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Stomatosomes, blastula vesicles and bilayer disks: Morphological richness of structures formed in dilute aqueous mixtures of a cationic and an anionic surfactant

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Abstract.
Cryogenic transmission electron microscopy (cryoTEM) was used to study the structures formed in
mixtures of sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in dilute
aqueous solutions with 0–300 mM NaBr. The DTAB mole fraction, X, was in the range 0.2–0.4, limited
at 25 ◦C by precipitation of solid DTA–DS at X = 0.38 without salt to X = 0.25 at 300 mM NaBr. At
a total surfactant concentration of 100 mM the samples separated into two liquid phases (the bottom
phase birefringent) within a narrow (±0.01 mole fraction units) composition range. At the mid-point
X varied from 0.32 without salt to 0.22 at 300 mM NaBr. Elemental analysis of C, S, O, and N in the
separated phases of a sample with 100 mM NaBr and X = 0.26 showed the top phase to contain almost
only SDS at a low concentration, 14 mM, and the bottom phase 175 mM total surfactant, with X = 0.27.
Elemental analysis on samples without added salt gave erratic results, indicating problems in the physical
separation of the phases. The cryoTEM survey of the separated 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 concentrations 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 precipitates
appeared. The porous bilayers seemed to derive from sparse webs of band-like structures, and the hole
size decreased with increasing X and salt concentration. Two types of recurrent structures were noticed:
blastula aggregates, seemingly an intermediate structure transforming crumpled bilayers into vesicles of
similar size (diameter 400–500 Å), observed over a broad range of conditions, and at 100 mM total
surfactant concentration and 50 mM added salt or more a type of regular disks with a diameter of
180±30 Å.

Keywords:
Catanionic surfactants
Perforated vesicle
Disks
Micelles
CryoTEM
Bilayer

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Informasi Detail

Judul Seri

Journal of Colloid and Interface Science

No. Panggil

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Penerbit

London : Elsevier Inc.., 2009

Deskripsi Fisik

Journal of Colloid and Interface Science 331 (2009) 484–493

Bahasa

English

ISBN/ISSN

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Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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