Exploring Materials Engineering



Polymers

The word polymer literally means "many parts." A polymeric solid material may be considered to be one that contains many chemically bonded parts or units which themselves are bonded together to form a solid. Two industrially important polymeric materials are plastics and elastomers. Plastics are a large and varied group of synthetic materials which are processed by forming or molding into shape. Just as we have many types of metals such as aluminum and copper, we have many types of plastics such as polyethylene and nylon. Plastics can be divided into two classes, thermoplastics and thermosetting plastics, depending on how they are structurally and chemically bonded. Elastomers or rubbers can be elastically deformed a large amount when a force is applied to them and can return to their original shape (or almost) when the force is released.

Taken from Principles of Materials Science and Engineering, William F. Smith, McGraw-Hill , Inc., New York.

We are all pretty aware of the various plastic/polymer products in our life. On the left is a montage of typical plastic extrusion products. Plastic parts are often produced by the injection molding process. To get an idea of how this is done, visit the following video site . Along side, we see recognizable applications of polymers: modern telecommunications equipment and the ski boot. Visit the Bayer-Polymers web pages for current applications of advanced polymers.

The basic building block of a plastic is the polymer molecule, a long chain of covalent-bonded atoms, such as the one shown on the right. Secondary bonds then hold groups of polymer chains together to form the polymeric material. The polymer web pages of the Department of Chemistry of the Imperial College of Science, Technology and Medicine in the UK , provide an excellent view of commercially significant polymer molecules. For further definition of polymer structure, you are encouraged to visit the Macrogalleria web pages of the School of Polymers and High Performance Materials at The University of Southern Mississippi (USM). These are excellent pages. You will need to have the plug-in Chemscape Chime installed on your browser to be able to see the macro-molecular views of polymers. Not to worry.... how to download Chemscape Chime is explained on these web pages. Also, for further enlightenment, visit the 'other links' posted on the USM web pages.

Engineers the world over use heat-shrinkable tubing instead of standard approaches to insulation, such as taping or molding in place. The tubing comes in a wide range of sizes, colors, and materials. When heated, it shrinks to conform to the size and shape of the underlying material, making installation fast and easy. How much shrinkage can occur? Check out this Youtube video. Why do you think this plastic tubing has the ability to shrink? If you think you know the answer, check at the following website .

Do you know that recent technological developments have lead to electrically conductive polymers? Semiconductor behavior is now possible using polymeric systems. For example, semiconducting polymers, sandwiched between two electrodes, can generate light of any color. The figure at the right shows polymer materials and their solutions (top), a glass plate covered with a thin polymer film (bottom) and three operating displays of two different colours (in the middle). This technology will lead to OLED (organic light-emitting diode), flat panel displays. Such a display would be light in weight, less power consuming than other alternatives, and perhaps flexible. For more information about engineered polymers, visit the web pages of Philips Research.

Can you think of applications for a OLED display? Maybe you will be the materials engineer on the team that figures out an economical and reliable means to produce a reasonably priced, three-pixcel patterned display, using polymer technology and manufacturing knowhow.

Polymers are materials comprised of long molecular chains. Most polymers are carbon based and have relatively low melting points. Polymers have a very wide range of properties which allow for their extensive use in society. Uses include: car parts, food storage, electronic packaging, optical components, and adhesives. The image is of Styrofoam packaging peanut. The reference source URL is SWEHSC at University of Arizona. There are many SEM-image sites on the Internet. Take a look at 'snow' at this commercial site, as example.


Synthetic fabrics are man-made copies of natural fabrics. Synthetic fibers do not occur in nature as themselves but are usually derivatives of petroleum products. Examples of common synthetic fabrics are polyester, spandex, rayon, and velcro. The image is of Velcro (hook side). A plant in nature gave the inventor of Velcro the idea for the product. Velcro is in the class of materials called polymers. The reference source URL is the Boston Museum of Science

Hook and Loop fabric fasteners were invented in 1941 by George de Mestral after a day of hunting in the Jura Mountains in France. Carefully inspecting the burs in his wool pants and his dog's coat, he found hundreds of little hooks engaging the loops in the material and fur. De Mestral made a machine to duplicate the hooks and loops in nylon. He called his new product VELCRO1 Fasteners, from the French words VELours and CROchet. Today there are thousands of uses for VELCRO1 Brand Fasteners, all thanks to a man hunting with his dog in the mountains.

For more about George de Mestral and other clothing-related inventors and inventions, visit these"Zoomschool" web pages.






We are all familiar with liquid crystal display (LCD) devices, image left. Do you realize liquid crystals are polymeric materials? A liquid crystal is, as the name suggests, a state of matter intermediate between a 'normal' liquid and a solid. Liquid crystal phases are formed from geometrically anisotropic molecules - usually this means they are cigar shaped, though other shapes are possible. In a liquid crystal phase, the polymer molecules have a certain degree of order. In the simplest case, the Nematic phase, the molecules generally point in the same direction but still move around with respect to one another as would be expected in a liquid. Under the influence of an applied electric field, alignment of the polymer molecules gives rise to light absorption. This is illustrated in the principle of operation of a LCD schematic below, taken from the web pages of the Materilas Engineering Group at the University of Manchester. Alternatively, visit the Liquid Crystal Display tutorial of the Holm Glad College, Hong Kong; or visit the Molecular Liquids web pages of the Department of Physics at the University of Bristol.








Now the structure of the liquid crystal molecules is more complex than illustrated in the Principle of Operation schematic, above. The relationship between the actual structure of the molecule and the performance of the LCD is the realm of the polymers scientist or engineer. For detail about liquid crystal technology, please consult the reference source URL: Manchester, UK from which the schematic on the right has been taken.

For interesting 'movies' showing microscopic changes in liquid crystal systems, visit these pages at the Florida State University . If you would like to learn more about polymers and liquid crystals, please visit the Case Western tutorial html pages. This is an excellent introductory source to this most interesting area of materials technology.









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Please send any comments to Patrick P. Pizzo, Professor Emeritus, Materials Engineering Created by Dr. Pizzo on August 1, 1997.
Last Revision, December 07, 2012