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Gel shrinking resulting from uneven distribution of ionic micelles between the inside and the outside of the polymer gel network
Author(s) -
El Sayed A. Mounir,
Kawasaki H.,
Maeda H.
Publication year - 2004
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.20634
Subject(s) - pulmonary surfactant , micelle , self healing hydrogels , polymer , swelling , ionic bonding , chemical engineering , chemistry , osmotic pressure , critical micelle concentration , polymer chemistry , chromatography , materials science , ion , aqueous solution , organic chemistry , biochemistry , engineering
The volume change of crosslinked nonionic poly ( N ‐isopropylacrylamide) (NIPA) polymer gel immersed in tetradecyldimethylaminoxide (C14DMAO) surfactant solutions at 0.1 M NaCl, were investigated to distinguish between binding and nonbinding polymer gel/C14DMAO surfactants. Also, the aggregation behavior of C14DMAO surfactants the inside and the outside the polymer hydrogels has been studied through solubilization of Sudan III dye. For the C14DMAO surfactants at the degrees of ionization (α) of 0.5 and 1, they bind to the NIPA gel at low surfactant concentration (C D ) that enhance the gel swelling due mainly to the osmotic pressure contribution from the counter ions (regime I, C D <10mM). However, the deswelling behavior was observed as the surfactant concentration increases above 10 mM (regime II). The solubilization experiments indicated that the surfactant concentration inside the gel is lower than that outside the gel in the regime II, which may be due to the large micelle size that cannot accommodate the mesh size of the gel. It was suggested that the uneven distribution of the ionic micelles leads to the reduction of the net swelling osmotic pressure of the gel (i.e., the decrease of the gel volume). In the case of the nonionic C14DMAO at α = 0, on the other hand, the deswelling behavior was not clearly observed and the surfactant concentration inside the gel and outside the gel was almost identical even at 30 mM. For the nonionic surfactant, it was also found that the gel volume increases with the surfactant concentration at low surfactant concentration less than 1mM. This may be attribute to the dipole‐dipole repulsion of N ‐O headgroups. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2001–2006, 2004