Translucent materials liquids

Systematic attempts to formulate improved materials have met with no success (Manly et al., 1951 Rockett, 1968). The last and, in some ways, most promising attempt at improving the dental silicate cement was made by Pendry (Pendry Cook, 1972 Pendry, 1973) who improved its resistance to acid by adding indium to both powder (5-8 %) and liquid (5-65 %). The cement, however, lacked suflScient translucency, and by this time the glass-ionomer cement had arrived with its advantages of translucency and resistance to staining and acid attack. 

The resulting reaction mixture, a clear yellow liquid containing a white opaque solid, is protected from atmospheric moisture by means of a calcium chloride drying tube and is set aside at room temperature for 1.5-2 hours. During this time slight effervescence continues (Note 3) and the white opaque suspended material gradually disintegrates to a finely divided translucent deposit. 

Polyethylene. The most straightforward process for the production of polymers from ethylene is that of the direct polymerization of the olefin. The polymerization process usually requires pressures and temperatures of 15,000 to 30,000 pounds per square inch and 200° to 300° C., and may be effected in either gas or liquid phase reactions (9). The polymer of molecular weight above 20,000 is the white, translucent plastic, polyethylene, widely used in electrical insulation, packaging material for foods, cosmetics and pharmaceuticals, liners for paper bags, etc. Articles molded from polyethylene are semirigid or rigid, depending on their thickness, but in thin films the material has excellent flexibility, even at relatively low temperatures. 

It may polymerise with violence on melting at 86°C [1], The concentrated aqueous solutions of commerce will crystallise in cool weather. The usual industrial technique for softening raw materials, applying a steam hose to the bottom of the container, to which crystals have fallen, will create domains of molten, unstabilised, monomer, initiating polymerisation of the whole, then rupturing containers through steam pressure. Rather, the liquid at the top should be warmed and circulated. Photoinitiation seems involved, black plastic containers give less problem than translucent ones. Best do not store below 15°C [2],... 

Gardener colour A measure of translucency as seen in the case of liquid epoxy resins. The Gardener scale ranges from 1 to 10. Transparent materials have a lower value on the Gardener scale. 

Industrial or synthetic polymers find extensive use in modern day society. They are many in number, polyvinyl chloride (PVC) polyamides (Nylon), polyethylene teraphthalate (PET), polystyrene and polyolefins, to name but a few. Polymers are without exception very complex compounds, capable of manifesting themselves in many shapes and forms. They can exist as viscous liquids, powders, coloured granules, cast or extruded sheet, transparent or translucent film, formulated (in some cases in excess of ten different additives may be added) or unformulated. Hence they can present a very daunting task to the analyst or polymer chemist wishing to fully characterise such materials. 

Because of unfavorable sorption effects on paper that cause tailing, materials with lower adsorptivity were sought. Thus, cellulose acetate [35] and nitrocellulose [36,37] membranes were introduced. Cellulose acetate can be either prepared in the laboratory by treating cellulose with acetic anhydride, or it may be purchased from commercial sources. Cellulose acetate membranes are readily soluble in phenol, glacial acetic acid, dichloromethane and acetone. In part they can be solubilized in several solvent mixtures e.g., chloroform/ethanol (9 1 v/v). For detection (optical scanning) the foil can be made translucent by immersion in cottonseed oil, decalin, liquid paraffin or Whitemore oil 120. 

As already mentioned, liquid crystals are organic materials which are transparent when no electrical field is present and are translucent (scattering) when the field is on because of an orientation of the crystals in the direction of the electrical field, e.g. [157-159]. 

Physical description. The physical description should include the state of the material (solid, liquid), the color, and the consistency (for solids) or viscosity (for liquids). For liquid materials, describe the clarity of the solution (transparent, translucent, or opaque). If an unknown material is a bi- or tri-layered liquid, describe each layer separately, giving an approximate percentage of the total for each layer. Afta- taking appropriate safety precautions for handling the unknown, including the use of personal protection devices, remove a small sample for use in the following tests. 

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