatings are utilized for ice prevention. Energy Protect™ coating applied to bridge soffits and tunnel structures provides resistance to icicle formation, thus reducing the cost for icicle removal and increasing rail safety
X-Therma Inc.
USA
X-Therma Inc. is a biomimetic nanotech company with the mission to develop safe & effective antifreeze solutions to enable long term bio-banking of Regenerative Medicine and enhance mechanical performance at extreme temperatures for greener industrial applications. The company has developed a bioinspired, non-toxic and anti-ice nanomaterial via biomimetic nanoscience.
References
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18. http://adsabs.harvard.edu/abs/2014JMiMi..24i5020W
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29.http://news.rice.edu/2013/12/13/graphene-nanoribbons-an-ice-melting-coat-for-radar/
Further information
The Global Market for Ice-Resistant Coatings and Surfaces
Published April 2019
