School of Mathematics and Natural Sciences

Preparation of an "Intelligenten Foil"



Xylene, isomer mixture - DANGER

H226, H304, H312+H332, H315, H319, H335, H373
P210, P260, P280, P301+P310, P305+P351+P338, P370+P378

1,3,3-Trimethylindolino-6'-nitrobenzopyrylospirane (epiropyrane)

Not a dangerous substance according to GHS


Not a dangerous substance according to GHS

Hint: A PET foil of the size DIN A5 (148 mm x 210 mm), which can me aquired by halving a foil of the size DIN A4 (296 mm x 210 mm), will be used to create two "intelligent foils" of the size of roughly 15 cm x 10 cm. The number of group experiments should be determined accordingly. A group of two will coat one DIN A5 sheet, and one portion of the prepared solution is enough to coat two DIN A5 sheets.
The preparation of the solution and of the foil should happen in a darkened room.

Preparation of the solution

Two groups dissolve together 50 mg of spiropyrane in a plastic beaker within 15 mL of xylene. The rough amount is displayed on the right.

Stirr until all of the spiropyrane is dissolved. While stirring with a small glass rod add about 4.5 g of polystyrene (e.g. Styropor from packaging) until the consistency of the solution is like honey. While stirring small gas bubbles will occur, because some gas is enclosed in polystyrene from packaging. To get those bubbles out of the viscous solution keep stirring carefully for a while and knock with the beaker onto the table. Let the solution rest in darkness while fixating the PET sheet.

Fixation the PET sheet and application of the polymer solution

One group fixates their transparent PET sheet of the size Din A5 on a piece of cardboard using adhesive tape, making sure that all the edges are covered with the adhesive tape.

About one fourth of the beaker's contents is poured onto the upper edge of the PET sheet of one group, another fourth is poured onto the middle. The other half is used for the PET sheet of the second group and is applied to it in the same way.

The polymer solution is distributed evenly over the whole pet sheet using a long glas stirr rod, that is put horizontally onto the adhesive tape.

If the sheet isn't covered fully after one pull of the glass stirr rod, then it can be applied a second time, pulling the solution in the other direction.

Warning: Xylene will evaporate quickly during this process and the mixture begins to harden. To avoid ungainly stripes, the glass stirr rod shouldn't be pulled too often over the polymer solution, and the sheet should be placed quickly under a fume cupboard to dry out.

Drying of the sheet

The covered sheet, including the underlying cardboard, is placed for about 30 min. in a fume cupboard to dry out and harden.

The coating can be tested after about 30 min. whether it is dry by carefully touching it with a finger. The sheet can be blow-dried in order to help with the drying and hardening of the coating. For blow-drying only cold or slightly warm air should be used. After the coating has dried fully, the adhesive tape can be removed and the edges of the foil are cut evenly with scissors. The foil is then halved with the scissors so that each half is of roughly the size 15 cm x 10 cm.

Laminating, partitioning and testing

Four coated sheets, the products of two groups, are put into one Din A4 laminating bag, while keeping a gap of about 0.5 cm. The laminating bag is then put into the laminator and the foil is caught with a hand on the other side.

Hint: Make sure that the coated sheets have dried fully - otherwise it can damage the laminator while laminating.

The product of the laminator is partitioned into four "Intelligent Foils" by cutting with the scissors through the gap between the coated sheets. The coated sheets are now scratch resistant and protected from influences of air, water, and other substances.

Using an UV flashlight a first test is carried out: If everything worked, putting the UV flashlight onto the sheet and sliding it over its surface will write or draw an information in blue color onto the "Intelligent Foil". This information will fade in the dark in about 30 minutes.

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