During the last ten years of the century significant changes have taken place in materials science. The ever-increasing user requirements have resulted in a change of paradigm.

Ability to adapt to the environment has become the key word of the new way of thinking.

The endeavour to make materials passive and unchanging has been replaced by an approach that examines the dynamic coexistence of the material and its environment. A new concept has appeared, which was called intelligent material. The main aim is the design and production of artificial materials which through their active interaction with the environment they change their characteristics favourably for the user.

We call those multi-functional materials intelligent materials that directly sense one or more features of the physical or chemical state of their immediate environment, process the information deriving from these, then give a fast and clear answer to this by significantly changing their state.

Most frequently the sensing function can be realised as a result of the balance between the material in question and the environment. This balance may be chemical, mechanical or thermodynamic. The change in the environmental parameters necessarily brings about a change in the balance state. And in the newly formed balance state the material has different characteristics. A further important aspect is the connection between the effect bringing about the change, henceforward stimulus and the reaction happening because of this henceforward answer. Non-linear stimulus-answer connections are characteristic of intelligent materials in which for a small change in the environmental effect a very large change in characteristics takes place, in other words the degree of answer is not in proportion with the size of the stimulus, but very much greater. A further criterion is reversibility; that is after the effect causing the change has ceased the original state has to return. A fast reaction time is an application technology requirement.

The subject of the invention is the multi-layered glass so called intelligent glass. This is a sandwich structure which, between two glass sheets or transparent plastic layers, contains a thin polymer system. Its external appearance form is deceptively similar to sheet glass that is in commercial distribution, in other words the polymer system does not degrade the optical characteristics. The adapting ability of the intelligent glass is provided by the polymer layer.

Its optical characteristics-for example transparency-are greatly influence by environmental effects like for example temperature change or the presence of an electric field. The change in the environment may bring about changes in the intelligent glass that cause the originally transparent glass to become opal glass, cloudy, only allowing light through to a much smaller degree. This transparent glass-opal glass transition can take place in both directions.

In one of the types of intelligent glass developed by us a change in the temperature of the environment brings about the glass-opal glass transition. With the appropriate composition it can be achieved that sun radiation causes this transition. A window made from intelligent glass provides a comfortable solution for protection against strong, direct sun radiation.

In another type of intelligent glass the glass-opal glass transition can be brought about by ourselves by switching on an electric circuit. With this, for example, the transparency or opacity of internal windows can be controlled with the switching on or off of a switch.

Intelligent glass is suitable for making a new type of display. It is possible to write letters of the required size in the polymer, or a drawing. These may be called up and made to disappear with a thermal of electrical effect.

Intelligent glass changes its optical characteristics due to a thermal or electrical effect suddenly-not gradually-in a way that may be reversed. The layer between the layers of glass is responsible for this change. This layer may be of a cross-linked or non-cross-linked homopolymer, co-polymer, polymer solution, polymer gel or a mixture containing polymer, solvent (solvents) and other small molecule components which have lower or upper (or both) plait point temperatures, or other transformation temperatures that affect optical characteristics (like, for example, the Kraft point or the clouding point).

How the intelligent glass changes its optical characteristics depends on the layer's phase characteristics. In the case of a lower plait point an increase in the temperature brings about the glass-opal glass transition. The opposite of this takes place in the case of an upper plait point.

The value of the temperature of electric parameters bringing about the glass-opal glass transition may be changed between a wide range by changing the chemical structure of the layer and the additive materials put in the layer.

In specialist literature and general knowledge types of glass are known that change their optical characteristics due to thermal and/or electric effects. One type of such is the so- called phototropic glass. When visible light is radiated on this its light transmission ability gradually decreases, which process is reversible. In phototropic glass the linking of two significantly different phenomena results in the non-sudden change of the optical characteristics.

The operation of the other known type of glass is ensured by the structural transformation of liquid crystals.

The multi-layered glass structure that forms the subject of our invention is different from the above-mentioned types of glass both from the points of view of its chemical structure and operating method. At the same time its much cheaper material and production cost and the sudden changing of its optical characteristics creates the conditions for its wider area of application. To the best of our knowledge the application of gels to produce glass with regulatable light permeability is not known in the specialist literature.

Without restricting the protection request we illustrate the procedure for the production of intelligent glass with the following examples: Example 1 Glass-opal glass transition brought about by temperature increase Starting materials: polyvinyl alcohol (PVA), Glutaraldehyde (GDA), 25 v% water solution, HCI 37 m% water solution, Lutidine, To a 100 cm3 8 m% PVA solution we add 40 cm3 20 v% lutidine-water mixture. After mixing the two solutions we add 0.4 cl3 1 M GDA solution. For the gelation we set the pH of the solution to a value of 2 with the water HCI solution. The solution is poured in a 0.5- 1 mm gap between the pre-prepared two well sealing, flat glass sheets. After the gelation has completely taken place (approx. 5-8 hours) the intelligent glass may be used.

Example 2 Glass-opal glass transition brought about by temperature reduction Starting materials: polyvinyl alcohol (PVA) Glutaraldehyde (GDA), 25 v% water solution, Iso-butyric acid To a 100 cm3 8 m% PVA solution we add 40 cm3 15 v% iso-butyric acid-water mixture.

After mixing the two solutions we add 0.4 cl3 1 M GDA solution. The solution is poured in a 0.5-1 mm gap between the pre-prepared two well sealing, flat glass sheets. After the gelation has completely taken place (approx. 1-2 hours) the intelligent glass may be used.

Example 3 Glass-opal glass transition brought about by temperature reduction Starting materials: polyvinyl alcohol (PVA) Glutaraldehyde (GDA), 25 v% water solution, HCl 37 m% water solution Polyethylene-polypropylene block co-polymer (PEPP) To a 100 cm3 8 m% PVA solution we add 40 cm3 8 m% water PEPP solution. After mixing the two solutions we add 0.4 cm3 1 M GDA solution. For the gelation we set the pH of the solution to a value of 2 with the water HCl solution. The solution is poured in a 0.5-1 mm gap between the pre-prepared two well sealing, flat glass sheets. After the gelation has completely taken place (approx. 5-8 hours) the intelligent glass may be used.

Example 4 Glass-opal glass transition brought about by temperature increase Starting materials: n-iso propyl-acryl-amide (NIPA), N, N'-methylene-bisacrylamide (MBA), Ammonium-persulphate (APS), N, N, N', N'-tetramethylene-diamine (TEMED) In a 100 cm3 water solution we dissolve 15 g NIPA and 0.133 g MBA. To this we add 80 mg APS and mix 200 ul TEMED solution. The solution is poured in a 0.5-1 mm gap between the pre-prepared two well sealing, flat glass sheets. After the gelation has completely taken place (approx. 5-8 hours) the intelligent glass may be used.

Example 5 Glass-opal glass transition brought about by temperature decrease Starting materials: acryl-amide (AA), N, N'-methylene-bisacrylamide (MBA), Ammonium-persulphate (APS), N, N, N', N'-tetramethylene-diamine (TEMED) In a 100 cm3 20 v% acetone-water mixture we dissolve 15 g AA and 0,133 g MBA. To this we add 80 mg APS and mix 200 Ill TEMED solution. The solution is poured in a 0.5-1 mm gap between the pre-prepared two well sealing, flat glass sheets. After the gelation has completely taken place (approx. 5-8 hours) the intelligent glass may be used.