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Polarization
Published in Myeongkyu Lee, Optics for Materials Scientists, 2019
Some crystals such as tourmaline and herapathite exhibit dichroism, preferential absorption of light that is polarized in particular directions. While the original meaning of dichroism is the split of a light beam into two beams of different wavelength (i.e., color), polarization-dependent absorption is also referred to as dichroism. Despite the preferential absorption, these dichroic crystals are seldom used as a linear polarizer. Since the dichroic effect is wavelength-dependent, the crystals appear colored. Another practical limitation is the difficulty of growing them into large sizes. The most widely used linear polarizer is Polaroid H-sheet, which was invented by Land in 1938. When a sheet of polyvinyl alcohol (PVA) is heated and stretched in a certain direction, its long, hydrocarbon molecules are aligned in the direction of stretching and form an array of linear molecular chains. If the sheet is then dipped into a solution of iodine, the iodine attaches to the PVA molecules and makes them conducting along the length of the chains. Valence electrons from the iodine dopant are able to move along the polymer chains, but not transverse to them. Just as in a wire-grid polarizer, light polarized perpendicular to the conducting chains is transmitted while light polarized parallel to them is absorbed. The TA of the polarizer is thus perpendicular to the direction in which the sheet is stretched. The Polaroid H-sheet polarizer, much cheaper than other types of linear polarizer, is widely used for sunglasses, photographic filters, and display devices.
Light
Published in David M. Scott, Industrial Process Sensors, 2018
Polarizing filters such as Polaroid film allow light to pass only if its polarization is aligned in a particular direction. Although improvements have been made since its invention, Polaroid was originally produced by loading a viscous solution of nitrocellulose with microscopic crystals of herapathite (iodoquinine sulfate) and extruding it so that the needlelike crystals become aligned with each other (Land, 1951; Land & Friedman, 1933). Herapathite crystals have the property that they preferentially absorb light whose polarization is not aligned with the crystal lattice, so the film transmits only those light rays that are linearly polarized in the preferred direction.
Polarizers
Published in Roshan L. Aggarwal, Kambiz Alavi, Introduction to Optical Components, 2018
Roshan L. Aggarwal, Kambiz Alavi
Polaroid is the trade name for the most commonly used dichroic material, which is a plastic sheet of iodine-impregnated polyvinyl alcohol (PVA). When a PVA sheet is heated and stretched in one direction, the long polymeric molecules align in the direction of the stretch. The iodine atoms provide electrons, which move easily along the aligned chains but not perpendicular to them. Therefore, light with E-field parallel to the aligned chains is heavily absorbed, and the light with E-field perpendicular to the aligned chains is transmitted. Land includes a summary of the development of sheet polarizers (Land 1951).
Utilisation of waste medicine wrappers as an efficient low-cost electrode material for microbial fuel cell
Published in Environmental Technology, 2020
Md. T. Noori, G. D. Bhowmick, B. R. Tiwari, I. Das, M. M. Ghangrekar, C. K. Mukherjee
Recycled scrap metals were used as cost-effective cathode material by Lefebvre et al. and the energy produced by the system averaged to 0.1 kWh/m3 of wastewater treated [19]. Recently, an interesting finding was reported in which an e-waste ‘Liquid Crystal Polaroid Glass Electrode (LCPGE)’ was used as bifunctional electrode (anode and cathode) material for MFC to simultaneously remove/recover hexavalent chromium ions (Cr6+) and energy production [20]. These are the few examples available till date of using recyclable/waste materials as an electrode for MFCs, therefore further exploration to identify potential waste material to be used as electrodes in MFC is required.