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The surface tension of polymer solutions and asymmetric membrane formation
Author(s) -
Tanny G. B.
Publication year - 1974
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1974.070180721
Subject(s) - surface tension , polymer , polymer chemistry , formamide , cellulose acetate , solvent , materials science , phase diagram , casting , membrane , gibbs isotherm , phase (matter) , chemical engineering , chemistry , thermodynamics , cellulose , organic chemistry , composite material , biochemistry , physics , engineering
The surface concentration of polymer molecules in solution has been combined with the three‐component bulk‐phase diagram of Strathmann et al. to describe the complete equilibrium thermodynamic precasting situation. The polymer surface concentration is estimated according to the theory of Prigogine and Marechal as used by Siow and Patterson, and is governed by the relative values of the polymer and solvent surface tension, γ p and γ s respectively. In general, when γ p > γ s , the cast membrane will tend to form with the asymmetric layer on the support side; for γ p < γ s it will tend to form on the gelation bath side. This was found to be the case for several cellulose acetate casting solutions, including the acetone/formamide mixture of Manjikian. The surface tension of cellulose acetate in the latter mixture appeared to be much lower than in single solvents such as DMSO. The effects of surface tension were used to prepare asymmetric gels of poly(phenylene oxide) and nylon 11 by cooling high‐temperature solutions in which γ s > γ p at the gel transition point.