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Welding, G. N. (1961) Osmometry of high polymer solutions. Doctoral thesis, Northern Polytechnic.
To test adequately the theories of polymer solutions in the range of high dilution, osmotic data is needed with a much smiler random error than possible with current methods. The object of the present work was to find an accurate method, and to demonstrate its use.
A comprehensive analysis of osmometer performance has shown a new criterion of speed to be necessary. The analysis has made it possible to predict the performance of an instrument in given circumstances, and to specify the requirements for the desired accuracy.
A number of new forms of cell have been explored, and several techniques of construction were specially developed to enable the requirements to be satisfied. The original features of the final cell included a taut membrane wrapped round a cylinder, an adhesive edge seal, and a cell cavity with closely spaced membrane supports of glass. The cell had an area of membrane increased to 10 times and a liquid thickness behind the membrane reduced to of those of a Fuoss-Mead cell, excellent membrane support and freedom from leaks.
An interferometric detector with a flat liquid surface was specially designed, and separate teats have shown that it would effectively eliminate the errors of current detectors.
The new cell was tested with a double tube detector, enabling the variations in capillary rise during osmotic measurements to be observed for the first ties. Several sources of gross variation were revealed, and eliminated during osmotic measurements. The final determinations of null pressure had a random error of standard deviation 0.00047 gm cm-2, about 20 times the accuracy of current instruments.
For a polystyrene fraction of molecular weight 2.6 x 10 6, virial coefficients have been measured in toluene, showing reliably that the third coefficient, C, does not increase with molecular weight as has sometimes been assumed.
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