Interference color

As a point of interest, it is possible to form very thin films or membranes in water, that is, to have the water-film-water system. Thus a solution of lipid can be stretched on an underwater wire frame and, on thinning, the film goes through a succession of interference colors and may end up as a black film of 60-90 A thickness [109]. The situation is reminiscent of soap films in air (see Section XIV-9) it also represents a potentially important modeling of biological membranes. A theoretical model has been discussed by Good [110]. 

Modulation contrast, like DIG, is a shearing method with the same advantages and disadvantages except that interference colors are absent with modulation contrast. The resolution, in spite of the restricted condenser aperture, is certainly not reduced. If anything, resolution seems to be improved and the images obtained have an excellent quaUty, especially in regard to contrast, one not seen with any other technique except the much more expensive video-enhanced imaging. 

Interferenz-bild, n. interference figure, -er-scheinung, /. interference phenomenon, -farbe, /. interference color, interferieren, v.t. interfere, interimistisch, a. interimistic, temporary, interionisch, a. interionic. 

The same properties hold for colorants in food interference colors, illumination conditions, and fluorescence partially determine the appearance of food. 

Shirozu, H. (1958) X-ray powder patterns and cell dimensions of some chlorites in Japan, with a note on their interference colors. Mineral. J., 2, 209-223. 

Section with glass knives or diamond knife and ultramicrotome. Note Usually thick sections (1 pm) are cut, affixed to glass microscope slides, and stained 5-15 min at 40-50°C with toluidine blue solution (1 g toluidine blue and 1 g of sodium borate in 100 mL H20), The block is then refaced so that the trapezoid encompasses the desired tissue. Thin sections of gray, silver, or gold interference colors are cut. 

Cut the resulting blocks with a diamond knife, and mount sections on nickel grids. It is often advisable to cut the sections slightly thicker than normal such that the interference color of the sections is light gold (see Note 14). 

Opt. Colorless in transmitted light. Often exhibits optical anomalies due to mechanical deformation or aggregation of crystals at times biaxial with small 2F due to the anomalies. Abnormal interference colors, due to marked change of birefringence with wavelength, are often observed. 

Cu-S shares with PbS and Sb-S the distinction of being the first published CD compound [1]. This and (for many decades) snbsequent reports involving CD Cu-S described decomposition of thiosnlphate solntions of Cu salts to give Cu-S films. These (and other, mainly PbS) films were known as lUsterfarben (lustrous colors) due to the varied interference colors obtained on metal substrates by deposition of PbS or Cu-S (see Sec. 2.1 and Sec. 5.2 for more details of the history of these lUsterfarben). As for PbS, very little characterization of these deposits was reported in those early papers apart from their varions colors. 

Reference 92 describes not a normal CD process, but one closer to the SILAR technique described in Sec. 2.11.1. However, while the SILAR method involves dipping the substrate in a solution of one ion (e.g., sulphide), rinsing to remove all but (ideally) a monolayer of adsorbed ions and then dipping in a solution of the other ion (e.g., Ag ), the present technique omits the intermediate rinsing step. This means that a relatively large amount of solution can remain on the substrate between dips, and layer formation proceeds much more rapidly than for SILAR, albeit with less control. A typical rate was 4 nm/dip cycle. In this case, a visible layer of Ag2S formed after several dips. Since interference colors were ob-... 

Finally, one additional observation should be of interest to this group, namely the use of stable interference-colored membranes (ca. 2000 A thick) to enable thicknesses to be studied intermediate between that of the above bilayer (60 A) and Simon s bulk electrodes. This is illustrated in Fig. 3 where the steady-state conductance of stable interference-colored membranes made from GMO/hexadecane (bottom) could be compared with that in black bilayers of GMO/decane (filled circles). At the highest carrier concentration the interference-colored membrane was caused to go black with an applied voltage, giving the 500x increase in conductance indicated by the open circle, which is nicely in agreement with that of the GMO/decane bilayers. 

