FACTOR FOUR - lotus-effect

Dirt-repellent surfaces with lotus effect
Using nature as a model
Dirt-repellent surfaces save work and cleaning agents.
Nature provides the model. Many plants have water-repellent leaves, and the lotus or sacred water lily is a prime example. Water runs off its surface in little beads. Biologists at Bonn University discovered that these surfaces not only repel water, but also dirt as water running off the surface takes dirt with it. A look through the microscope reveals that the leaves’ rough surface offers water no hold.
Nano-technology allows applying extremely fine microstructured finishes to materials that imitate the surface of lotus leaves. So far, the lotus effect may be found in house paint, tiles, glass panes and plastic sheets. Roof tiles with lotus effect are at the development stage.
Easy-to-clean surfaces in sanitary ceramics and flooring have qualities similar to the lotus effect. Since these surfaces do not feature an actual lotus effect, they cannot be called self-cleaning, but nevertheless offer comparable advantages.

Self-cleaning facade painted with Lotusan
(Source: Department of Botany at Bonn University)

Manufacturers and suppliers

Factor-four effects

Ecological effects

Resource use
Dirt-repellent surfaces save cleaning agents and water. They make facades and floors more durable, reduce the need for repairs and replacement, and in the end save material.
Durability
House facades remain drier and last longer even on the side exposed to the weather. Flooring is dirt-repellent and scratch-resistant and has a longer lifespan. Finishes for sanitary ceramics are chemically and thermally stable and scratch-resistant. Lotus finishes do not rub off.
Waste
Long-lived, easy-to-clean products cause less waste.

Economic effects

Cost-effective in maintenance and care
Lotus-effect facades are drier and keep micro-organisms like fungi and algae at bay. Moisture-resistant facades require less frequent painting or other maintenance work. Easy-to-clean flooring saves costs because it is easier and quicker to clean and needs less frequent refurbishment. Slightly higher up-front costs for easy-to-clean sanitary ceramics are amply balanced by savings in care throughout the product's lifespan.

Social effects

Quality of life and saved time
Cleaning is less time-consuming.
Attractive surfaces and positive image
Surfaces stay clean and attractive, facades age better. The visible advantages of lotus or easy-to-clean products immediately meet the eye; their attractive look will find many followers.
Safety
Lotus vehicle windshields increase road safety as the water- and dirt-repellent surfaces improve visibility and allow quicker reaction to road hazards.
Biomimicry/bionics
Lotus products show that nature serves even technology-dominated fields as a model.

Obstacles and drawbacks
Not observing care instructions, e.g. using aggressive cleaning agents, may impair these surfaces' unique properties. Poor workmanship in handling or applying the product can destroy the effect, and not all surfaces respond to treatment. The same goes for easy-to-clean-surfaces.
In nature, lotus leaves and leaves with similar characteristics last only one season, and one difficulty lies in making artificial lotus products durable. Coatings and finishes were launched only recently, so no sufficient data exist to prove their durability.
The lotus effect in house paint is disputed. Its dirt-repellent characteristics seem to base on the water-repellent characteristics of silicone paint as such, a product that independent of any lotus effect has been on the market for some time. House paint has not fulfilled all expectations so far. A "self-cleaning" effect requires certain favourable conditions (i.e. façade exposed to rain). Rain water has to run off evenly to prevent ugly dirt streaks e.g. below window sills.
In the long term, fine dust particles can lodge in the surfaces of lotus tiles. The lotus surface then effectively prevents cleaning because it repels water with cleaning agents. The result is an irremovable grey film. Research now focuses on developing suitable cleaning agents.
Lotus-effect vehicle paint is possible, but its matt polish fails to attract customers.

Potential
There is great potential in microstructured surfaces.
A wide variety of surfaces can be treated with the lotus effect or other water- and grease-repellent coatings to keep them clean. The range of possibilities extends from glass roofs to clothes and road signs. Interesting new developments may be expected in the field of temporary lotus-effect coatings designed for limited durability.

Expert advice

For questions on lotus-effect please contact:
Dipl. Biol. Zdenek Cerman
Department of Botany at Bonn University
Meckenheimer Allee 170
53115 Bonn
Tel. +49-(0)228-73-2122
Fax +49-(0)228-73-3120
cerman@uni-bonn.de

Workinggroup "lotus-effect"
Tel. +49-(0)228-73-1919
lotus@uni-bonn.de

For questions on FACTOR FOUR please contact:
Dr. Raimund Bleischwitz
Tel. +49-(0)202-2492-256
raimund.bleischwitz@wupperinst.org