ISSN:
0449-2978
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The adiabatic compressibility for two samples (F-1 with DP-3748 and F-2 with DP-2114) of poly(4-vinyl-N-n-butylpyridinium bromide) in aqueous solution has been determined from ultrasonic velocity and density data. The sample (F-1) with the higher degree of polymerization shows comparatively higher velocity and density in solution. However, the evidence for the difference in compressibility is not very decisive. The apparent molal volume ΦV2 and apparent molal compressibility ΦK2 for F-1 are found to be slightly higher than for F-2. In aqueous solution, the decrement of adiabatic compressibility per unit concentration, (β1 - β)/c, is found to be almost constant throughout the entire concentration range, whereas in the presence of excess added electrolyte (1.0M KBr solution), the compressibility decrement shows a decrease with dilution. The latter values are lower than those found in water, since the molecules, in the presence of excess electrolyte, are coiled up more and are less compressible. The ΦV2 and ΦK2 values in water are constant throughout the entire concentration range, as the free counterions formed on dissociation in the dilute region are not solvated and hence contribute little to the compressibility. On the other hand, in the presence of excess KBr (1.0M), the ΦV2 and ΦK2 values show a sharp decrease with increase of polyelectrolyte concentration and finally attain a constant value. This is explained by the fact that because of the formation of a charge-transfer complex between the bromide ion and the polycation, more than the equivalent number of bromide ions is bound, leaving free an equal amount of K+ ions which are solvated and cause the lowering of apparent volumes and compressibilities. Condensation of charges begins at a certain polyelectrolyte concentration, and no further increase of K+ ions is observed. A special situation arises in 0.1M KBr solution. The ΦV2 and ΦK2 values at first increase sharply with increase of polyelectrolyte concentration, but then level off to attain a constant value, at comparatively high concentration. In 2.0% poly(4-vinyl-N-n-butylpyridinium bromide) solution, the concentration of polymer repeat unit (0.08M) is almost equal to the concentration of the added electrolyte (0.1M KBr) used to suppress dissociation. As the polyelectrolyte concentration in 0.1M KBr solution is progressively decreased, more bromide ions are made available for forming the charge-transfer complex with the polycation, leaving the K+ ions free to contribute to the compressibility.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1969.160070901
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