Optical appearance properties

The optical appearance properties of a polymer, e.g. its clarity, gloss, dullness or turbidity, have no (direct) correlation with its chemical structure they are largely determined by physical factors. Commercially these properties are important. Two groups of appearance properties may be distinguished those connected with the volume (bulk) and those connected with the surface of the material. 

The main volume properties of polymers are colour and transparency. Both may either be inherent to the polymer or caused by additions, e.g. dyes and other additives. Most polymers do not show differential absorption in visible light and are therefore colourless. The volume properties cover a wide range from glass clarity to full opaqueness. This is also the case for the surface properties they may vary from high gloss to full dullness (matt). 

If the transmittance is 90%, the material is called transparent, for lower values it is called translucent. Translucent bodies show loss of contrast and loss of detail. Haze or milkiness is defined as that fraction of the transmitted light that deviates from the transmitted beam by more than It may be caused by flow defects during processing 

The objective measure in this case is the intensity and kind of reflectance. Only for highly polished metal mirrors the reflectance may be nearly total if the specular reflectance is almost nil, the surface is totally matt. In between, the material is glossy or sheeny. Gloss is the reflectance of a surface responsible for its lustrous appearance, commonly at maximum near the specular direction, i.e. the direction of pure mirror reflection. 

The fraction of the light that neither enters the material, nor follows the direction of mirror reflection, is dispersed by diffraction. The lustre of a material is therefore the integral effect of reflection and diffraction. 

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For clusters of higher nuclearity too, the kinetic method for determining the redox potential (M /Mn) is based on electron transfer, for example, from mild reductants of known potential which are used as reference systems, towards charged clusters MjJ. [31] Note that the redox potential differs from the microelectrode potential °(M, M /M ) by the adsorption energy of Mon M (except for = 1). The principle [31 ] is to observe at which step n of the cascade of coalescence reactions, a reaction of electron transfer occurring between a donor S and the cluster could compete with the coalescence. Indeed, n is known from the coalescence rate constant value, measured in the absence of S, and from the time elapsed from the atom appearance to the start of coalescence. The donor S is produced by the same pulse as the atoms M°, the radiolytic radicals being shared between M and S. One form at least in the couple S/S should possess intense optical absorption properties to permit a detailed kinetics study. 

Because its contrast results from a unilateral displacement of beams, DIG provides directional contrast within the image the specimen appears as if illuminated from one side, and is perceived as if three-dimensional , an appearance that may genuinely represent the third dimension, or which may be an artifactual expression of differences of RI. DIG provides a high-resolution image that lacks the haloes of phase contrast, and has excellent optical-sectioning properties for imaging selected planes of focus. 

Laser irradiation of polymeric fibres can be used to generate a morphological modification at the surface of the irradiated regions. The normally smooth surface of synthetic fibres can be modified by this technique to form a regular, ripple-like, structure, which has a significant effect on the physical properties of the fibre, e.g. adhesion of particles and coatings, wetting properties and optical appearance (Knittel and SchoUmeyer, 1998). 

For instance, sensory properties such as texture and optical appearance are of utmost importance for the quality of food products. In living systems, structures and shapes are strongly related to biological functioning. Examples are the influence of the (local) curvature on the barrier properties of biological membranes, the change of shape of blood platelets in the blood clotting process, the influence of shape (aspect ratio) on the toxicity of nanoparticles, and the dependence of enzymatic activity on the three-dimensional structure of protein molecules. 

Another general property of two-phased materials is their optical appearance. Because the phase domains usually have different refractive indices, they scatter light, which results in a hazy, translucent, or milk-white appearance. Such a clouded appearance, along with two glass transition temperatures, has along been accepted as primary evidence of phase separation. Typical data are presented in Table for a fluorocarbon... 

On the other hand, a CW laser produces larger, structural molecules rather than small fragments and stable molecules as opposed to radicals. It appears that heating with a CW laser is a promising method for obtaining molecular information from small sample volumes, but this depends also strongly on the thermal and optical absorption properties of the sample. 

Basically, Newtonian mechanics worked well for problems involving terrestrial and even celestial bodies, providing rational and quantifiable relationships between mass, velocity, acceleration, and force. However, in the realm of optics and electricity, numerous observations seemed to defy Newtonian laws. Phenomena such as diffraction and interference could only be explained if light had both particle and wave properties. Indeed, particles such as electrons and x-rays appeared to have both discrete energy states and momentum, properties similar to those of light. None of the classical, or Newtonian, laws could account for such behavior, and such inadequacies led scientists to search for new concepts in the consideration of the nature of reahty. 

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