Determination of Density

The densities of polymers can be determined by the pyknometer technique or by the flotation method. In the pyknometer technique the liquid volume displaced by the polymer sample is determined by weighing. Most polymers have a density larger than that of water, which can, therefore, be used as the liquid. Polymers in the form of powders or pressed discs tend to adsorb or occlude air bubbles, which can lead to serious errors. This can be largely prevented by careful degassing of the pyknometer and polymer sample under vacuum before filling with liquid, and/or by addition of a small amount (0.1%) of commercial detergent to lower the surface tension of the water. 

The flotation method is especially suitable for powdered polymers. A liquid of higher density is added to a liquid of lower density until the test particles neither sink nor rise to the surface. The densities of the solid and liquid mixture are then equal and it remains only to determine the density of the latter. The experiment is conducted as follows The powdered polymer is placed in a small beaker with a certain amount of less dense liquid. The heavier liquid is then run in from a burette with gentle stirring until the state of suspension is attained. 

The density of the liquid mixture can be determined using a pyknometer or it can be derived from a previously determined calibration curve. For the determination of densities less than unity (e.g., polyethylene), ethanol/water mixtures are suitable for densities larger than unity one may use mixtures of water with aqueous salt solutions (40% CaCl2 solution = 1.40 g/ml 72% ZnCl2 solution = 1.95 g/ml). The density gradient method, which is an elegant var- 

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MPIF Standard 42, Determination of Density Compacted or SinteredMetal Powder Projects, Metal Powder Industries Federation, Princeton, N.J., 1991. 

The molecular weight (mean relative molecular mass) was obtained by determination of density but, in order to determine that the gas was monatomic and its atomic and molecular weights identical, it was necessary to measure the velocity of sound in the gas and to derive from this the ratio of its specific heats kinetic theory predicts that Cp/C = 1.67 for a monatomic and 1.40 for a diatomic gas. 

The experimental determination of density can be carried out by picnometry, density gradient column or by dilatometry. 

Fields of Application. In SAXS a calibration to absolute intensity is required if extrapolated or integrated numerical values must be compared on an absolute scale. Examples are the determination of density fluctuations or the density difference between matrix and domains as a function of materials composition. 

ISO 3514 1976 Chlorinated polyvinyl chloride (CPVC) pipes and fittings - Specification and determination of density... 

ISO 10119 2002 Carbon fibre - Determination of density ISO 10548 2002 Carbon fibre - Determination of size content... 

H. Nakatsuji, Equation for direct determination of density matrix. Phys. Rev. A 14, 41 (1976). 

Laboratory results may be reported on an as received by volume basis or dry matter by mass basis, depending on whether the sample is considered to be a solid or a liquid. Samples >10% DM are generally treated as solids, and <10% DM as liquids. However, there are frequently exceptions to this rule, e.g. some fibrous samples <10% DM are difficult to pipette, so are analysed on a weight basis, but reported on a volume basis. Some customers can pump thick samples with >10% DM, so need the fertilizer values reported as liquids on a volume basis. Routine determination of density values facilitates calculation and reporting of fertilizer values in either mass or volume units. 

The degree of crystallinity is also reflected in the density of the polymer so that the determination of density provides at least a relative measure for crystallinity. Differential scanning calorimetry (DSC) is frequently applied to determine the crystallinity from the heat of crystallization or melting (see Sect. 2.3.4.8). 

Stettbacher (1945) Determination of Density (pp 7-8) Determination of Heat of Explosion (8-10) Determination of Detonation Velocity by Siemens Spark Chronograph, by Rotating Drum Apparatus and by Dautriche Method (10-13) Determination of Volume of Gases Evolved on Explosion (13-14) Temperature Developed on Explosion (14-16) ... 

The determination of density and viscosity is not necessary when the HTA-3 is manufd at the time of loading... 

Liquid, determination of density and refractive index of, 1029-1034 Liquid ammonia, reactions in, 895-902 Liquids, partially miscible, 17-19 Liquids, supercooled, 22, 23 Liquidus, 26, 33... 

The purity of benzene marketed for most laboratory purposes is usually greater than 95.5% with the principal impurities being toluene and other hydrocarbons with boiling points similar to that of benzene. Methods used to assess the quality of benzene include determination of density, boiling point, distillation characteristics, and specific gravity. Benzene of high purity samples is conveniendy measured by freezing point, as outlined in ASTM ID 1016. 

The application of Archimedes principle to the determination of densities of liquids and solids is illustrated in the next two problems. 

Johnson, "Determination of Density in Chap 6 of A. Weissberger, ed, Physical Methods of Organic Chemistry , 3, Wiley,... 

The protocol described here is based on the relationship between the density of the dispersed phase, the density of the continuous phase, the emulsion density, and the volume fraction, which is a measure of the oil droplet concentration. An essential part of the measurement is the precise determination of density. The method introduced below is the most inexpensive method to accurately determine density, but has the drawback that a relatively large sample volume is required. 

The use of this expression for a variational determination of T is a complex problem because of the /V-representability requirement [15, 16, 17], Nevertheless, there is a renewed interest in this problem and a number of methods, including so called cumulant-based approximations [18, 19] are being put forth as solutions to the representability problem. Although some advances can be obtained for special cases there appears to be no systematic scheme of approximating the density matrix with a well-defined measure of the N-representability error. Obviously, the variational determination of density matrices that are not guaranteed to correspond to an antisymmetric electronic wavefunction can lead to non-physical results. 

It is difficult (if not impossible) to satisfy all of these conditions, as evidenced by the differing experimental data obtained with solvents such as water, methanol, carbon tetrachloride, benzene, and other fluids. Thus, there is always the need to specify the liquid employed for the determination of density by means of this (pycnometer) method. Furthermore, a period of 24 hours may be necessary for the determination because of the need for the liquid to penetrate the pore system of the coal to the maximum extent. 

Anstis, G.R., etal. (1981), Acritical evaluation of indentation techniques for measuring fracture toughness I, Direct crack measurements , J. Am. Ceram. Soc., 64(9), 533-8. AS 1774.5 (1979), The determination of density, porosity and water absorption , Standards... 

BS 903 PA1 Physical testing of rubber part A1 Determination of density... 

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