When a droplet of water lands on the lotus leaf, it beads up, rolls off the leaf surface without leaving a trace of water behind and washes away any dirt along its way. This self-cleaning property fascinated scientists for a long time until recently, when scientists realized that this peculiar behaviour is due to the nanostructures present on the surface of the lotus leaf. They term this as super-hydrophobicity.
Surfaces with our coatings behave like the lotus leaf and stay dry when water land on them. Such degree of water repellency exceeds even that of one of the most well-known hydrophobic materials, polytetrafluoroethylene (PTFE) or Teflon. Hypho Technology is developing a method to impart these nanostructures on surfaces. Finally, with our unique formulation, the nanostructures can be sprayed onto most surfaces to make them super-hydrophobic for the first time. Another unique quality of our formulation is that it is water-based which means that there is no volatile organic compound (VOC) and poses no health hazard to the users. Hypho Technology pledges to conserve water to help save the environment.
In 1964, Dettre and Johnson studied the Lotus effect phenomenon for its high water repellency property. Other natural objects similarly studied included cane and certain inserts' wings. Lotus is a native plant in Asia and its self-cleaning property has been known for more than 2000 years. Dirts on the Lotus leaf can be easily picked up by running water droplets and eventually be removed from the leaf.
With introduction of the scanning electron microscope in the early 1970s, a german botanist Wilhelm Barthlott was able to peek beyond the magnification of an optical microscope and look at the micro scale of the lotus leaf topography. Today, we know very well that the nano scale feature of the leaf play an important role too. Today, superhydrophobic coating has been using in biomimetic devices, and in chemical and biological fluids.
Hydrophocity are frequently measured with water contact angle with respect to the substrate. Contact angles greater than 90 degree are considered as hydrophobic. The theoretical maximum contact angle for water on a smooth surface is 120 degree. Micro- and nano-structured can exhibit contact angles exceeding 150 degree and are considered superhydrophobic and the lotus leaf effect. Under gravity, the water droplets can roll off and the surface remains dry.
In the contact angle measurement, small drop of water is slowly squeezed off and the angle angle will vary with increasing volume of water. When the volume is increasing, it is called the advancing angle. When the volume is increasing, it is called the receding angle. The angle difference is denoted as the contact angle hysteresis which gives a degree of the surface stickiness. The greater the hysteresis the more water drops will adhere to the surface. A superhydrophobic surfaces will give a low hysteresis angle. In addition, a small hysteresis means water droplets will roll off the surface easily.
Water is the most abundant molecule on earth's surface. Water is the only common compound found naturally in all three liquid, solid, and gaseous states. Water is a polar molecule: The water molecule forms at an angle making up of hydrogen atoms on one side and oxygen at the opposite vertex. Due to the polarity nature, water has high cohesion and adhesion properties. On a clean and smooth surface, the water wets and spreads to form a thin film. This happens when the adhesive forces are stronger than the cohesive forces. Hence surface plays a important role of water wetting behavior. Another property to consider is the surface tension of water droplets. Water droplet reduces their surface to volume ratio so as to minimize surface energy. In so doing, the water droplets often adopts a spherical shape or dewetting. When the area of contact between the water droplets and the surface is smaller, the droplets will roll under gravity or simply be blown away by wind. This constitutes the self-cleaning behavior of the surface mediated superhydrophobic phenomenon.
Over the years, scientists have found mechanisms of the lotus leaf’s self-cleaning properties. It is the special waxy composition coupled with topographic features of micro-scale bumps and nano-scale hairs on the leaf's surface. Wenzel and Cassie-Baxter theories on hydrophobicity research have pointed out that a rough surface is essential to enhance hydrophobicity. In a research finding, a rough waxy surface can improve the contact angle by 16 degrees over a smooth waxy surface. In their theoretical development, water can either penetrate the pores (Wenzel) or suspend above the pores (Cassie-Baxter). In both cases, much higher apparent contact angle can be observed that a smooth surface.
Hypho Technology combines nanotechnology and chemical treatment to produce super-hydrophobic coating solution for water repellent applictaion. A cost effective sprayable solution design for glass, metal and ceramic surfaces. Hypho Technology's coating (insert: left is treated, right is untreated) is translucent and have large contact angle for easy water droplets rolling. It has been tested for outdoor durability and able to withstand outdoor conditions.
Applications of Hypho Technology's Superhydrophobic Coating
A coating on the urinal eliminates the need for flushing. Urine rolls down easily to the drain or bio-clean cartridge without sticking on the wall.
Household items such as clothings, bags, shoes and hats are desirable to be waterproofing. Coating will repel water away but allow air to pass through.
Water will roll off the treated surface together with any dust and dirt. Ideal for windows and rooftops.
Wet wall promotes the growth of bateria, mold or stain. Water-repellent wall prevent water from wetting it.
Especially useful for automobiles. Water dewet on car surface. After drying, these water beads will leave behind water marks or stain. Water repelent coating remove water beads in the first place.
Windscreen coated with transparent superhydrophobic coating can eliminate the need for screen wipers. On light rainy days, water drops are easily rolled off from the windscreen on the move.
Water drops on the toilet walls and shower screen can leave behind water stains upon drying. Water-repellent coating keeps them dry and stain free.
Self-cleaning property on solar panels can remove dirt and dust on rainy days. Thus it reduces the need for frequent maintenace to keep the solar panel's surface clean. A cleaner surface helps the solar cell to operate at optimum efficiency.
A water-repellent coating on ferro metals prevent corrosion due to rain and humidity.
A water-repellent coating remove water off the surface and there will not be freezing problem. This is useful for aerospace industries or building where freezing water induce mechanical weakening to the structures.