Even closer to cell membranes than monolayers and bilayers are organized surfactant structures called black lipid membranes (BLMs). Their formation is very much like that of an ordinary soap bubble, except that different phases are involved. In a bubble, a thin film of water — stabilized by surfactants — separates two air masses. In BLMs an organic solution of lipid forms a thin film between two portions of aqueous solution. As the film drains and thins, it first shows interference colors but eventually appears black when it reaches bilayer thickness. The actual thickness of the BLM can be monitored optically as a function of experimental conditions. Since these films are relatively unstable, they are generally small in area and may be formed by simply brushing the lipid solution across a pinhole in a partition separating two portions of aqueous solution. 

A solution of brain lipids was brushed across a small hole in a 5-ml. polyethylene pH cup immersed in an electrolyte solution. As observed under low power magnification, the thick lipid film initially formed exhibited intense interference colors. Finally, after thinning, black spots of poor reflectivity suddenly appeared in the film. The black spots grew rapidly and evenutally extended to the limit of the opening (5, 10). The black membranes have a thickness ranging from 60-90 A. under the electron microscope. Optical and electrical capacitance measurements have also demonstrated that the membrane, when in the final black state, corresponds closely to a bimolecular leaflet structure. Hence, these membranous structures are known as bimolecular, black, or bilayer lipid membranes (abbreviated as BLM). The transverse electrical and transport properties of BLM have been studied usually by forming such a structure interposed between two aqueous phases (10, 17). 

Table 51 shows an overview of pigments with luster effects. Effect pigments can be classified as metal platelets, oxide-coated metal platelets, oxide-coated mica platelets, platelet-like mono-crystals and comminuted PVD-films (Physical Vapor Deposition). Aims of new developments are new effects, colors, improvement of hiding power, increase of the interference color, increase of light and weather stability and improved dispersibility characteristics. Of special interest are pigments which are toxicologically safe and which can be produced by ecologically acceptable processes. 

With the given n1 and n2 values, the maximum and minimum intensities of the reflected light - seen as interference colors - can be calculated and agree well with experimental results [5.206]. Refractive indices of materials commonly used in nacreous pigments follow ... 

In practice, platelet crystals are synthesized with a layer thickness d calculated to produce the desired interference colors (iridescence) [5.206], [5.207], Most nacreous pigments now consist of at least three layers of two materials with different refractive indices (Fig. 73). Thin flakes (thickness ca. 500 nm) of a material with a low refractive index (mica) are coated with a highly refractive metal oxide (e.g., Ti02, layer thickness ca. 50-150 nm). This results in particles with four interfaces that constitute a more complicated but still predictable thin film system. The behavior of more... 

The platelet thickness can be adjusted to produce interference colors by modifying reaction conditions. When aligned with its plane orthogonal to the incident light, the platelet crystal behaves as a thin, solid, optical film (see Fig. 72) with two phase-shifted reflections from the upper and lower crystal planes (the phase boundaries). 

Increasing layer thickness of metal oxide causes different interference colors in reflection. Combination with absorption colorants (e.g., Fe203) produces metallic effects. 

A) Interference colors B) Combination pigments Q Metallic colors... 

The development of the mica-based pigments started with pearlescent colors (Fig. 76 A, TiOz - mica). It was followed by brilliant, mass-tone-colored combination pigments (i.e., mica, Ti02, and another metal oxide) with one color (interference color same as mass tone) or two colors (interference and mass tone different) that depend on composition and viewing angle (Fig. 76 B). In the 1980s further development was made by coating mica particles with transparent layers of iron(III) oxide (Fig. 76 C) [5.222]. 

The sequence of interference colors obtained with increasing Ti02 layer thickness agrees with theoretical calculations in the color space [5.206], [5.224], [5.225]. An experimental development of L a b values is given in Figure 78. 

Figure 78. Experimental dependence of interference colors on the TiOz layer thickness on mica expressed in the Hunter L a b scale (a, b only)...

Iron(III) oxide crystallizes independently of the synthesis route in the a-modification (hematite) after calcination. Brilliant, intense colors are obtained with 50-250 nm layers of Fe203. Absorption and interference colors are formed simultaneously and vary with layer thickness of iron oxide. Especially, the red shades are extremely intensive because interference and absorption enhance each other (Fig. 79). It is possible to produce an intense green-red flop with different viewing angles at a layer thickness similar to a green interference [5.228]. 

Ti02/C/Mica TiOCl2 + C + Mica (precipitation) calcination under N2 silver-grey, interference colors (Carbon inclusion pigments, Fig. 81) [5.233]... 

---