Japanese researchers turn a crab shell transparent

The purpose of the research is to find new materials for making flexible displays for electronic devices or solar cells. After making the crab shell see-through, the team applied the same technique to a material made of crushed chitin and acrylic that was flattened to make a type of transparent paper.

To make the crab transparent, it was first bathed in hydrochloric acid, sodium hydroxide and ethanol to remove everything from the shell that wasn’t chitin, leaving a plain white shell. They then soaked the shell in a bath of an acrylic resin monomer, which caused the chitin to become transparent. The resultant transparent crab retained all of the physical characteristics it had at the onset, which made for a rather odd-looking, eerie, specimen; somewhat reminiscent of a hardened jelly fish.

Another positive aspect of chitin is the fact that it doesn’t expand when heated, a property that would be very useful when making flat or bendable type displays for televisions and computers or in solar cells that could be molded to fit real world surfaces. The paper-like material the team made turned out to be ten times as heat resistant as traditional materials such as glass-fiber epoxies, and it had a high light transmittance to boot.

If chitin turns out to be the next great find in electronic materials science, it will be a lucky thing, as it’s quite plentiful in the natural world and not just in crab shells; it’s found in virtually all crustaceans, as well as many insects and most arachnids. It’s even found in the cell walls of many fungi. Technically defined as a horny polysaccharide, it’s a long chain polymer of a derivative of glucose and its primary use in the human world up to now has been as an ingredient in medicines and industrial products.

More information: Md. Iftekhar Shams, Masaya Nogi, Lars A. Berglund and Hiroyuki Yano, Soft Matter, 2012, Advance Article, DOI: 10.1039/C1SM06785K

Abstract
An optically transparent crab-shell with an intact original shape and substantial morphological detail is presented. Inorganic calcium carbonate particles, proteins, lipids and pigments are removed from a native crab-shell, and the remaining chitin nanofibrous structure is impregnated by a monomer and polymerized. The nanostructural implications for man-made nanocomposites are discussed. An important application of the finding is demonstrated as heterogeneous micro-scale crab shell chitin particles are successfully used to process transparent nanocomposites. The incorporation of nanostructured chitin macro-particles not only retains transparency of the matrix resin but also drastically reduces the coefficient of thermal expansion of the polymer. Moreover, the optical transmittance of the composite is stable over a large range of temperatures despite significant inhomogeneity at the mm scale and the large temperature changes in the refractive index of the resin in its isolated state. This class of materials is an interesting candidate for transparent substrates in next-generation electronic devices such as flexible displays and solar cells.

Journal reference: Soft Matter

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