ISSN:
1435-1536
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract This paper analyzes the effect of gravity on polymer solutions near the consolute point. Calculations are carried out for monodisperse polystyrene in cyclohexane using the Flory-Huggins expression with a concentration-dependent interaction parameter for the free energy of mixing. Depending on molecular weight and distance to the demixing temperature, the influence of gravity leads to non-negligible gradients of the volume fraction in the one-phase region as well as in the two-phase region. In particular, the effect of gravity on the measurement of the coexistence curve in a finite sample is calculated explicitly. In contrast to theory, experiments show that the concentration remains constant throughout the sample over a period of days as long as the system is kept in the homogenous region. Pronounced concentration gradients, however, are established in the twophase region within approximately one day. These findings are discussed with respect to sedimentation kinetics in terms of the droplet model of critical fluids.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01414954
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