Stomatosomes, blastula vesicles and bilayer disks: morphological richness of structures formed in dilute aqueous mixtures of a cationic and an anionic surfactant
2009 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 331, no 2, 484-493 p.Article in journal (Refereed) Published
Cryogenic transmission electron microscopy (cryoTEM) was used to study the structures formed in mixts. of sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in dil. aq. solns. with 0-300 mM NaBr. The DTAB mole fraction, X, was in the range 0.2-0.4, limited at 25 DegC by pptn. of solid DTA-DS at X = 0.38 without salt to X = 0.25 at 300 mM NaBr. At a total surfactant concn. of 100 mM the samples sepd. into two liq. phases (the bottom phase birefringent) within a narrow (+-0.01 mol fraction units) compn. range. At the mid-point X varied from 0.32 without salt to 0.22 at 300 mM NaBr. Elemental anal. of C, S, O, and N in the sepd. phases of a sample with 100 mM NaBr and X = 0.26 showed the top phase to contain almost only SDS at a low concn., 14 mM, and the bottom phase 175 mM total surfactant, with X = 0.27 . Elemental anal. on samples without added salt gave erratic results, indicating problems in the phys. sepn. of the phases. The cryoTEM survey of the sepd. phases revealed similar problems. Without salt both phases showed similar structures, whereas the top phase in the sample with added salt was void of structures larger than small micelles. The cryoTEM survey revealed a variety of structures being simultaneously present in most samples. A general trend with increasing X was an evolution from globular micelles, over disks, bands, branched bands transforming into sparse webs, perforated bilayer structures, and finally smooth bilayers. Increasing salt and total surfactant concns. resulted in the emergence of structures with smaller mean curvature at lower X. Perforated bilayers were found in samples with 100 mM or less of added salt, and usually persisted to DTAB contents where ppts. appeared. The porous bilayers seemed to derive from sparse webs of band-like structures, and the hole size decreased with increasing X and salt concn. Two types of recurrent structures were noticed: blastula aggregates, seemingly an intermediate structure transforming crumpled bilayers into vesicles of similar size (diam. 400-500 ANG.), obsd. over a broad range of conditions, and at 100 mM total surfactant concn. and 50 mM added salt or more a type of regular disks with a diam. of 180 +- 30 ANG.
Place, publisher, year, edition, pages
2009. Vol. 331, no 2, 484-493 p.
Catanionic surfactants, Perforated vesicle, Disks, Micelles, CryoTEM, Bilayer
Other Basic Medicine
Research subject Physical Chemistry
IdentifiersURN: urn:nbn:se:uu:diva-88522DOI: 10.1016/j.jcis.2008.11.044ISI: 000263335700034OAI: oai:DiVA.org:uu-88522DiVA: diva2:158541