Density determination by the Archimedes principle

2 Density determinati n by the Archimedes principle The density determination of a polymer may be performed by a simple experiment based on the Archimedes principle. A polymer sample has been immersed in a liquid with known density. The upward pressure which is generated by immersion of the polymer sample into the liquid is equal to the weight of the displaced volume and this can be measured by a balance. A schematic drawing is given in figure IV - 40. 

The spacing between two adjacent planes may be obtained from the Bragg relationship. 

The method has recently also been used to determine the interchain distance in amorphous polyimides from measurements of the maximum in the amorphous scattering [29,30]. It is clear from figure IV - 42 that amorphous scattering will give rise to a broad band, which implies a d-spacing distribution. However, this approach may be considered critically since it uncertain whether eq. IV - 26 may be used for amorphous scattering to obtain quantitative information about interchain distances. 

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