Glass-blowing only works because the viscosity of molten glass rises as its temperature falls. If a section becomes too thin, it cools and becomes more viscous; the hotter regions around it stretch preferentially, and soon match it in thickness. The principle also works in the drawing of very fine glass fibres; but fails, sadly, in the drawing of thin glass sheet. Adequate thermal uniformity cannot be maintained over its width.
In this connection Daedalus recalls the wonderful stability and uniformity of a simple soap film. If a region is suddenly thinned, its surface tension rises, and hauls it back to a safe thickness. So Daedalus is seeking a ‘soap’ for molten glass. To have the right surface activity, its molecules must combine a glass-loving grouping with one that is incompatible with glass. A silicate or charged silicone moiety should have the thermal stability for the first role; a good candidate for the second is buckminsterfullerene. Like graphite, it must be utterly incompatible with glass; it has a high (indeed, unknown) melting point; and it can carry side-chains for coupling to the silicon unit. DREADCO's chemists are now at work on the project.
Detergent-laden molten glass will be tricky to handle. Opticians, for whom even tiny bubbles in the melt are a headache, will be horrified by its tendency to froth and foam. (Insulation engineers, however, will welcome glass froth as a product in its own right.) From a free surface of the melt, ultra-thin glass film will simply be pulled between fast-running parallel wires. It will set to a uniform thickness governed by the molecular interaction between its faces, probably a fraction of a micrometre. Thin glass films are amazingly flexible and tenacious, and Daedalus is confident of many new uses for his product. Books with glass pages and fired-in print will endure down the ages, and ultra-thin glass cells will transform chemical spectroscopy. Two-dimensional glass lasers and optical conductors will open new areas of photonics and communications; tough interference filters, beam-splitters, anti-reflection layers and photographic film will invade optics. But the major use will be for glazing. Laminated to both faces of a tough polycarbonate sheet, glass film will give a splendid window material — transparent, hard and smooth as glass itself, unscratchable and unbreakable. Windows, the Achilles' heel of modern houses, shops, offices and vehicles, will be safely armoured at last.
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Jones, D. Ultra-light glazing. Nature 397, 302 (1999). https://doi.org/10.1038/16816
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DOI: https://doi.org/10.1038/16816