Naslov
Vesicles from symmetric double tailed alkylbenzenesulphonates

Autori
Jalšenjak, Nenad ; Težak, Đurđica

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
1st Congress of the Croatian Society for Electron microscopy, Zagreb, Croatia, Proceedings / Vranešić, Đuro - Zagreb : Udruga Hrvatskih dragovoljaca Domovinskog Rata, 1999, 78-79

Skup
1st Congress of the Croatian Society for Electron microscopy, May 13-16, 1999, Zagreb, Croatia, Proceedings, 78-79.

Mjesto i datum
Zagreb, Hrvatska, 13.05.1999. - 16.05.1999

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Alkylbenzenesulphonate; Vesicles

Sažetak
The structures of mesophases and isotropic phases containing a lamellar dispersion of vesicles in the binary symmetric double-tailed alkylbenzenesulfonate/water systems were determined using polarized light micro-scopy, Nomarski' differential interference contrast optics light microscopy (DIC LM), and cryo-transmission electron microscopy (Cryo-TEM). In this work the formation of lamellar bilayers or multilayers was presented, exhibiting flat lamellae, lamellae bent into tubules, or vesicles and embedded vesicles of various shapes, sizes and levels of encapsulation. Vesicles were found near the borderline of the two-phase regions. It must be emphasized that the transition between the flat and bent lamellae, governed by the concentration and temperature conditions in the binary systems, can result by the vesicle formation. In the phase diagram the isotropic region (I) is followed by the regions characterized as the isotropic solutions containing vesicles ; these low-viscous and high-viscous phases are denoted as Iv.l and Iv.h, respectively. In the system with C15-benzenesulfonate at the borderline between a low-viscosity solution with vesicles, Iv.l , and the biphasic isotropic + lamellar region, I +La , a region characterized by a high-viscosity solution containing vesicles and the lamellar phase, Iv.h + La was found; the mesomorphic phase exhibits the texture of the lamellar phase; in the isotropic phase optical isotropy either of one or of two liquids has been checked within; one of these isotropic phases can be considered pseudo-isotropic in terms of micro supersaturated domains within the isotropic solution. The Iv.h + La phase can be considered to contain the flat lamellar, La , and in addition, the bent lamellar, vesicle, phases. Both phases can be considered lamellar, containing different structures of the surfactant bilayers. It can be pointed out that the lamellar phase coexisting with the isotropic phase, could change its structure from vesicles to a classical lamellar phase with flat bilayers. The vesicle sizes determined from Cryo-TEM micrographs was 100-370 nm, while the sizes of the encapsulated vesicles were smaller. However, larger structure may have been excluded from the specimen during preparation. In addition, long tubular vesicles were observed in the sample. The 7% and 2% C15-benzenesulfonate/water system was examined using DIC LM and Cryo-TEM, respectively. Originally the sample was prepared with 7% surfactant in water, and for microscopy observations it was diluted to 2%, because the 7% sample was too dense, and thus not suitable for Cryo-TEM[1-3]. To verify that the structure of the 7% sample was not altered by dilution, we examined by light microscopy both the 7% and the 2% C15 in water at room temperature. In both cases similar vesicles were observed, but at 7% the field of view contained too many overlapping structures to yield clear microstructural information. When the sample was diluted to 2%, light microscopy showed the same type of structures, namely, large multilamellar liposomes. Cryo-TEM micrographs show a variety of vesicles of a wide range of shapes, sizes, and levels of encapsulation, indicating that indeed the structure of this phase is that of liposomes and vesicles. The bilayer structures of symmetric double-tailed surfactants with a relatively small head group formed in dilute aqueous solutions were described recently, showing also the globular vesicles [4]. The bilayer structures form lamellar droplets at room temperature, while they show the tubular shape if their formation follows cooling from an isotropic solution. The tubular shape of the lamellar phase can be considered the first stage of the liquid crystalline nucleation given the spontaneous transition from the saturated isotropic solution to the bilayer structures. REFERENCES 1. Bellare, J.R., Davis, H.T., Scriven, L.E., and Talmon, Y., J. Electron Microsc. Tech.. 10, 87 (1988). 2. Talmon, Y., Ber. Bunsen-Ges. Phys. Chemie 100, 364 (1996). 3. Danino, D., Talmon, Y., Lévy, H., Beinert, G., and Zana, R., Science 269, 1420 (1995). 4. Danino, D., Talmon, Y., and Zana, R., J. Colloid Interface Sci. 185, 84 (1997).

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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