Frequently asked questions
- What are self-cleaning surfaces?
There are basically two types of self-cleaning surfaces. In the first place we have extremely water repellent, microscopically rough surfaces: dirt particles can hardly get a hold on them and are, therefore, removed by rain or by a simple rinse in water. The second example is given by photo-catalytic layers: due to a layer of titanium oxide, fouling organic material is destroyed by solar irradiation.
“Self-cleaning” and “easy-to-clean” surfaces are frequently confused and, in advertisement, mixed up intentionally. Easy-to-clean surfaces are widely distributed. They are entirely unrelated to Lotus-Effect® surfaces. The latter do not need to and, indeed, should not be wiped over in any way with a cloth.
- What does the term Lotus-Effect® stand for?
- The self-cleaning of super-hydrophobic micro-to nano-structured surfaces was observed to be a property of some plants –among them nasturtiums (Tropaeolum sp.)- in 1975. The discoverer, Wilhelm Barthlott (then at the University of Heidelberg), furthermore, elucidated the phenomenon. Only at the beginning of the 1990s was it possible for W. Barthlott (now at the University of Bonn), and his collaborator Christoph Neinhuis (later Zdenek Cerman and others) to harness this physico-chemical phenomenon technically. W. Barthlott coined the trade-name Lotus-Effect® for the patented self-cleaning super-hydrophobic micro –to nano-structured products and copyrighted it in 1997.
- What are self-cleaning super-hydrophobic micro to nano-structured surfaces?
- During millions of years of evolution nature has developed surfaces – the ideal example are leaves of the Lotus (Nelumbo nucifera) - which, through a complicated micro- to nano surface structure, repel dirt. We discovered this in the mid-1970s and applied it in the mid-1990s to technical products. Concerned are surfaces that, due to their chemistry are water repellent (hydrophobic). Determining for the particular properties, however, is not only the chemistry but, in particular, the micro- to nano structure: in the ideal case this is composed of a bulky structure (5-10µm in diameter) and a fine structure (10nm to 5µm) layered on top. The adhesion of particles to these surfaces is minimal because they touch, like a fakir on his bed of nails, only the tips of the structure. They are washed away by water droplets, which roll off. The technical conversion is patented; in the mid-1990s the trade name under copyright: Lotus-Effect® was introduced for the commercial products.
- Which Lotus-Effect® products do already exist?
Lotusan® , an exterior paint from the firm Sto is marketed already with the greatest success since 1999. It is used by professional firms of house painters and is, not yet, available for the general building trade. Up to the present Lotusan® has been used to paint c. 300,000 buildings. In 2004 Degussa (daughter company of Goldschmidt) has introduced the first spray: Tegotop® 105 which can be used to impregnate surfaces. Self-cleaning textiles are being tested at present and will be available commercially from summer 2005. Marquees will probably the first to receive such treatment. Optical sensors in public high impact areas (for instance toll bridge sensors on highways) are furnished already throughout Germany with Lotus-Effect® glass manufactured by Ferro AG. A series of further products is being tested, among these Aeroxide® LE of the Degussa for plastics.
As a customer one is frequently wrongly informed by advertisement. There exist, for instance, a large number of exterior paints that claim to be Lotus-Effect® products. Of these, Lotusan is the single paint with such characteristics. On the open market there are still items (e.g. frying pans), also a large firm producing sanitary ceramics, an important manufacturer of floor coverings, two textile firms and on bespoke spectacle producer – they all claim to trade in Lotus-Effect® products. All these makes have no connection with the trade name Lotus-Effect® and are not covered by patented self-cleaning micro- to nano structured surfaces.
- Patents and trade names
- The transformation of nature’s pattern into technical self-cleaning super-hydrophobic micro- to nano structured surfaces is patented. The European patent was granted in 1998. Outside Europe a patent protection exists in most countries (the U.S.A. among others. As a marketing term for super- hydrophobic micro-to nano structured surfaces W. Barthlott coined the trade name Lotus-Effect® in the mid-1990s and registered it in 1998 as a trade name. A further patent for the manufacture of temporary, detachable self-cleaning surfaces, “sprays” was granted in 2003. In the meanwhile altogether in excess of 100 dependent patents exist which are held, to a large extent, by our collaborators in the project Lotus Effect®.
- Where is it impractical to employ Lotus Effect® products?
Our self-cleaning surfaces need running water for cleansing. The use of Lotus-Effect® products in some interiors, for instance on wallpaper or furniture is, therefore, not very sensible. Lotus-Effect® surfaces are without mirror effect and slightly matt. They function on architectural glass (Ferro), but hardly on optical glass or even spectacles.
A number of spectacle manufacturers, among these a brand leader of renown, offer, in spite of this, products that, allegedly, have the Lotus-Effect®. This, however, rather amounts to misleading customers. Lotus-Effect® products always have a micro-to nano-structured surface. It is, therefore, not possible to expose Lotus-Effect® products to extreme mechanical stress. Thus floors, slide rails or similar objects are, at present, not yet areas of application for the Lotus-Effect®. Interestingly, there exist already the first prototypes of Lotus-Effect® products that can be exposed to extreme mechanical conditions. Unfortunately the Lotus-Effect® offers no anti-graffiti protection.
- How durable are Lotus Effect® products?
- House fronts that had been painted with the commercial product Lotusan® are, after now more than 5 years, unchangeably self-cleaning. Everything points to these products having a very long durability. Dependent on the application it can also make sense to create temporary self-cleaning micro-to nano structured surfaces. This can be accomplished, for instance, with the spray Tegotop® 105 from Degussa, which enables a temporarily limited impregnation of, say, garden furniture or of cars for the duration of winter.
