Spontaneous formation of tubular microstructure vesicle from PTA/SDS system

Abstract

Spontaneous vesicle formation and transformation of vesicle to tubular microstructure have been observed in aqueous mixtures of tri-(n-dodecyl-dimethyl-hydroxypropylammonium chloride) phosphate (PTA) and sodium dedecyl sulfate (SDS), which is supported by negative-staining transmission electron microscopy (TEM), scan electron microscopy (SEM) and dynamic light scattering (DLS).Spherical vesicles aggregate to tubular microstructures with their diameters and lengths respectively of about 100 and 7000 nm in the freshly prepared sample at the molar ratio of PTA/SDS=3/7 and a total surfactant concentration of 0.01 mol/L. The diameter, the length and the quantity of tubular structures all increase with the increase of the total concentration of surfactant and the sample aging.Keywords tri-(n-dodecyl-dimethyl-hydroxypropylammonium chloride) phosphate (PTA), vesicle, tubular microstructure, negativestaining TEM.Vesicles/liposomes are the orderly closed bilayer structures made up of lecithin or synthesis surfactant aggregations and have been studied extensively in the simulation of cell membrane in biology in recent decades. Bangham [1] has prepared multicellular liposome by dispersing lecithin into water under ultrasonication in 1965, which indicated the beginning of vesicle/liposome formation by manual work. As vesicles/liposomes by Bangham's method are not stable enough and the preparation is very complicated, many scientists have focused their studies on the spontaneous formation of vesicles.It is well known that mixed surfactants of cationic and anionic types can increase their surface activity extensively and even exchange some other surface properties under certain conditions [2] . In 1989, Kaler and Zasadzinski [3] prepared spontaneous vesicle at first from the mixture of cationic and anionic surfactants, which immediately inspirited the further investigation in this field. So far, spontaneous vesicles have been formed from cationic and anionic surfactants [3 10] (Lasic [11] and Tondre [12] have given the detailed summary), nonionic surfactants and cosurfactants [13 15] , zwitterionic and anionic surfactants [16] , and anionic surfactants and fatty alcohol [17] .It has been reported that many kinds of aggregations, such as lamellar liquid crystal and micelle, can coexist and change to each other in forms with vesicle. Recently, some special microstructures have also been found in vesicle systems, for example, bilayer tubes with diameters from 15 to 350 nm [18] , 5 to 40 m vesicles and tubular structures [19] . The transition of vesicles to lamellar phase and onion phase with the increasing of surfactant concentration has been observed by Regev [20] . Further studies on the coexistence of vesicle with tubular structure and twist supermolecule also have been reported [21 23] .However, the report on the formation and their properties of tubular structures in an aqueous mixture of surfactants is very little so far. In the present work, we obtained a new system of spherical vesicle and tubular microstructure formed i...