TY - JOUR
T1 - Alkyl chain symmetry effects in mixed cationic-anionic surfactant systems
AU - Regev, Oren
AU - Khan, Ali
N1 - Funding Information:
Valuable discussions with Håkan Wenneström, Marc Leaver, and John Daicic are kindly acknowledged. O.R. acknowledges a grant from the Swedish Institute. Part of the viscosity measurements were made by Mr. Boaz Eldad. The project is financed by the Swedish Research Council for Engineering Science (TFR).
PY - 1996/9/1
Y1 - 1996/9/1
N2 - We study symmetry effects of hydrophobic tails in mixed oppositely charged surfactant systems. Equal hydrophobicity of the participating surfactants is obtained either (1) by equal hydrocarbon surfactants chain length or (2) by unequal surfactants chain length when one chain is perfluorinated. Three systems were studied: symmetric system of type (1) or (2), and an asymmetric system. Some unusual structural changes are observed in a hydrocarbon-fluorocarbon mixed single-chain oppositely charged surfactant system in the dilute region. Both the cationic hydrocarbon surfactant, dodecytrimethylammoniumchloride (DoTAC), and the anionic fluorocarbon surfactant, sodium perfluorononanoate (SPFN), are separately soluble in water, forming micellar solutions at high water concentration followed by the formation of liquid crystal phases at low water content. Upon mixing the two surfactants in an equimolar ratio at low total surfactant concentration (C < 5 wt%), a stable, dense, flow-birefringent phase is formed at the bottom of the test tube, and a clear phase is formed at the top. Cryo-transmission electron microscopy (cryo-TEM) micrographs of the dense phase show dispersed lamellar droplets having a very small d spacing, and fairly monodispersed ~ 100 nm single-walled vesicles in the supernatant. The latter is supported by NMR self-diffusion measurements. This structural behavior is studied at different molar ratios of the two surfactants. A micelle-vesicle transformation is indicated by NMR self-diffusion measurements. The same behavior is found for symmetry of type (1). The asymmetric system DoTAC-sodium nonanoate (SN) shows an isotropic phase in all molar ratios up to 40 wt% of surfactant, where both imaging and rheological measurements indicate the existence of elongated micelles in the equimolar solution. It was found that the micellar size distribution is coupled with the molar ratio only in the SN-rich part.
AB - We study symmetry effects of hydrophobic tails in mixed oppositely charged surfactant systems. Equal hydrophobicity of the participating surfactants is obtained either (1) by equal hydrocarbon surfactants chain length or (2) by unequal surfactants chain length when one chain is perfluorinated. Three systems were studied: symmetric system of type (1) or (2), and an asymmetric system. Some unusual structural changes are observed in a hydrocarbon-fluorocarbon mixed single-chain oppositely charged surfactant system in the dilute region. Both the cationic hydrocarbon surfactant, dodecytrimethylammoniumchloride (DoTAC), and the anionic fluorocarbon surfactant, sodium perfluorononanoate (SPFN), are separately soluble in water, forming micellar solutions at high water concentration followed by the formation of liquid crystal phases at low water content. Upon mixing the two surfactants in an equimolar ratio at low total surfactant concentration (C < 5 wt%), a stable, dense, flow-birefringent phase is formed at the bottom of the test tube, and a clear phase is formed at the top. Cryo-transmission electron microscopy (cryo-TEM) micrographs of the dense phase show dispersed lamellar droplets having a very small d spacing, and fairly monodispersed ~ 100 nm single-walled vesicles in the supernatant. The latter is supported by NMR self-diffusion measurements. This structural behavior is studied at different molar ratios of the two surfactants. A micelle-vesicle transformation is indicated by NMR self-diffusion measurements. The same behavior is found for symmetry of type (1). The asymmetric system DoTAC-sodium nonanoate (SN) shows an isotropic phase in all molar ratios up to 40 wt% of surfactant, where both imaging and rheological measurements indicate the existence of elongated micelles in the equimolar solution. It was found that the micellar size distribution is coupled with the molar ratio only in the SN-rich part.
KW - cryo-transmission electron microscopy
KW - hydrocarbon-fluorocarbon
KW - mixed surfactant
KW - self-diffusion NMR
KW - symmetry
UR - http://www.scopus.com/inward/record.url?scp=0030248968&partnerID=8YFLogxK
U2 - 10.1006/jcis.1996.0440
DO - 10.1006/jcis.1996.0440
M3 - Article
AN - SCOPUS:0030248968
SN - 0021-9797
VL - 182
SP - 95
EP - 109
JO - Journal of Colloid and Interface Science
JF - Journal of Colloid and Interface Science
IS - 1
ER -