- Are Lotus-Effect® sanitary ceramics and shower cabins available?
Wetting agents (e.g. soap, washing up solutions) interfere with the droplet formation of water. With Lotus-Effect® too some wetting occurs. Of course, the surface is not destroyed by the wetting agents, rather, after rinsing with clean water, it is again fully able to function. This fact means, of course, that products with Lotus-Effect® have no application in areas of sanitary work were whetting agents are used intensively (e.g. sinks), using them here hardly makes any sense; similar considerations apply for organic solvents.
A very well known manufacturer of sanitary ceramics persuasively includes in his advertisement pictures of Lotus flowers and suggests to the customer that the surfaces would work according to nature’s pattern. These surfaces are basic easy-to clean surfaces and have nothing to do with the Lotus-Effect®.
- Do Lotus-Effect® glasses and spectacles exist?
For years self-cleaning glasses have figured in advertisement. Frequently this is about so-called photo catalytic stratificatio. The firm Ferro keeps prototypes of architectural glass with Lotus-Effect® in permanent test conditions. In the region of optical sensors (toll bridges) Lotus-Effect® glasses are already used successfully. For architectural glass and rear windows of cars applications will probably follow soon. For optical glasses and spectacles the Lotus-Effect® is hardly suitable.
Many glass manufacturers and producers of some such “miracle substances” for the impregnation of glasses pretend to trade in Lotus-Effect® products. Unfortunately this is even true for spectacles for which a brand manufacturer of renown advertises pretending to trade in Lotus-Effect®.
- Do self-cleaning roof tiles and roofs exist already?
- Yes, with Erlus-Lotus® the first self-cleaning roof in the world came on the market.
- Are Lotus-Effect® stratified anti-fouling layers for ships and boats available?
- No. Self-cleaning super hydrophobic micro-to nano structured surfaces with the trade name Lotus-Effect® include a 3-phase interaction between object, air and water. Permanent under water, there can be no self-cleaning according to the Lotus principle. Consequently the application on hulls of ships, in pipelines, drainage systems or in heart catheters is misplaced.
- Where is the Lotus-Effect® spoon available for sale?
- For demonstrations we employ a spoon with a perfect Lotus-Effect® surface. Honey and many other substances roll off without a hint of residue. The spoon is a prototype that is, unfortunately, not for sale.
- Are there sprays that bring about Lotus-Effect® surfaces?
- At the moment not yet available on the open market. However, firms can already order the first spray Tegotop® 105 for testing from the Degussa-Goldschmidt AG. It can be expected that from summer 2005 sprays will be commercially available for the private consumer.
- Do self-cleaning plastics and foils exist?
- Many prototypes are being tested. The exclusive licences for polymeric super-hydrophobic micro-to nano structured foils and parts of plastic are held by the firm Degussa. Here the permutation is being researched intensively. One product for the industrial transformation (Aeroxide® Le 1, Le2, Le3) has already reached the market place.
- Do we have textiles with Lotus-Effect®?
A great number of prototypes exist already. It is envisaged, however, that the first products will reach the market only in the summer of 2005. The properties of the new-fangled intelligent textiles are astonishing. Not only does water roll off, but ketchup and red wine do likewise. The area of use will hardly lie with suits, ties or shirts, but rather with outdoor clothing, marquees, tents and with tarpauling for lorries. In the area of “textile building” a new dimension will open up.
Two large firms producing textiles advertise since 2004 with products that are not related in any way to our patented, self-cleaning super-hydrophobic micro-to nano structured. surfaces. Illegally even the name Lotus-Effect® is being used.
- Lotus or Lotos: Which is the correct name of the plant?
The Lotus-Effect® has been named for Nelumbo nucifera, the water plant with the shield-shaped leaves and the wonderful flowers. In English and French as well as in most other languages, Nelumbo nucifera is called Lotus, in German mostly Lotos. We have adopted the generally accepted international spelling and refer to the Lotus-Effect®.
Great confusion reigns concerning the spelling and the content implied by that name. Our Lotus flower has been described already in earlier days under the name Nelumbium lotus. In antiquity Lotus and Lotos were used to name the most diverse plants. The true Lotus flower was, in fact, at home in the Nile delta and in the area of the eastern Mediterranean and is mentioned several times for this region. Presumably it became extinct here around 1000 B.C. At the same time it is confused already from antiquity with the Egyptian Lotus flower (Nymphaea lotus) which is, in reality, a water-lily (in this context compare F. Woenig, Die Pflanzen im alten Ägypten (The plants of ancient Egypt), Leipzig 1897). To complete the confusion: the birds-foot trefoil (a papillionid with many species) has the generic name Lotus and, more, a small tree of the buck thorn family growing in the Mediterranean region bears the name Ziziphus lotus. In other words, this is a perplexing name with diverse spellings. Bernard Herzhoff is right when he states in his essay that Lotus is one of the most confusing plant names ever. Entitled: “Lotos – botanical observations on a homeric plant name” (HERMES, Zeitschrift für klassische Philologie (Journal for classical philology) 112: 257-271, Stuttgart 1984).
The literature on this problem fills many 100 pages and a final solution is not in sight. We follow the international usage of language and name Nelumbo nucifera the Lotus flower, the natural pattern for the Lotus-Effect®.
- Can Lotus be cultivated in the garden?
- Yes. In the tropics and subtropics Lotus can be cultivated easily. But also in regions with cold winters like Germany the cultivation in the garden is possible. Detailed information on this topic is available on the homepage of the Botanic Gardens Bonn and in the issue 6/2005 of the garden magazine „Gartenpraxis“.