Interaction

Starting with this issue of A10, Els Zijlstra, director of Materia, will bring us up to speed on the latest materials. This first article is devoted to interactivity. It is a plea for a new approach to materials, based not purely on their technical properties but first and foremost on their effects.

Materia’s view on ‘communicating’ materials

We are seeing more and more of them around us: buildings that change colour by means of lighting, facades and walls sporting texts, photographs and illustratio coatings that change colour, LED lighting embedded in glass, luminous tiles. These new inventions enable architecture to ‘communicate’ by actively responding to the observer, the user, the weather, the traffic or the environment in general. This is no passing fad, but a lasting enrichment of architecture that requires a whole new vocabulary.

Some fifty years ago, architects had at most twenty materials to choose from; today they have an exhaustive arsenal at their disposal. Not only has the choice of materials become more difficult, but many of these new materials have a range of possible uses. In short, the meaning of materials in architecture has changed and we need new words and terms to express those meanings, terms that go beyond a dry enumeration of their technical properties and describe how materials – especially interactive materials – appear to us.Genuine interaction occurs when a building, or at any rate the facade, is able to react to impulses it receives from the environment. There are many ways in which this can happen and thus many design possibilities. Sensors pick up stimuli which a processor then translates into commands that cause the building to react. The sensors register variations, for example in weather conditions or the presence of people. Practical examples are sunlight sensors that activate solar shading and rain sensors that automatically operate a car’s window wipers or the windows of a house. But it’s not difficult to imagine other possibilities that would enable a building to speak or to provide information or that would enhance its architectural statement.Translucent materials are by their very nature interactive. The incidence of light, the difference between inside and outside, means that such materials can be experienced in different ways. The fascinating thing about translucency is that it raises the question of the immateriality of the material: at the point of maximum transparency you are not aware of any material. In his thesis ‘materialeimmateriale’, architect Marco Sardella described the perception of transparent and translucent materials. He was interested not so much in the scientific properties of these materials as in their effects, their contribution to the experience of architecture, their capacity to reveal, indicate, reflect, disperse or disorientate.

Terminology
These meanings have not yet been precisely defined, but they are a starting point and an invitation to capture the ex-perience of new materials in a new terminology, so that alongside the technical and aesthetic descriptions of mater-ials there is also an architectural description using a vocabulary based on perception. In the rapidly growing jungle of mater-ials such a vocabulary is sorely needed if we are to continue understanding one another in the future:

Reveal
Whether an object appears in the foreground or merges with its surroundings depends on the degree of translucency of the material. The relevant materials allow direct or diffuse light transmission, or both – as in the case of Lumisty (a glazing film), where the background is by turn clearly outlined, ill-defined, diffuse or ‘misty’, depending on the angle of incidence.

Indicate
The material changes its appearance and so ‘communicates’ with the viewer. This property is often associated with attributes like luminescence, as in materials that light up or fluoresce.

Reflect
Reflection results in the projection of a virtual image or the multiplication of a real object. This mirroring effect can take several forms: with clear or vague outlines, as a multiple image, as a distorted, deformed image or as a diffuse shadow. Combinations of reflection and translucency can be achieved with metallic surfaces, dichroic filters, Optical Light Film and coloured glass.

Disperse
A material with this capacity reveals its three-dimensional structure when light strikes it in a particular way. Examples are materials laminated with translucent materials, like Cristal de Ravier and Texluce, which reveal the thickness of the material, but also perforated sheets, foams and three-dimensionally woven materials like Parabeam.

Disorientate
A disorientating material behaves differently from what its material properties would lead one to expect. It elicits surprise; unable to determine what it is, the viewer can at best ascertain what it does. Examples are materials that change colour in response to UV radiation or temperature fluctuations, holographic materials, and so-called flip-flop materials that change colour when viewed from a different angle.

Material characteristics
Effects like these can be achieved with different techniques such as dichroic filters, flip-flops and smart materials.

Dichroism
A dichroic filter (film or glass) is made up of several thin layers. Light rays are reflected by each of those thin layers and, as it were, flung back and forth by the filter. The colour light with a wavelength exactly the same as the thickness of the layer will be strengthened and be able to penetrate the filter. The rest will be extinguished. As with iridescent surfaces, the colour of the surface shifts according to changes in the incidence of light and the position of the viewer.

Flip-flop
An iridescent surface has a structure which causes light rays to split into multiple rays with different wavelengths and colours. As the light shining on it changes colour, so too does the surface of the material. This effect occurs frequently in nature – think of fish scales, beetle cases and a peacock’s tail feathers. The greatest effect is produced by movement and iridescent paints come into their own on moving objects (as Alfa Romeo showed with their mother-of-pearl colour range), or in situations where the observer is moving (facades, advertising). Just as the effect is often used in nature to mislead enemies and rivals, so in architecture it serves to confuse and surprise, and to add an extra dynamic to the surface.
The flip-flop effect is also familiar from credit cards – a prismatic surface is printed with superfine coloured lines which present a different image depending on the viewing angle. For the same reason, prismatic LENZ acrylic sheets developed by Bernd van der Stouw lend themselves to facades and interiors – the images printed on them change as the observer moves.

Smart materials
These are materials that undergo big changes in shape in response to external influences such as stress, temperature, moisture, acidity (pH), electrical or magnetic fields. The material may react with a shift in colour, in transparency, in volume and/or rigidity. Just as our brains are linked to sensors and muscles, so the smart material has a processor, an acceptor and a reactor. The acceptor detects a change in conditions and relays this to the processor which registers the level and quantity and passes this to the reactor which initiates the visual reaction. Depending on the type of smart material concerned, the process may or may not be reversible.
The ‘piezoelectric effect’ describes the ability of crystals to generate a voltage in response to applied mechanical stress (such as bending). The effect is reversible: crystals can deform when subjected to an externally applied electrical voltage.
Shape Memory Alloy, or SMA, is a material that is able to return to its original geometry after deformation if it is heated. At higher temperatures this effect can also occur when the stress is removed. What happens is that the material, which after deformation finds itself in the martensite phase, gradually returns to the austenite phase, a transition from one molecular structure to another. The most commonly used shape memory alloys are nickel-titanium (NiTi) and copper-zinc-aluminium (CuZnAl).
Photochromatic materials can change colour in response to light. This process is reversible. Normally, such materials are colourless in the dark. As soon as sunlight or ultraviolet light falls on them, their structure changes resulting in a colour shift. When the light source is removed, the material returns to its original colour. Changes from one particular colour to another are achieved by combining photochromatic mater-ials with prime colours.
Thermochromatic materials change colour reversibly in response to changes in temperature. They can be made as a semi-conductor, from crystals or metals. The temperature at which the colour shift occurs can be altered by adding more adjective dyes. Their applications are the same as for photochromatic materials.
Light-emitting materials also exist in the form of electroluminescent, fluorescent and phosphorescent materials.