Visible light reflectance

Note 2 The name blue phase derives historically from the optical Bragg reflection of blue light but, because of larger lattice constants, BPs can reflect visible light of longer wavelengths. 

Cholesteric LC materials are able to reflect visible light and also respond to temperature changes causing variations in the shade of the reflected colour. The... 

Van den Weeerd J, van Veen MK, Heeren RMA, Boon JJ (2003) Identification of pigments in paint cross sections by reflection visible light imaging microspectroscopy. Anal Chem 75 716-722. 

Useful applications have been found lor the varied effects of these crystal changes. One of the first came from the properly of selectively reflecting visible light because this is lempcraiurv-dependent. the property can be used as a temperature detector, and in gel lurm liquid crystals have been used lor the early detection of those cancers which cause hot spots in the body. Applications of the smectic modifications arise from their ferroelectric properties this phase can function as a fast-switching light-valve device with memory. This kind of application requires some... 

You should see rainbow patterns from refracted and reflected visible light waves. Violet waves have the shortest wavelength and are refracted at the greatest angle, while red waves have the longest wavelength and are bent at the smallest angle. Therefore, rainbows always are red at the top and violet at the bottom. 

In one sense, this is an easy topic. All of the interactions of light with matter can be described with Maxwell s equations (Griffiths, 1981). However, for the materials chemist faced with the problem of designing a glass lens that does not reflect visible light. Maxwell s equations, in their native state, do not appear to offer a straightforward solution. Fortunately, Maxwell s equations have been solved for most of the problems encountered in materials design. Here, one such case is examined. 

Crystals reflect x-rays somewhat as CDs reflect visible light. The visible light bounces off the grooves in a CD in such a way that the light separates into its various colors, giving the CD a rainbow cast. The various layers in a three-dimensional crystal act somewhat like a miniscule groove pattern in a CD. X-rays bounce off microscopic crystal structures and produce a pattern on an x-ray film. From the particulars of the pattern it is possible to discern the size and structure of a single unit of the crystal. The position of the pieces—atoms, ions, or molecules—that make up the crystal can be extracted from this information. Once the volume of the smallest unit of a crystal and the number of atoms that it holds is known, the mass of just one piece—an atom or a molecule—can be determined from the density. 

The pitch of the helix for compound 42 was found to be approximately 0.2-0.3 xm, thus the material selectively reflects visible light over a wide temperature range. Moreover, the pitch is relatively temperature insensitive thus the material can be used in large area non-absorbing polarizers, or in optical notch filters or reflectors. In addition, in the glassy state the helical macrostructure of the chiral nematic phases is retained, thus similar applications are possible. 

The second ingredient is a mechanism for the state to communicate an unambiguous message. The viewer knows the coin s face by the way it reflects visible light. The optical pattern of the heads (H) state differs from that of tails (T). The previous assembly of nine carbon, eleven hydrogen, one nitrogen, and two oxygen atoms differs from structural isomers such as... 

It was shown that the thickness b of one (hypothetical) layer was inessential for the phenomena. Moreover, the existence of a well-defined thickness would require a special explanation. It seems therefore more reasonable to assume continuous rotation of the principal directions. When the substance reflects visible light, p equals about 0-5 fi and the rotation of the principal directions is about 1° for a monomolecular layer. This must be related... 

The angle at which the fiber is invisible is called the extinction angle, and it repeats every 90° of rotation, as shown in Figure 14.12. At the point of maximum contrast (45°), the colors observed in the fiber are called the interference colors and should not be confused with the true color of the fiber. A colorless nylon fiber will show vivid interference colors because of the way polarized light interacts with the pseudocrystalline nature of file fiber, not because of the way the fiber absorbs or reflects visible light. 

Here, p is the pitch of the helical structure. An is the birefringence of the medium and n is the average refractive index, (rio+n ll. The temperature range over which the cholesteric material selectively reflects visible light is known as the color play of the material. The temperature dependence of the... 

Most of the reported cholesteric copolymers spontaneously develop planar textures which reflect visible light. As a general remark, it is important to note, from an applicative point of view, that amorphous polymeric materials, that do not possess a smectic phase at low temperatures, can preserve their cholesteric structure in the glassy state. 

Titanium dioxide is the most commonly used white pigment in paints. It is also used as a sunblock, preventing harmful UV radiation from reaching the skin and reflecting visible light. 

---