Crystallinity absorption, effects

Areas of particular interest to the vision area were in defining the rules which determined the absorption effectiveness of a chromophore, the elucidation of the "liquid crystalline" state of matter, the electronic characteristics of useful chromophore and the mechanisms of interfacing between chromophores and their associated "signal" receivers. 

The trend in industrial hygiene work is to identify the particular species responsible for an occupational health problem, although assessment of exposures to inorganic materials previously has most often been based on elemental analysis When a solid inorganic compound is to be identified and quantified, X-ray diffraction should be among the approaches considered This paper has outlined the use of X-ray powder diffraction as a tool for the identification and quantitation of crystalline particulates It has been shown that the substrate standard method is the preferred quantitative procedure for several reasons (1) easy adaptability to most analytes (2) fast analysis time (as compared to the internal standard procedure) and (3) accurate determination of matrix absorption effects While there are a number of reasons why a given compound may not be amenable to this technique, it is likely that the list of analytes will be added to in the future ... 

Crystal orientation In general, the infrared radiation incident on a sample is partially polarised so that the relative intensities of absorption bands may alter as a crystalline sample is rotated. In an orientated crystalline sample, a functional group may be fixed within its lattice in such a position that it will not interact with the incident radiation. These crystalline orientation effects can be dramatic, especially for thin crystalline films or single crystals. 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

The greater the degree of crystallinity the less the water absorption and hence the less will be the effect of humidity on the properties of the polymer. The degree of crystallinity also has an effect on electrical and mechanical properties. In particular high crystallinity leads to high abrasion resistance. 

The practical development of plant sterol drugs as cholesterol-lowering agents will depend both on structural features of the sterols themselves and on the form of the administered agent. For example, the unsaturated sterol sitosterol is poorly absorbed in the human intestine, whereas sitostanol, the saturated analog, is almost totally unabsorbable. In addition, there is evidence that plant sterols administered in a soluble, micellar form (see page 261 for a description of micelles) are more effective in blocking cholesterol absorption than plant sterols administered in a solid, crystalline form. 

The effect of hot water sealing is to convert anhydrous y-AljO, into the crystalline monohydrate, AljOj.HjO, which occupies a greater volume and blocks up the pores, thus preventing further absorption of dyes or contaminants. The monohydrate is also less reactive. 

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

The physicochemical characteristics of the active ingredient in relation to the dosage form and the suitability for its intended purpose was discussed in several EPARs, particularly relating to the solubility characteristics and absorption from the gut. The compression characteristics were also mentioned in some EPARs. The possible effects of different polymorphs or evidence that only a single polymorph is used are addressed as appropriate. Different amorphous or crystalline forms are also discussed. Where affecting the dosage form, selection properties such as unpleasant taste or smell are mentioned. 

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